LTC3880/LTC3880-1
1
3880fg
For more information www.linear.com/LTC3880
n PMBus/I2C Compliant Serial Interface
n Telemetry Read Back includes VIN, IIN, VOUT, IOUT,
Temperature and Faults
n Programmable Voltage, Current Limit, Digital
Soft-Start/Stop, Sequencing, Margining, OV/UV
and Frequency Synchronization (250kHz to 1MHz)
n ±0.5% Output Voltage Accuracy Over Temperature
n Integrated 16-Bit ADC
n Internal EEPROM with ECC and Fault Logging
n Integrated Powerful N-Channel MOSFET Gate Drivers
Power Conversion
n Wide VIN Range: 4.5V to 24V
n VOUT Range: 0.5V to 5.4V (4V on VOUT0)
n Analog Current Mode Control Loop
n Supports Power-Up Into Pre-Biased Load
n Accurate PolyPhase
®
Current Sharing for Up to 6 Phases
n Available in a 40-Pin (6mm × 6mm) QFN Package
TYPICAL APPLICATION
DESCRIPTION
Dual Output PolyPhase
Step-Down DC/DC Controller with
Digital Power System Management
The LTC
®
3880/LTC3880-1 are dual, PolyPhase DC/DC
synchronous step-down switching regulator controllers
with an I2C-based PMBus compliant serial interface.
The controllers use a constant frequency, current mode
architecture that is supported by LTpowerPlay™ software
development tool with graphical user interface (GUI).
Switching frequency, output voltage, and device address
can be programmed using external configuration resistors.
Parameters can be set via the digital interface or stored in
EEPROM. Voltage, current, internal/external temperature
and fault status can be read back through the bus interface.
The LTC3880 incorporates a 5V linear regulator while the
LTC3880-1 uses an external 5V supply for minimum power
loss. See comparison to LTC3887 below.
VOUT
Start-Up Time
Max
VOUT0/1
Fast ADC Mode
for 1 Parameter
LTC3887/LTC3887-1 35ms 5.5V/5.5V Yes
LTC3880/LTC3880-1 120ms 4V/5.4V No
FEATURES
APPLICATIONS
n High Current Distributed Power Systems
n Telecom, Datacom and Storage Systems
n Intelligent Energy Efficient Power Regulation
VIN
TG0
0.1µF 0.1µF
1µF
10nF
6.04k
PMBus
INTERFACE
TO/FROM
OTHER LTC DEVICES
WRITE PROTECT
2200pF 2200pF
FAULT MANAGEMENT
SOME DETAILS OMITTED
FOR CLARITY
10µF
1.74k
VOUT1
1.8V
20A
4.99k
10nF 530µF
2.15k
0.2µF
0.2µF
0.56µH
1.0µH
TG1
BG0
PGND
BG1
BOOST0 BOOST1
SW0 SW1
INTVCC
LTC3880
TSNS0 TSNS1
ITHO
SHARE_CLK
WP SGND
SDA
SCL
ALERT
RUN0
RUN1
GPIO0
GPIO1
VDD33
VDD25
ITH1
ISENSEO+ISENSE1+
VSENSEO+VSENSE1
VSENSEO–
ISENSEO–ISENSE1–
VOUT0
3.3V
15A
VIN
SYNC
1µF 1µF
3880 TA01a
+
530µF
+
L, LT, LT C , LT M, PolyPhase, Burst Mode, µModule, Linear Technology and the Linear logo
are registered trademarks and No RSENSE and LTpowerPlay are trademarks of Analog Devices,
Inc. All other trademarks are the property of their respective owners. Protected by U.S. Patents
including 5481178, 5705919, 5929620, 6144194, 6177787, 6580258, 5408150, 7420359.
Licensed under U.S. Patent 7000125 and other related patents worldwide.
LOAD CURRENT (A)
0.01
0
EFFICIENCY (%)
POWER LOSS (W)
10
30
40
50
100
70
0.1 1
3880 TA01b
20
80
90
60
0
2
6
1
4
5
3
10 100
VIN = 12V
VOUT = 1.8V
Efficiency and Power Loss
vs Load Current
LTC3880/LTC3880-1
2
3880fg
For more information www.linear.com/LTC3880
TABLE OF CONTENTS
Features ..................................................... 1
Applications ................................................ 1
Typical Application ........................................ 1
Description.................................................. 1
Table of Contents .......................................... 2
Absolute Maximum Ratings .............................. 4
Pin Configuration .......................................... 4
Order Information .......................................... 4
Electrical Characteristics ................................. 5
Typical Performance Characteristics .................. 10
Pin Functions .............................................. 13
Block Diagram ............................................. 15
Operation................................................... 16
Overview ................................................................. 16
Main Control Loop .................................................. 16
EEPROM ................................................................. 17
Power Up and Initialization ..................................... 18
Soft-Start ................................................................ 18
Sequencing ............................................................. 19
Voltage-Based Sequencing ..................................... 19
Shutdown ............................................................... 19
Light Load Current Operation .................................20
Switching Frequency and Phase .............................20
Output Voltage Sensing ..........................................21
Current Sensing ...................................................... 21
Load Sharing ..........................................................22
External/Internal Temperature Sense ......................22
RCONFIG (Resistor Configuration) Pins ..................23
Fault Detection and Handling ..................................23
Internal Memory with CRC and ECC ................... 24
Serial Interface .......................................................25
Communication Failure ......................................25
Device Addressing ..................................................25
Responses to VOUT and IOUT Faults ........................26
Output Overvoltage Fault Response ...................26
Output Undervoltage Response .........................26
Peak Output Overcurrent Fault Response ........... 26
Responses to Timing Faults ....................................27
Responses to VIN OV Faults ....................................27
Responses to OT/UT Faults .....................................27
Overtemperature Fault Response—Internal ......27
Overtemperature and Undertemperature
Fault Response—Externals ............................... 27
Responses to External Faults .................................27
Bus Timeout Failure ................................................28
Similarity Between PMBus, SMBus and I2C
2-Wire Interface ......................................................28
PMBus Serial Digital Interface ................................ 28
PMBus
Command Summary ............................ 32
PMBus
Commands .................................................32
*Data Format .......................................................... 37
Applications Information ................................ 38
Current Limit Programming ....................................38
ISENSE+ and ISENSE– Pins .........................................38
Low Value Resistor Current Sensing .......................39
Inductor DCR Current Sensing ................................40
Slope Compensation and Inductor Peak Current .... 41
Inductor Value Calculation ...................................... 41
Inductor Core Selection ..........................................42
Power MOSFET and Schottky Diode (Optional)
Selection .................................................................42
Variable Delay Time, Soft-Start and Output Voltage
Ramping .................................................................43
Digital Servo Mode .................................................44
Soft Off (Sequenced Off) ........................................ 44
INTVCC Regulator ....................................................45
Topside MOSFET Driver Supply (CB, DB) ................46
Undervoltage Lockout .............................................46
CIN and COUT Selection ...........................................46
Fault Conditions ...................................................... 47
Open-Drain Pins .....................................................48
Phase-Locked Loop and Frequency
Synchronization ...................................................... 48
Minimum On-Time Considerations..........................49
LTC3880/LTC3880-1
3
3880fg
For more information www.linear.com/LTC3880
TABLE OF CONTENTS
RCONFIG (External Resistor
Configuration Pins) ................................................. 49
Voltage Selection ................................................49
Frequency and Phase Selection Using
RCONFIG ............................................................50
Address Selection Using RCONFIG ..................... 51
Efficiency Considerations .......................................52
Checking Transient Response ................................. 53
PC Board Layout Checklist .....................................54
PC Board Layout Debugging ...................................56
Design Example ...................................................... 57
Connecting the USB to the I2C/SMBus/PMBus
Controller to the LTC3880 In System ......................59
LTpowerPlay: An Interactive GUI for
Digital Power ..........................................................60
PMBus Communication and Command
Processing ..............................................................61
PMBus
Command Details ............................... 63
Addressing and Write Protect ................................. 63
General Configuration Registers ............................. 65
On/Off/Margin ........................................................66
PWM Config ...........................................................68
Voltage ....................................................................70
Input Voltage and Limits .....................................70
Output Voltage and Limits .................................. 71
Current .................................................................... 74
Input Current Calibration ................................... 74
Output Current Calibration ................................. 74
Input Current ...................................................... 74
Output Current ....................................................75
Temperature ............................................................76
External Temperature Calibration........................76
External Temperature Limits ...............................77
Timing ....................................................................78
Timing—On Sequence/Ramp .............................78
Timing—Off Sequence/Ramp ............................79
Precondition for Restart .....................................79
Fault Response .......................................................80
Fault Responses All Faults ..................................80
Fault Responses Input Voltage ...........................80
Fault Responses Output Voltage ......................... 81
Fault Responses Output Current .........................84
Fault Responses IC Temperature ........................85
Fault Responses External Temperature ...............86
Fault Sharing ...........................................................87
Fault Sharing Propagation ..................................87
Fault Sharing Response ...................................... 88
Scratchpad .............................................................89
Identification ...........................................................90
Fault Warning and Status ........................................91
Telemetry ................................................................98
NVM Memory Commands .................................... 101
Store/Restore ................................................... 101
Fault Log Operation .......................................... 102
Fault Logging .................................................... 102
Block Memory Write/Read................................ 107
Typical Applications .................................... 109
Package Description ................................... 114
Revision History ........................................ 115
Typical Application ..................................... 116
Related Parts ............................................ 116
LTC3880/LTC3880-1
4
3880fg
For more information www.linear.com/LTC3880
VIN Voltage ................................................. –0.3V to 28V
Topside Driver Voltages
BOOST1, BOOST0 .................................. –0.3V to 34V
Switch Voltage (SW1, SW0) .......................... –5V to 28V
EXTVCC, INTVCC, (BOOST1 – SW1),
(BOOST0 – SW0) ......................................... –0.3V to 6V
VSENSE0+, VSENSE1, ISENSE0n, ISENSE1n .......... –0.3V to 6V
RUN0, RUN1, SDA, SCL, ALERT ................ –0.3V to 5.5V
ORDER INFORMATION
LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION JUNCTION TEMPERATURE RANGE
LTC3880EUJ#PBF LTC3880EUJ#TRPBF LTC3880UJ 40-Lead (6mm × 6mm) Plastic QFN –40°C to 105°C
LTC3880IUJ#PBF LTC3880IUJ#TRPBF LTC3880UJ 40-Lead (6mm × 6mm) Plastic QFN –40°C to 125°C
LTC3880EUJ-1#PBF LTC3880EUJ-1#TRPBF LTC3880UJ-1 40-Lead (6mm × 6mm) Plastic QFN –40°C to 105°C
LTC3880IUJ-1#PBF LTC3880IUJ-1#TRPBF LTC3880UJ-1 40-Lead (6mm × 6mm) Plastic QFN –40°C to 125°C
Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container.
For more information on lead free part marking, go to: http://www.linear.com/leadfree/
For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/. Some packages are available in 500 unit reels through
designated sales channels with #TRMPBF suffix.
ABSOLUTE MAXIMUM RATINGS
LTC3880 LTC3880-1
3940 38 37 36 35 34 33 32 31
11 20
12 13 14 15
TOP VIEW
41
SGND
UJ PACKAGE
40-LEAD (6mm × 6mm) PLASTIC QFN
16 17 18 19
22
23
24
25
26
27
28
29
9
8
7
6
5
4
3
2
VSENSE0+
VSENSE0–
ISENSE1+
ISENSE1–
ITH0
ISENSE0+
ISENSE0–
SYNC
SCL
SDA
TG1
SW1
TSNS1
VSENSE1
ITH1
VDD33
SHARE_CLK
WP
VDD25
VTRIM1_CFG
TSNS0
SW0
TG0
BOOST0
BG0
VIN
PGND
INTVCC
BG1
BOOST1
ALERT
GPIO0
GPIO1
RUN0
RUN1
ASEL
FREQ_CFG
VOUT0_CFG
VOUT1_CFG
VTRIM0_CFG
21
30
10
1
TJMAX = 125°C, θJA = 33°C/W, θJC = 2.5°C/W
EXPOSED PAD (PIN 41) IS SGND, MUST BE SOLDERED TO PCB
3940 38 37 36 35 34 33 32 31
11 20
12 13 14 15
TOP VIEW
41
SGND
UJ PACKAGE
40-LEAD (6mm × 6mm) PLASTIC QFN
16 17 18 19
22
23
24
25
26
27
28
29
9
8
7
6
5
4
3
2
VSENSE0+
VSENSE0–
ISENSE1+
ISENSE1–
ITH0
ISENSE0+
ISENSE0–
SYNC
SCL
SDA
TG1
SW1
TSNS1
VSENSE1
ITH1
VDD33
SHARE_CLK
WP
VDD25
VTRIM1_CFG
TSNS0
SW0
TG0
BOOST0
BG0
VIN
PGND
EXTVCC
BG1
BOOST1
ALERT
GPIO0
GPIO1
RUN0
RUN1
ASEL
FREQ_CFG
VOUT0_CFG
VOUT1_CFG
VTRIM0_CFG
21
30
10
1
TJMAX = 125°C, θJA = 33°C/W, θJC = 2.5°C/W
EXPOSED PAD (PIN 41) IS SGND, MUST BE SOLDERED TO PCB
PIN CONFIGURATION
(Note 1)
FREQ_CFG, VOUTn_CFG, VTRIMn_CFG,
ASEL, VDD25 ............................................ –0.3V to 2.75V
VDD33, GPIO0, GPIO1, TSNS0, TSNS1, VSENSE0–,
SHARE_CLK, WP, SYNC, ITHn ................. –0.3V to 3.6V
INTVCC Peak Output Current ................................100mA
Operating Junction Temperature Range
(Note 2) ................................................ –40°C to 125°C*
Storage Temperature Range ................ –65°C to 150°C*
*See Derating EEPROM Retention at Temperature in Applications Informa-
tion section for junction temperatures in excess of 125°C.
http://www.linear.com/product/LTC3880#orderinfo
LTC3880/LTC3880-1
5
3880fg
For more information www.linear.com/LTC3880
ELECTRICAL CHARACTERISTICS
The l denotes the specifications which apply over the specified operating
junction temperature range, otherwise specifications are at TA = 25°C. (Note 2) VIN = 12V, VRUN0,1 = 3.3V, fSYNC = 500kHz (externally
driven) unless otherwise specified.
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
Input Voltage
VIN Input Voltage Range (Note 12) l4.5 24 V
IQInput Voltage Supply Current
Normal Operation
(Note 14)
VRUN0,1 = 3.3V, No Caps on TG and BG
VRUN0,1 = 0V
25
20
mA
mA
VUVLO Undervoltage Lockout Threshold
when VIN > 4.3V
VINTVCC/VEXTVCC Falling
VINTVCC/VEXTVCC Rising
3.7
3.95
V
V
tINIT Initialization Time Time from VIN Applied Until the TON_DELAY
Timer Starts
120 ms
Control Loop
VOUT1R0 Full-Scale Voltage Range 0
Set Point Accuracy (0.6V to 5V)
Resolution
LSB Step Size
VOUT_COMMAND(1) = 5.500V (Note 9) l
l
5.4
–0.5
12
1.375
5.6
0.5
V
%
Bits
mV
VOUT1R1 Full-Scale Voltage Range 1
Set Point Accuracy (0.6V to 2.5V)
Resolution
LSB Step Size
VOUT_COMMAND(1) = 2.75V (Note 9) l
l
2.7
–0.5
12
0.6875
2.8
0.5
V
%
Bits
mV
VOUT0R0 Full-Scale Voltage Range 0
Set Point Accuracy (0.6V to 4.096V)
Resolution
LSB Step Size
VOUT_COMMAND(0) = 4.095V (Note 9) l
l
4.0
–0.5
12
1.375
4.2
0.5
V
%
Bits
mV
VOUT0R1 Full-Scale Voltage Range 1
Set Point Accuracy (0.6V to 2.5V)
Resolution
LSB Step Size
VOUT_COMMAND(0) = 2.75V (Note 9) l
l
2.7
–0.5
12
0.6875
2.8
0.5
V
%
Bits
mV
VLINEREG Line Regulation 6V < VIN < 24V l±0.02 %/V
VLOADREG Load Regulation ∆VITH = 1.35V – 0.7V
∆VITH = 1.35V – 2.0V
l
l
0.01
–0.01
0.1
–0.1
%
%
gm0,1 Error Amplifier gmITH0,1 =1.22V 3 mmho
IISENSE0,1 Input Current VISENSE = 5.5V l±1 ±3 µA
VSENSERIN0 VSENSE Input Resistance to Ground 0V ≤ VPIN ≤ 5.5V 41 kΩ
VSENSERIN1 VSENSE Input Resistance to Ground 0V ≤ VPIN ≤ 5.5V 37 kΩ
VIlLIMIT Resolution 3 bits
VILIMMAX Hi Range
Lo Range
l
l
68
44
75
50
82
56
mV
mV
VILMMIN Hi Range
Lo Range
37.5
25
mV
mV
Gate Drivers
TG0,1
tr
tf
TG Transition Time:
Rise Time
Fall Time
(Note 4)
CLOAD = 3300pF
CLOAD = 3300pF
30
30
ns
ns
BG0,1
tr
tf
BG Transition Time:
Rise Time
Fall Time
(Note 4)
CLOAD = 3300pF
CLOAD = 3300pF
30
30
ns
ns
TG/BG t1D Top Gate Off to Bottom Gate On Delay Time (Note 4) CLOAD = 3300pF Each Driver 30 ns
BG/TG t2D Bottom Gate Off to Top Gate On Delay Time (Note 4) CLOAD = 3300pF Each Driver 30 ns
tON(MIN) Minimum On-Time 90 ns
LTC3880/LTC3880-1
6
3880fg
For more information www.linear.com/LTC3880
ELECTRICAL CHARACTERISTICS
The l denotes the specifications which apply over the specified operating
junction temperature range, otherwise specifications are at TA = 25°C. (Note 2) VIN = 12V, VRUN0,1 = 3.3V, fSYNC = 500kHz (externally
driven) unless otherwise specified.
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
OV/UV Output Voltage Supervisor Channel 0
N Resolution 8 Bits
V0RANGE0 Voltage Monitoring Range Range Value = 0 1 4.096 V
V0RANGE1 Voltage Monitoring Range Range Value = 1 0.5 2.7 V
V0OUSTP0 Threshold Programming Step Range Value = 0 22 mV
V0OUSTP1 Threshold Programming Step Range Value = 1 11 mV
V0THACC0 Threshold Accuracy 2V < VOUT0 < 4V Range Value = 0 l±2 %
V0THACC1 Threshold Accuracy 1V < VOUT0 < 2.5V Range Value = 1 l±2 %
tPROPOV0 OV Comparator to GPIO Low Time VOD = 10% of Threshold 35 µs
tPROPUV0 UV Comparator to GPIO Low Time VOD = 10% of Threshold 100 µs
OV/UV Output Voltage Supervisor Channel 1
N Resolution 8 bits
V1RANGE0 Voltage Range Range Value = 0 1 5.5 V
V1RANGE1 Voltage Range Range Value = 1 0.5 2.7 V
V1OUSTP0 Step Size Range Value = 0 22 mV
V1OUSTP1 Step Size Range Value = 1 11 mV
V1THACC0 Threshold Accuracy 2V < VOUT1 < 5V Range Value = 0 l±2 %
V1THACC1 Threshold Accuracy 1V < VOUT1 < 2.5V Range Value = 1 l±2 %
tPROPOV1 OV Comparator to GPIO Low Time VOD = 10% of Threshold 35 µs
tPROPUV1 UV Comparator to GPIO Low Time VOD = 10% of Threshold 100 µs
VIN Voltage Supervisor
N Resolution 8 bits
VINRANGE Full-Scale Voltage 4.5 20 V
VINSTP Step Size 82 mV
VINTHACC Threshold Accuracy 9.0V < VIN < 20V l±2.5 %
VINTHACC\M Threshold Accuracy 4.5V < VIN ≤ 9V l±5 %
tPROPVIN Comparator Response Time
(VIN_ON and VIN_OFF)
VOD = 10% of Threshold 100 µs
Output Voltage Readback
N Resolution
LSB Step Size
16
244
Bits
µV
VOFS Full-Scale Voltage (Note 10) VRUNn = 0V (Note 8) 8 V
VOUT_TUE Total Unadjusted Error (Note 8) VOUTn > 0.6V l0.5 %
VOS Zero-Code Offset Voltage ±500 µV
tCONVERT Conversion Time (Note 6) 90 ms
LTC3880/LTC3880-1
7
3880fg
For more information www.linear.com/LTC3880
ELECTRICAL CHARACTERISTICS
The l denotes the specifications which apply over the specified operating
junction temperature range, otherwise specifications are at TA = 25°C. (Note 2) VIN = 12V, VRUN0,1 = 3.3V, fSYNC = 500kHz (externally
driven) unless otherwise specified.
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
VIN Voltage Readback
N Resolution (Note 5) 10 Bits
VIFS Full-Scale Voltage (Note 11) 38.91 V
VIN_TUE Total Unadjusted Error VVIN > 4.5V (Note 8)
l
0.5
2
%
%
tCONVERT Conversion Time (Note 6) 90 ms
Output Current Readback
N Resolution
LSB Step Size
(Note 5)
0V ≤ |VISENSE+ – VISENSE–| < 16mV
16mV ≤ |VISENSE+ – VISENSE–| < 32mV
32mV ≤ |VISENSE+ – VISENSE–| < 63.9mV
63.9mV ≤ |VISENSE+ – VISENSE–| < 127.9mV
10
15.625
31.25
62.5
125
Bits
µV
µV
µV
µV
IFS Full-Scale Current (Note 7) RISENSE = 1mΩ ±128 A
IOUT_TUE Total Unadjusted Error (Note 8) VISENSE > 6mV (Note 15) l±1 %
VOS Zero-Code Offset Voltage ±28 µV
tCONVERT Conversion Time (Note 6) 90 ms
Input Current and Duty Cycle Readback
D_RES Resolution 10 Bits
D_TUE Total Unadjusted Error 16.3% Duty Cycle –3 3 %
tCONVERT Update Rate (Note 6) 90 ms
Temperature Readback (T0, T1, T2)
TRES_T Resolution 0.25 °C
T0,1_TUE External TSNS TUE ∆VTSNS = 72mV (Note 8) l±3 °C
T2_TUE Internal TSNS TUE VRUN0,1 = 0.0V, fSYNC = 0kHz (Note 8) ±1 °C
tCONVERT_T Update Rate (Note 6) 90 ms
INTVCC Regulator
VINTVCC Internal VCC Voltage No Load (LTC3380) 6V < VIN < 24V 4.8 5 5.2 V
VLDO_INT INTVCC Load Regulation (LTC3380) ICC = 0mA to 50mA 0.5 ±2 %
VDD33 Regulator
VDD33 Internal VDD33 Voltage 4.5V < VINTVCC/VEXTVCC 3.2 3.3 3.40 V
ILIM(VDD33) VDD33 Current Limit VDD33 = GND 70 mA
VDD33_OV VDD33 Overvoltage Threshold 3.5 V
VDD33_UV VDD33 Undervoltage Threshold 3.1 V
VDD25 Regulator
VDD25 Internal VDD25 Voltage 2.25 2.5 2.75 V
ILIM(VDD25) VDD25 Current Limit VDD25 = GND 50 mA
LTC3880/LTC3880-1
8
3880fg
For more information www.linear.com/LTC3880
ELECTRICAL CHARACTERISTICS
The l denotes the specifications which apply over the specified operating
junction temperature range, otherwise specifications are at TA = 25°C. (Note 2) VIN = 12V, VRUN0,1 = 3.3V, fSYNC = 500kHz (externally
driven) unless otherwise specified.
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
Oscillator and Phase-Locked Loop
fOSC Oscillator Frequency Accuracy 250kHz < fSYNC < 1MHz Measured Falling
Edge-to-Falling Edge of SYNC with SWITCH_
FREQUENCY = 250.0.and 1000.0
l±7.5 %
VTH,SYNC SYNC Input Threshold VCLKIN Falling
VCLKIN Rising
1
1.5
V
V
VOL,SYNC SYNC Low Output Voltage ILOAD = 3mA l0.2 0.4 V
ILEAKSYNC SYNC Leakage Current in Slave Mode 0V ≤ VPIN ≤ 3.6V ±5 µA
θSYNC-θ0 SYNC to Ch0 Phase Relationship Based on
the Falling Edge of Sync and Rising Edge of
TG0
MFR_PWM_CONFIG_LTC 3880[2:0] = 0, 2, 3
MFR_PWM_CONFIG_LTC 3880[2:0] = 5
MFR_PWM_CONFIG_LTC 3880[2:0] = 1
MFR_PWM_CONFIG_LTC 3880[2:0] = 4, 6
0
60
90
120
Deg
Deg
Deg
Deg
θSYNC-θ1 SYNC to Ch1 Phase Relationship Based on
the Falling Edge of Sync and Rising Edge of
TG1
MFR_PWM_CONFIG_LTC 3880[2:0] = 3
MFR_PWM_CONFIG_LTC 3880[2:0] = 0
MFR_PWM_CONFIG_LTC 3880[2:0] = 2, 4, 5
MFR_PWM_CONFIG_LTC 3880[2:0] = 1
MFR_PWM_CONFIG_LTC 3880[2:0] = 6
120
180
240
270
300
Deg
Deg
Deg
Deg
Deg
EEPROM Characteristics
Endurance (Note 13) 0°C < TJ < 85°C During EEPROM Write
Operations
l10,000 Cycles
Retention (Note 13) TJ < TJMAX l10 Years
Mass_Write Mass Write Operation Time STORE_USER_ALL, 0°C < TJ < 85°C During
EEPROM Write Operations
l440 4100 ms
Digital Inputs SCL, SDA, RUN0, RUN1, GPIO0, GPIO1
VIH Input High Threshold Voltage SCL, SDA, RUN0, RUN1, GPIO0, GPIO1 l2.0 V
VIL Input Low Threshold Voltage SCL, SDA, RUN0, RUN1, GPIO0, GPIO1 l1.4 V
VHYST Input Hysteresis SCL, SDA 0.08 V
CPIN Input Capacitance 10 pF
Digital Input WP
IPUWP Input Pull-Up Current WP 10 µA
Open-Drain Outputs SCL, SDA, GPIO0, GPIO1, ALERT, RUN0, RUN1, SHARE_CLK
VOL Output Low Voltage ISINK = 3mA l0.4 V
Digital Inputs SHARE_CLK, WP
VIH Input High Threshold Voltage l1.5 1.8 V
VIL Input Low Threshold Voltage l0.6 1 V
Leakage Current SDA, SCL, ALERT, RUN0, RUN1
IOL Input Leakage Current 0V ≤ VPIN ≤ 5.5V l±5 µA
Leakage Current GPIO0, GPIO1
IGL Input Leakage Current 0V ≤ VPIN < 3.6V l ±2 µA
LTC3880/LTC3880-1
9
3880fg
For more information www.linear.com/LTC3880
The l denotes the specifications which apply over the specified operating
junction temperature range, otherwise specifications are at TA = 25°C. (Note 2) VIN = 12V, VRUN0,1 = 3.3V, fSYNC = 500kHz (externally
driven) unless otherwise specified.
ELECTRICAL CHARACTERISTICS
Note 1: Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
Note 2: The LTC3880/LTC3880-1 are tested under pulsed load conditions
such that TJ ≈ TA. The LTC3880E/LTC3880E-1 are guaranteed to meet
performance specifications from 0°C to 85°C. Specifications over the
–40°C to 105°C operating junction temperature range are assured by
design, characterization and correlation with statistical process controls.
The LTC3880I/LTC388I-1 are guaranteed over the full –40°C to 125°C
operating junction temperature range. TJ is calculated from the ambient
temperature TA and power dissipation PD according to the following
formula:
TJ = TA + (PD • θJA)
The maximum ambient temperature consistent with these specifications
is determined by specific operating conditions in conjunction with board
layout, the rated package thermal impedance and other environmental
factors.
Note 3: All currents into device pins are positive; all currents out of device
pins are negative. All voltages are referenced to ground unless otherwise
specified.
Note 4: Rise and fall times are measured using 10% and 90% levels. Delay
times are measured using 50% levels.
Note 5: The data format in PMBus is 5 bits exponent (signed) and 11 bits
mantissa (signed). This limits the output resolution to 10 bits though the
internal ADC is 16 bits and the calculations use 32-bit words.
Note 6: The data conversion is done in round robin fashion. All inputs
signals are continuously converted for a typical latency of 90ms.
Note 7: The IOUT_CAL_GAIN = 1.0mΩ and MFR_IOUT_CAL_GAIN_TC =
0.0. Value as read from READ_IOUT in amperes.
Note 8: Part tested with PWM disabled. Evaluation in application
demonstrates capability. TUE (%) = ADC Gain Error (%) + 100 • [Zero
Code Offset + ADC Linearity Error]/Actual Value.
Note 9: All VOUT commands assume the ADC is used to auto-zero the
output to achieve the stated accuracy. LTC3880 is tested in a feedback
loop that servos VOUT to a specified value.
Note 10: The maximum VOUT voltage is 5.5V.
Note 11: The maximum VIN voltage is 28V.
Note 12: When VIN < 6V, INTVCC must be tied to VIN.
Note 13: EEPROM endurance and retention are guaranteed by design,
characterization and correlation with statistical process controls. The
minimum retention specification applies for devices whose EEPROM
has been cycled less than the minimum endurance specification. The
RESTORE_USER_ALL command (NVM read) is valid over the entire
operating junction temperature range.
Note 14: The LTC3880-1 quiescent current (IQ) equals the IQ of VIN plus
the IQ of EXTVCC.
Note 15: Guaranteed with a common mode voltage (VOUT) between 0V
and5.5V.
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
Digital Filtering of GPIO0, GPIO1
IFLTG Input Digital Filtering GPIO 3 µs
Digital Filtering of RUN0, RUN1
IFLTG Input Digital Filtering RUN 10 µs
PMBus Interface Timing Characteristics
fSMB Serial Bus Operating Frequency l10 400 kHz
tBUF Bus Free Time Between Stop and Start l1.3 µs
tHD,STA Hold time After Repeated Start Condition.
After this Period, the First Clock is Generated
l0.6 µs
tSU,STA Repeated Start Condition Setup Time l0.6 µs
tSU,STO Stop Condition Setup Time l0.6 µs
tHD,DAT Data Hold Time
Receiving Data
Transmitting Data
l
l
0
0.3
0.9
µs
µs
tSU,DAT Data Setup Time
Receiving Data
l
0.1
µs
tTIMEOUT_SMB Stuck PMBus Timer Non-Block Reads
Stuck PMBus Timer Block Reads
Measured from the Last PMBus Start Event 32
150
ms
ms
tLOW Serial Clock Low Period l1.3 10000 µs
tHIGH Serial Clock High Period l0.6 µs
LTC3880/LTC3880-1
10
3880fg
For more information www.linear.com/LTC3880
TYPICAL PERFORMANCE CHARACTERISTICS
Load Step
(Burst Mode Operation)
Load Step
(Forced Continuous Mode)
Load Step
(Pulse-Skipping Mode)
Efficiency vs Load Current,
VOUT = 1.8V (LTC3880)
Efficiency vs Load Current,
VOUT = 3.3V (LTC3880)
Efficiency and Power Loss
vs Input Voltage (LTC3880)
Inductor Current at Light Load Start-Up into a Pre-Biased Load Soft-Start Ramp
LOAD CURRENT (mA)
30
EFFICIENCY (%)
90
100
20
10
80
50
70
60
40
10 1000 10000 100000
3880 G01
0
100
CCM
DCM
BM
VIN = 12V
fSW = 364kHz
L = 0.56µH
DCR = 1.8m
LOAD CURRENT (mA)
30
EFFICIENCY (%)
90
100
20
10
80
50
70
60
40
10 1000 10000 100000
3880 G02
0
100
CCM
DCM
BM
VIN = 12V
fSW = 370kHz
L = 0.56µH
DCR = 1.8m
INPUT VOLTAGE (V)
5
88.0
EFFICIENCY (%)
POWER LOSS (mW)
88.5
89.0
89.5
90.0
90.5
91.0
1800
1900
2000
2100
2200
2300
2400
2500
7 9 11 13
3880 G03
15
VOUT = 1.8V
IOUT = 10A
ILOAD
5A/DIV
INDUCTOR
CURRENT
5A/DIV
VOUT
100mV/DIV
AC-COUPLED
50µs/DIVVIN = 12V
VOUT = 1.8V
0.3A TO 5A STEP
3880 G04
ILOAD
5A/DIV
INDUCTOR
CURRENT
5A/DIV
VOUT
100mV/DIV
AC-COUPLED
50µs/DIVVIN = 12V
VOUT = 1.8V
0.3A TO 5A STEP
3880 G05
ILOAD
5A/DIV
INDUCTOR
CURRENT
5A/DIV
VOUT
100mV/DIV
AC-COUPLED
50µs/DIVVIN = 12V
VOUT = 1.8V
0.3A TO 5A STEP
3880 G06
RUN
2V/DIV
VOUT
1V/DIV
5ms/DIVtRISE = 10ms
tDELAY = 5ms
3880 G08
FORCED
CONTINUOUS
MODE
2A/DIV
Burst Mode
OPERATION
2A/DIV
PULSE-SKIPPING
MODE
2A/DIV
1µs/DIVVIN = 12V
VOUT = 1.8V
ILOAD = 100µA
3880 G07
RUN
2V/DIV
VOUT
1V/DIV
5ms/DIVtRISE = 10ms
tDELAY = 5ms
3880 G09
LTC3880/LTC3880-1
11
3880fg
For more information www.linear.com/LTC3880
TYPICAL PERFORMANCE CHARACTERISTICS
Soft-Off Ramp
Current Sense Threshold
vs ITH Voltage (Low Range)
Maximum Current Sense Threshold
vs Duty Cycle, VOUT = 0V
Maximum Current Sense Threshold
vs Common Mode Voltage
Regulated Output
vs Temperature
SHARE_CLK Frequency
vs Temperature
SHARE-CLK Frequency vs VIN Quiescent Current vs Temperature VOUT Measurement vs VOUT
RUN
2V/DIV
VOUT
1V/DIV
5ms/DIVtFALL = 5ms
tDELAY = 10ms
3880 G10
VITH (V)
0
CURRENT LIMIT (A) WITH 1mΩ SENSE RESISTOR
10
20
30
1.5 2.5
3880 G11
0
–10
–20 0.5 1 2
40
50
60
VSENSE 50mV
VSENSE 25mV
DUTY CYCLE (%)
0
MAXIMUM CURRENT SENSE THRESHOLD (mV)
51
53
55
90
3880 G12
49
47
50
52
54
48
46
45 30 50 70
50mV SENSE CONDITION
COMMON MODE VOLTAGE (V)
0
45
MAXIMUM CURRENT SENSE THRESHOLD (mV)
47
49
51
123 4
3880 G13
5
53
55
46
48
50
52
54
6
50mV SENSE CONDITION
TEMPERATURE (°C)
–50
0.4975
VOUT (V)
0.4980
0.4990
0.4995
0.5000
0.5025
0.5010
–10 30 50
3880 G14
0.4985
0.5015
0.5020
0.5005
–30 10 70 90 110
TEMPERATURE (°C)
–50
90
SHARE_CLK FREQUENCY (kHz)
95
100
105
110
–30 –10 10 30
3880 G15
50 70 90 110
VIN (V)
6
SHARE_CLOCK FREQUENCY (kHz)
100.0
100.5
22
3880 G16
99.5
99.0 10 14 16 2826
101.0
18
812 24
20
TEMPERATURE (°C)
–50
15
QUIESCENT CURRENT (mA)
20
25
30
–30 –10 10 30
3880 G17
50 70 90 110
VOUT (V)
0.5
MEASSURED ERROR (mV)
0.30
0.20
0.10
0
–0.10
–0.20
–0.30
–0.40
4.5
3880 G18
1.5 2.5 3.5 5.541 2 3 5
LTC3880/LTC3880-1
12
3880fg
For more information www.linear.com/LTC3880
TYPICAL PERFORMANCE CHARACTERISTICS
VOUT Command INL VOUT Command DNL INTVCC Line Regulation
VOUT OV Threshold
vs Temperature (1V Target)
VOUT OV Threshold
vs Temperature (2V Target)
VOUT OV Threshold
vs Temperature (4V Target)
VOUT (V)
–1.0
INL (LSBs)
0
1.0
2.0
–0.5
0.5
1.5
1.5 2.5 3.5 4.5
3880 G19
5.510.5 2 3 4 5
VOUT (V)
–0.3
DNL (LSBs)
–0.1
0.1
0.3
–0.2
0
0.2
1.5 2.5 3.5 4.5
3880 G20
5.510.5 2 3 4 5
VIN (V)
5
4.50
4.75
5.25
20
3880 G21
4.25
4.00
10 15 25
3.75
3.50
5.00
INTV
CC
(V)
TEMPERATURE (°C)
–50
0.990
1V OV THRESHOLD (V)
0.995
1.000
1.005
1.010
–30 –10 10 30
3880 G22
50 70 90 110
TEMPERATURE (°C)
–50
1.97
2V OV THRESHOLD (V)
1.98
1.99
2.00
2.01
0 50 100 150
3880 G23
2.02
2.03
–25 25 75 125
TEMPERATURE (°C)
–50
3.96
4V OV THRESHOLD (V)
3.97
3.98
3.99
4.00
0 50 100 150
3880 G24
4.02
4.01
4.03
4.04
–25 25 75 125
Temperature Error
vs Temperature
IOUT Error vs IOUT Room
Temperature IIN Measurement Error vs IIN
ACTUAL TEMPERATURE (°C)
–45
–1.0
MEASUREMENT ERROR (°C)
–0.8
–0.4
–0.2
0
1.0
0.4
–5 35 55
3880 G25
–0.6
0.6
0.8
0.2
–25 15 75 95 115
OUTPUT CURRENT (A)
0
MEASUREMENT ERROR (mA)
0
2
4
20
3880 G26
–2
–4
–8 510 15
–6
8
6
IIN (A)
0
I
IN
MEASUREMENT ERROR (mA)
–4
–2
0
1.2
3880 G27
–6
–8
0.4 0.8
0.2 1.4
0.6 1.0 1.6
–10
–12
2
LTC3880/LTC3880-1
13
3880fg
For more information www.linear.com/LTC3880
PIN FUNCTIONS
VSENSE0+ (Pin 1): Channel 0 Positive Voltage Sense Input.
VSENSE0– (Pin 2): Channel 0 Negative Voltage Sense Input.
ITH0/ITH1 (Pin 5/Pin 26 ): Current Control Threshold and
Error Amplifier Compensation Nodes. Each associated
channel’s current comparator tripping threshold increases
with its ITH voltage.
ISENSE0+/ISENSE1+ (Pins 6/Pin 3): Current Sense Compara-
tor Inputs. The (+) inputs to the current comparators are
normally connected to DCR sensing networks or current
sensing resistors.
ISENSE0–/ISENSE1– (Pin 7/Pin 4): Current Sense Comparator
Inputs. The (–) inputs are connected to the low side of the
current sense element.
SYNC (Pin 8): External Clock Synchronization Input and
Open-Drain Output Pin. If an external clock is present at
this pin, the switching frequency will be synchronized to
the external clock. If clock master mode is enabled, this
pin will pull low at the switching frequency with a 500ns
pulse to ground. A resistor pull up to 3.3V is required in
the application if the LTC3880 is the master.
SCL (Pin 9): Serial Bus Clock Input. Open-drain output,
can hold the output low if clock stretching is enabled. A
pull-up resistor to 3.3V is required in the application.
SDA (Pin 10): Serial Bus Data Input and Output. A pull-up
resistor to 3.3V is required in the application.
ALERT (Pin 11): Open-Drain Digital Output. Connect the
SMBALERT signal to this pin. A pull-up resistor to 3.3V
is required in the application.
GPIO0/GPIO1 (Pin 12/Pin 13): Digital Programmable
General Purpose Inputs and Outputs. Open-drain output.
A pull-up resistor to 3.3V is required in the application.
RUN0/RUN1 (Pin 14/Pin 15): Enable Run Input. Logic
high on these pins enables the controller. Open-drain
output holds the pin low until the LTC3880 is out of reset.
A pull-up resistor to 3.3V is required in the application.
ASEL (Pin 16): Serial Bus Address Configuration Input.
Connect a ±1% resistor divider between the chip VDD25
ASEL and SGND in order to select the 4LSBs of the se-
rial bus interface address. A resistor divider on ASEL is
recommended if there are more than 1 LTC3880 on the
same board to assure the user can independently program
each IC. If the pin is left open, the IC will use the value
programmed in the NVM. Minimize capacitance when the
pin is open to assure accurate detection of the pin state.
TYPICAL PERFORMANCE CHARACTERISTICS
DC Output Current Matching in a
2-Phase System (LTC3880)
TOTAL CURRENT (A)
0
CHANNEL CURRENT (A)
15
20
25
15 25 40
3880 G28
10
5
05 10 20 30 35
CHAN 0
CHAN 1
Dynamic Current Sharing During a
Load Transient in a 4-Phase System
10
0
CURRENT
5A/DIV
5µs/DIV 3880 G29
10
0
CURRENT
5A/DIV
5µs/DIV 3880 G30
Dynamic Current Sharing During a
Load Transient in a 4-Phase System
LTC3880/LTC3880-1
14
3880fg
For more information www.linear.com/LTC3880
PIN FUNCTIONS
FREQ_CFG (Pin 17): Frequency or Phase Set/Select Pin.
Connect a ±1% resistor divider between the chip VDD25
FREQ_CFG and SGND in order to select switching frequency
or phase. If the pin is left open, the IC will use the value
programmed in the NVM. Minimize capacitance when the
pin is open to assure accurate detection of the pin state.
VOUT0_CFG/VOUT1_CFG (Pin 18/Pin 19): Output Voltage
Select Pin. Connect a ±1% resistor divider between the
chip VDD25 VOUTn_CFG and SGND in order to select output
voltage. This voltage can be adjusted with the VTRIMn_CFG
pins. If the pin is left open, the IC will use the value pro-
grammed in the NVM. Minimize capacitance when the
pin is open to assure accurate detection of the pin state.
VTRIM0_CFG/VTRIM1_CFG (Pin 20/Pin 21): Voltage Trim
Select Pin. Connect a ±1% resistor divider between the
chip VDD25 VTRIMn_CFG and SGND in order to adjust
the output voltage set point. The VTRIMn_CFG settings
in conjunction with the VOUTn_CFG setting adjusts the
voltage set point. If the pin is left open, the IC will either
not modify the VOUTn_CFG setting or use NVM. Minimize
capacitance when the pin is open to assure accurate de-
tection of the pin state.
VDD25 (Pin 22): Internally Generated 2.5V power Supply
Output Pin. Bypass this pin to SGND with a low ESR 1µF
capacitor. Do not load this pin with external current except
for the ±1% resistor dividers required for the configura-
tion pins.
WP (Pin 23): Write Protect Pin Active High. An internal
10µA current source pulls the pin to VDD33. If WP is high,
the PMBus writes are restricted.
SHARE_CLK (Pin 24): Share Clock, Bidirectional Open-
Drain Clock Sharing Pin. Nominally 100kHz. Used to
synchronize the timing between multiple LTC3880s. Tie all
SHARE_CLK pins together. All LTC3880s will synchronize
to the fastest clock. A pull-up resistor to 3.3V is required.
VDD33 (Pin 25): Internally Generated 3.3V Power Supply
Output Pin. Bypass this pin to SGND with a low ESR 1µF
capacitor. Do not load this pin with external current except
for the pull-up resistors required for GPIOn, SCLK, SYNC
and possibly RUNn, ALERT, SDA and SCL.
VSENSE1 (Pin 27): Channel 1 Voltage Sense Input. This
input voltage is referenced to the SGND pin.
INTVCC (Pin 33): LTC3880: Internal Regulator 5V Out-
put. The control circuits are powered from this voltage.
Decouple this pin to PGND with a minimum of 4.7µF low
ESR tantalum or ceramic capacitor.
EXTVCC (Pin 33): LTC3880-1: External Regulator 5V in-
put. The control circuits are powered from this voltage.
Decouple this pin to PGND with a minimum of 4.7µF low
ESR tantalum or ceramic capacitor.
PGND (Pin 34): Power Ground Pin. Connect this pin closely
to the sources of the bottom N-channel MOSFETs, the (–)
terminal of CVCC and the (–) terminal of CIN.
VIN (Pin 35): LTC3880: Main Input Supply. Decouple this
pin to PGND with a capacitor (0.1µF to 1µF). For applica-
tions where the main input power is 5V, tie the VIN and
INTVCC pins together. LTC3880-1: Input Voltage Sense.
Should be connected to the external power MOSFET supply.
BG0/BG1 (Pin 36/Pin 32): Bottom Gate Driver Outputs.
These pins drive the gates of the bottom N-Channel
MOSFETs between PGND and INTVCC.
BOOST0/BOOST1 (Pin 37/Pin 31): Boosted Floating Driver
Supplies. The (+) terminal of the booststrap capacitors
connect to these pins. These pins swing from a diode
voltage drop below INTVCC up to VIN + INTVCC.
TG0/TG1 (Pin 38/Pin 30): Top Gate Driver Outputs. These
are the outputs of floating drivers with a voltage swing
equal to INTVCC superimposed on the switch node voltages.
SW0/SW1 (Pin 39/Pin 29): Switch Node Connections to
Inductors. Voltage swings at the pins are from a Schottky
diode (external) voltage drop below ground to VIN.
TSNS0/TSNS1 (Pin 40/Pin 28): Channel 0,1 External
Diode Temperature Sense. Connect to the anode of a diode
connected PNP transistor and star connect the cathode to
SGND in order to sense remote temperature. If external
temperature sense elements are not installed, short pin
to ground and set the UT_FAULT_LIMIT to –275°C,
IOUT_CAL_GAIN_TC set to zero and the UT_FAULT_RE-
SPONSE to ignore.
SGND (Exposed Pad Pin 41): Signal Ground. All small-
signal and compensation components should connect to
this ground, which in turn connects to PGND at one point.
LTC3880/LTC3880-1
15
3880fg
For more information www.linear.com/LTC3880
BLOCK DIAGRAM
16-BIT
ADC
8-BIT VIN
DAC
PWM1
+
–
–
+
–
–
+
+
+
+
–
–
PWM0
–
+
VSENSE1
–
+ISENSE1–
–ISENSE1+
+
8:1
MUX
TMUX
2µA
ILIM DAC
(3 BITS)
OV
8-BIT
OV
DAC
8-BIT
UV
DAC
12-BIT
SET POINT
DAC
UVEA
+
0.56V
1.22V
BURST
ITH0
RC
CC1
30µA
–
+
–
+
AO
R
R
9R
2R
SGND
PWM
CLOCK
VOUT0_CFG
R
VSENSE0+
SGND
TSNS0
VSENSE0–
NO DIFF AMP ON CH1
R
SWITCH
LOGIC
AND
ANTI-
SHOOT-
THROUGH
OV
RUN
SS
UVLO
REV
UV
ON
FCNT
1
2
41
40
18
VOUT1_CFG
19
VTRIM0_CFG
20
VTRIM1_CFG
21
FREQ_CFG
17
ASEL
3880 F01
16
13
12
15
14
PGND
CVCC
34
BG0
DB
M1
VIN
CIN
INTVCC/EXTVCC
VDD33
36
ISENSE0–
7
ISENSE0+
6
SW0
39
TG0 CB
38
BOOST0
37
VDD33
25
INTVCC/EXTVCC (LTC3880-1)
33
M2
COUT
VOUT0
+
3.3V
SUBREG
2.5V
SUBREG
VIN
35
5V REG
38R
R
SGND
–
+
–
+
–
+
1
71.1k
ACTIVE
CLAMP
UVLOINTVCC
SLOPE
COMPENSATION
SLAVE
VDD33
MISO
MOSICLK
MASTER
RAM
RUN0
RUN1
24
SHARE_CLK
GPIO0
GPIO1
EEPROM
MAIN
CONTROL
PROGRAM
ROM
VDD33
COMPARE
ILIM RANGE SELECT
HI: 1:1
LO: 1:1.5
3k
ICMP IREV
5
+
–
+
–
VIN ON/OFF
+
–
S
REF
VSTBY
SGND
Q
PWM_CLOCK
R
PHASE DET
VCO
PHASE SELECTOR
CLOCK DIVIDER
SINC3UVLO OSC
(32MHz)
CONFIG
DETECT
CHANNEL
TIMING
MANAGEMENT
11
10
9
23
WP
SCL
SDA
ALERT
PMBus
INTERFACE
(400kHz
COMPATIBLE)
SYNC
SGND
M3
SGND
VDD33
8
VDD25
22
VDD25
+
LTC3880
ONLY
19R
R
Figure 1. Block Diagram
(One of two channels (CH0) shown)
LTC3880/LTC3880-1
16
3880fg
For more information www.linear.com/LTC3880
OPERATION
OVERVIEW
The LTC3880 is a dual channel/dual phase, constant fre-
quency, analog current mode controller for DC/DC step-
down applications with a digital interface. The LTC3880
digital interface is compatible with PMBus which supports
bus speeds of up to 400kHz. A typical application circuit
is shown on the first page of this data sheet.
Major features include:
n Programmable Output Voltage
n Programmable Input Voltage Comparator
n Programmable Current Limit
n Programmable Switching Frequency
n Programmable OV and UV Comparators
n Programmable On and Off Delay Times
n Programmable Output Rise/Fall Times
n Phase-Locked Loop for Synchronous, Polyphase Opera-
tion (2, 3, 4 or 6 Phases)
n Input and Output Voltage/Current, Temperature and
Duty Cycle Telemetry
n Fully Differential Load Sense
n Integrated Gate Drivers
n Non-Volatile Configuration Memory with ECC
n Optional External Configuration Resistors for Key
Operating Parameters
n Optional Time-Base Interconnect for Synchronization
Between Multiple Controllers
n Fault Logging
n WP Pin to Protect Internal Configuration
n Standalone Operation After User Factory Configuration
n PMBus, 400kHz Compliant Interface
The PMBus interface provides access to important power
management data during system operation including:
n Internal Controller Temperature
n External System Temperature via Optional Diode Sense
Elements
n Average Output Current
n Average PWM Duty Cycle
n Average Output Voltage
n Average Input Voltage
n Average Input Current
n Configurable, Latched and Unlatched Individual Fault
and Warning Status
Individual channels are accessed through the PMBus using
the PAGE command, i.e., PAGE 0 or 1.
Fault reporting and shutdown behavior are fully configu-
rable. Tw o individual GPIO outputs are provided (GPIO0,
GPIO1), both of which can be masked independently. A
dedicated pin for ALERT is provided. The shutdown opera-
tion also allows all faults to be individually masked and can
be operated in either unlatched (hiccup) or latched modes.
Individual status commands enable fault reporting over
the serial bus to identify the specific fault event. Fault or
warning detection includes the following:
n Output Undervoltage/Overvoltage
n Input Undervoltage/Overvoltage
n Input and Output Overcurrent
n Internal Overtemperature
n External Overtemperature
n Communication, Memory or Logic (CML) Fault
MAIN CONTROL LOOP
The LTC3880 is a constant frequency, current mode step-
down controller containing two channels operating with
various user-defined relative phasing. During normal
operation each top MOSFET is turned on when the clock
for that channel sets the RS latch, and turned off when
the main current comparator, ICMP
, resets the RS latch.
The peak inductor current at which ICMP resets the RS
latch is controlled by the voltage on the ITH pin which is
the output of each error amplifier, EA. The EA negative
terminal is equal to the VSENSE voltage divided by 5.5
(2.75 if range = 1). The positive terminal of the EA is
LTC3880/LTC3880-1
17
3880fg
For more information www.linear.com/LTC3880
OPERATION
connected to the output of a 12-bit DAC with values ranging
from 0V to 1.024V. The output voltage, through feedback
of the EA, will be regulated to 5.5 times the DAC output
(2.75 times if range = 1). The DAC value is calculated by
the part to synthesize the users desired output voltage.
The output voltage is programmed by the user either
with the resistor configuration pins detailed in Tables 12
and 13 or by the VOUT command (either from NVM or
by PMBus command). Refer to the PMBus command
section of the data sheet or the PMBus specification for
more details. The output voltage can be modified by the
user at any time with a PMBus VOUT_COMMAND. This
command will typically have a latency less than 10ms.
The user is encouraged to reference the PMBus Power
System Management Protocol Specification to understand
how to program the LTC3880. This specification can be
found at http://www.pmbus.org/specs.html.
Continuing the basic operation description, the current
mode controller will turn off the top gate when the peak
current is reached. If the load current increases, VSENSE
will slightly droop with respect to the DAC reference.
This causes the ITH voltage to increase until the average
inductor current matches the new load current. After the
top MOSFET has turned off, the bottom MOSFET is turned
on. In continuous conduction mode, the bottom MOSFET
stays on until the end of the switching cycle.
EEPROM
The LTC3880 contains internal EEPROM with Error Correc-
tion Coding (ECC) or NVM (nonvolatile memory) to store
configuration settings and fault log information. EEPROM
endurance retention and mass write operation time are
specified in the Electrical Characteristics and Absolute
Maximum Ratings sections. Write operations above TJ =
85°C are possible although the Electrical Characteristics
are not guaranteed and the EEPROM will be degraded.
Read operations performed at temperatures between
85°C and 125°C will not degrade the EEPROM. Writing
to the EEPROM above 85°C will result in a degradation of
retention characteristics. The fault logging function, which
is useful in debugging system problems that may occur
at high temperatures, only writes to fault log EEPROM
locations. If occasional writes to these registers occur
above 85°C, the slight degradation in the data retention
characteristics of the fault log will not take away from the
usefulness of the function.
It is recommended that the EEPROM not be written
when the die temperature is greater than 85°C. If the die
temperature exceeds 130°C, the LTC3880 will disable all
EEPROM write operations. All EEPROM write operations
will be re-enabled when the die temperature drops below
125°C. (The controller will also disable when the die
temperature exceeds the internal overtemperature fault
limit 160°C with a 10°C hysteresis)
The degradation in EEPROM retention for temperatures
>125°C can be approximated by calculating the dimen-
sionless acceleration factor using the following equation:
AF =e
Ea
k
⎛
⎝
⎜
⎜
⎞
⎠
⎟
⎟•1
TUSE +273–1
TSTR ESS +273
⎛
⎝
⎜
⎜
⎜
⎞
⎠
⎟
⎟
⎟
⎡
⎣
⎢
⎢
⎢
⎤
⎦
⎥
⎥
⎥
where:
AF = acceleration factor
Ea = activation energy = 1.4eV
K = 8.617 • 10–5 eV/°K
TUSE = 125°C specified junction temperature
TSTRESS = actual junction temperature in °C
Example: Calculate the effect on retention when operating
at a junction temperature of 135°C for 10 hours.
TSTRESS = 130°C
TUSE = 125°C
AF= e[(1.4/8.617 • 10–5) • (1/398 – 1/403)] = 1.66
The equivalent operating time at 125°C = 16.6 hours.
Thus the overall retention of the EEPROM was degraded
by 16.6 hours as a result of operating at a junction tem-
perature of 130°C for 10 hours. The effect of the overstress
is negligible when compared to the overall EEPROM
retention rating of 87,600 hours at a maximum junction
temperature of 125°C.
LTC3880/LTC3880-1
18
3880fg
For more information www.linear.com/LTC3880
OPERATION
POWER UP AND INITIALIZATION
The LTC3880 is designed to provide standalone supply
sequencing and controlled turn-on and turn-off opera-
tion. It operates from a single input supply (4.5V to 24V)
while three on-chip linear regulators generate internal
2.5V, 3.3V and 5V. If VIN is below 6V, the INTVCC and VIN
pins must be tied together. The controller configuration
is initialized by an internal threshold based UVLO where
VIN must be approximately 4V and the 5V, 3.3V and 2.5V
linear regulators must be within approximately 20% of
the regulated values. The LTC3880-1 does not have an
internal 5V linear regulators. The EXTVCC pin is driven by
an external regulator to improve efficiency of the circuit
and minimize power on the LTC3880. The EXTVCC pin
must exceed approximately 4V before the internal UVLO
is exceeded. To minimize application power, the EXTVCC
pin can be supplied by a switching regulator.
During initialization, the external configuration resistors
are identified and/or contents of the NVM are read into
the controller’s commands. The GPIOn pins are in high
impedance (Hi-Z) mode. The TGn, BGn and RUNn pins
are held low. The LTC3880 will use the contents of Tables
12 to 15 to determine the resistor defined parameters.
See the Resistor Configuration section for more detail.
The resistor configuration pins only control some of the
preset values of the controller. The remaining values are
programmed in NVM either at the factory or by the user.
If the configuration resistors are not inserted or if the
ignore RCONFIG bit is asserted (bit 6 of the MFR_
CONFIG_ALL_LTC3880 configuration command), the
LTC3880 will use only the contents of NVM to determine
the DC/DC characteristics. The ASEL value read at power-
up or reset is always respected unless the pin is open.
The ASEL will use the MSB from NVM and the LSB from
the detected threshold. See the Applications Information
section for more detail.
After the part has initialized, an additional comparator
monitors VIN. The VIN_ON threshold must be exceeded
before the output power sequencing can begin. After VIN
is initially applied, the part will typically require 120ms to
initialize and begin the TON_DELAY timer. The readback
of voltages and currents may require an additional 90ms.
SOFT-START
The part must enter the run state prior to soft-start.
The run pins are released by the LTC3880 after the part
initializes and VIN is greater than the VIN_ON threshold. If
multiple LTC3880s are used in an application, they all hold
their respective run pins low until all devices initialize and
VIN exceeds the VIN_ON threshold for every device. The
SHARE_CLK pin assures all the devices connected to the
signal use the same time base. The SHARE_CLK pin is held
low until the part has initialized after VIN is applied. The
LTC3880 can be set to turn off (or remain off) if SHARE_
CLK is low (set bit 2 of MFR_CHAN_CONFIG_LTC3880
to a 1). This allows the user to assure synchronization
across numerous LTC ICs even if the RUN pins can not be
connected together due to board constraints. In general, if
the user cares about synchronization between chips it is
best to connect all the respective RUN pins together and
to connect all the respective SHARE_CLK pins together.
This assures all chips begin sequencing at the same time
and use the same time base.
After the RUN pin releases and prior to entering a
constant output voltage regulation state, the LTC3880
performs a monotonic initial ramp or “soft-start”. Soft-
start is performed by actively regulating the load voltage
while digitally ramping the target voltage from 0V to the
commanded voltage set-point. Once the LTC3880 is
commanded to turn on, (after power up and initialization)
the controller waits for the user specified turn-on delay
(TON_DELAY) prior to initiating this output voltage ramp.
The rise time of the voltage ramp can be programmed
using the TON_RISE command to minimize inrush currents
associated with the start-up voltage ramp. The soft-start
feature is disabled by setting the value of TON_RISE to
any value less than 0.25ms. The LTC3880 PWM always
uses discontinuous mode during the TON_RISE operation.
In discontinuous mode, the bottom gate is turned off as
soon as reverse current is detected in the inductor. This
will allow the regulator to start up into a pre-biased load.
When the TON_MAX_FAULT_LIMIT is reached, the part
transitions to continuous mode or burst, if so programmed.
If TON_MAX_FAULT_LIMIT is set to zero, there is no time
limit and the part transitions to the desired conduction
mode after TON_RISE completes and VOUT has exceeded
LTC3880/LTC3880-1
19
3880fg
For more information www.linear.com/LTC3880
OPERATION
the VOUT_UV_FAULT_LIMIT and IOUT_OC is not present.
Setting TON_MAX_FAULT_LIMIT to a value of 0 is not
recommended. This described method of start-up se-
quencing is time based.
SEQUENCING
The default mode for sequencing the outputs on and off
is time based. Each output is enabled after waiting TON_
DELAY amount of time following either a RUN pin going
high, a PMBus command to turn on or the VIN rising above
a preprogrammed voltage. Off sequencing is handled in a
similar way. To assure proper sequencing, make sure all
ICs connect the SHARE_CLK pin together and RUN pins
together. If the RUN pins can not be connected together for
some reason, set bit 2 of MFR_CHAN_CONFIG_LTC3880
to a 1. This bit requires the SHARE_CLK pin to be clocking
before the power supply output can start. When the RUN pin
is pulled low, the LTC3880 will hold the pin low for the MFR_
RESTART_DELAY. The minimum MFR_RESTART_DELAY
is TOFF_DELAY + TOFF_FALL + 136ms. This delay assures
proper sequencing of all rails. The LTC3880 calculates
this delay internally and will not process a shorter delay.
However, a longer commanded MFR_RESTART_DELAY
will be used by the part. The maximum allowed value is
65.52 seconds.
VOLTAGE-BASED SEQUENCING
The GPIOn pins can be asserted when the UV threshold is
exceeded for each output. It is possible to feed the GPIO
pin from one output into the RUN pin of the next output
in the sequence. To use the GPIOn pin for voltage based
sequencing, set bit 12 of the MFR_GPIOn_PROPAGATE
command = 1. Bit 12 is the VOUT_UVUF (PGOOD) which is
the unfiltered VOUT_UV comparator. Using the unfiltered
VOUT_UV fault limit is recommended because there is little
appreciable time delay between the comparator crossing
the UV threshold and the GPIO pin releasing This can be
implemented across multiple LTC3880s. The VOUT_UVUF
(PGOOD) has a 70µs filter. If the VOUT voltage bounces
around the UV threshold for a long period of time it is
possible for the GPIO output to toggle more than once.
To minimize this problem, set the TON_RISE time under
100ms. If a fault in the string of rails is detected, only the
faulted rail and downstream rails will fault off. The rails in
the string of devices in front of the faulted rail will remain
on unless commanded off.
SHUTDOWN
The LTC3880 supports two shutdown modes. The first
mode is closed-loop shutdown response, with user-
defined turn-off delay (TOFF_DELAY) and ramp down
rate (TOFF_FALL). The controller will maintain the mode
of operation for TOFF_FALL. In discontinuous conduction
mode, the controller will not draw current from the load
and the fall time will be set by the output capacitance and
load current.
The other shutdown mode occurs in response to a fault
condition or loss of SHARE_CLK (if bit 2 of MFR_CHAN_
CONFIG_LTC3880 is set to a 1) or VIN falling below the
VIN_OFF threshold or GPIO pulled low externally (if the
MFR_GPIO_RESPONSE is set to inhibit). Under these
conditions the power stage is disabled in order to stop
the transfer of energy to the load as quickly as possible.
The shutdown state can be entered from the soft-start or
active regulation states either through user intervention
(deasserting RUNn or the PMBus OPERATION command)
or in response to a detected fault or an external fault via
the bidirectional GPIOn pins, or loss of SHARE_CLK (if
bit 2 of MFR_CHAN_CONFIG_LTC3880 is set to a 1) or
VIN falling below the VIN_OFF threshold.
In hiccup mode, the controller responds to a fault by
shutting down and entering the inactive state for a
programmable delay time (MFR_RETRY_DELAY).
LTC3880
Voltage Based Sequencing by Cascading GPIOs into RUN Pins
GPIO0 = VOUT0_UVUF
GPIO1 = VOUT1_UVUF
RUN 1
RUN 0
START
LTC3880
3880 F02
RUN 0 GPIO0 = VOUT0_UVUF
GPIO1 = VOUT1_UVUF
TO NEXT CHANNEL
IN THE SEQUENCE
RUN 1
Figure 2. Event (Voltage) Based Sequencing
LTC3880/LTC3880-1
20
3880fg
For more information www.linear.com/LTC3880
OPERATION
This delay minimizes the duty cycle associated with
autonomous retries if the fault that caused the shutdown
disappears once the output is disabled. The retry delay
time is determined by the longer of the MFR_RETRY_
DELAY command or the time required for the regulated
output to decay below 12.5% of the programmed value.
If multiple outputs are controlled by the same GPIO pin,
the decay time of the faulted output determines the retry
delay. If the natural decay time of the output is too long,
it is possible to remove the voltage requirement of the
MFR_RETRY_DELAY command by asserting bit 0 of
MFR_CHAN_CONFIG_LTC3880. Alternatively, the con-
troller can be configured so that it remains latched-off
following a fault and clearing requires user intervention
such as toggling RUNn or commanding the part OFF
then ON.
LIGHT LOAD CURRENT OPERATION
The LTC3880 has three modes of operation including high
efficiency Burst Mode operation, discontinuous conduction
mode or forced continuous conduction mode. Mode
selection is done using the MFR_PWM_MODE_LTC3880
command (discontinuous conduction is always the start-
up mode, forced continuous is the default running mode).
In Burst Mode operation the peak current in the inductor
is set to approximately one-third of the maximum sense
voltage even though the voltage on the ITH pin indicates a
lower value. If the average inductor current is higher than
the load current, the error amplifier, EA, will decrease the
voltage on the ITH pin. When the ITH voltage drops below
approximately 0.5V, the internal Burst Mode operation as-
serts and both external MOSFETs are turned off. In Burst
Mode operation, the load current is supplied by the output
capacitor. As the output voltage decreases, the EA output
begins to rise. When the output voltage drops sufficiently,
Burst Mode operation is deasserted, and the controller
resumes normal operation by turning on the top external
MOSFET on the next PWM cycle.
If a controller is enabled for Burst Mode operation, the
inductor current is not allowed to reverse. The reverse
current comparator, IREV
, turns off the bottom gate external
MOSFET just before the inductor current reaches zero,
preventing it from reversing and going negative. Thus,
the controller can operate in discontinuous operation.
In forced continuous operation, the inductor current is
allowed to reverse at light loads or under large transient
conditions. The peak inductor current is determined solely
by the voltage on the ITH pin. In this mode, the efficiency
at light loads is lower than in Burst Mode operation.
However, continuous mode exhibits lower output ripple and
less interference with audio circuitry. Forced continuous
conduction mode may result in reverse inductor current,
which can cause the input supply to boost. The VIN_OV_
FAULT_LIMIT can detect this and turn off the offending
channel. However, this fault is based on an ADC read and
can take up to 90ms to detect. If there is a concern about
the input supply boosting, keep the part in discontinuous
conduction or Burst Mode operation.
If the part is set to Burst Mode operation, as the inductor
average current increases, the controller will automati-
cally modify the operation from Burst Mode operation,
to discontinuous mode to continuous mode.
SWITCHING FREQUENCY AND PHASE
The switching frequency of the LTC3880’s controller can
be established with internal clock references or with an
external time-base. The LTC3880 can be configured for an
external clock input through the programmed value in NVM,
a PMBus command or setting the RBOTTOM resistor of the
FREQ_CFG pin to 0Ω and the RTOP to open. The PMBus
command FREQUENCY_SWITCH is set to external clock.
The MFR_PWM_CONFIG_LTC3880 command determines
the relative phasing. Using the RCONFIG input, channel 0
and channel 1 have a relative phasing of 0° and 180° with
respect to the falling edge of SYNC. The master should
be selected to be out of phase with the slave. Both RUN
pins must be low or both channels commanded off before
the FREQUENCY and MFR_PWM_CONFIG_LTC3880 com-
mands can be written to the LTC3880. The relative phas-
ing of all devices in a PolyPhase rail should be optimally
phased. The relative phasing of each rail is 360/n where
n is the number of phases in the rail.
If the LTC3880 is configured as the oscillator output on
SYNC, the switching frequency source can be selected with
LTC3880/LTC3880-1
21
3880fg
For more information www.linear.com/LTC3880
OPERATION
either external configuration resistors or through serial
bus programming. The FREQ_CFG configuration resistor
pin can be used to select the FREQUENCY_SWITCH
and MFR_PWM_CONFIG_LTC3880 values as outlined
in Table 14. Otherwise, the FREQUENCY_SWITCH and
MFR_PWM_CONFIG_LTC3880 PMBus commands can be
used to select PWM switching frequency and the PWM
channel phase relationship. The phase and frequency
relationships are completely independent of each other
providing the numerous application options for the user.
If the LTC3880 is configured to drive the SYNC pin using
the programmed FREQUENCY_SWITCH command value,
the SYNC pin will pull low at the desired clock rate with
500ns low pulse. Care must be taken in the application to
assure the capacitance on SYNC is minimized to assure
the pull-up resistor versus the capacitor load has a low
enough time constant for the application. In addition,
a phase-locked loop (PLL) is available to synchronize
the internal oscillator to an external clock source that is
connected to the SYNC pin. All phase relationships are
between the falling edge of SYNC and the rising edge
of the LTC3880 TG outputs. Multiple LTC3880s can be
synchronized in order to realize PolyPhase arrays.
OUTPUT VOLTAGE SENSING
The channel 0 differential amplifier allows remote, dif-
ferential sensing of the load voltage with VSENSE0n pins.
The channel 1 sense pin (VSENSE1) is referenced to SGND.
The telemetry ADC is fully differential and makes measure-
ments of channels 0 and 1 output voltages at the VSENSE0n
and VSENSE1/SGND pins, respectively. Due to head room
limitations of the internal amplifier for VSENSE0, the maxi-
mum allowed differential sense voltage is 4.096V.
CURRENT SENSING
For DCR current sense applications, a resistor in series
with a capacitor is placed across the inductor. In this
configuration, the resistor is tied to the FET side of the
inductor while the capacitor is tied to the load side of the
inductor as shown in Figure 3. If the RC values are cho-
sen such that the RC time constant matches the inductor
time constant (L/DCR, where DCR is the inductor series
resistance), the resultant voltage (VDCR) appearing across
the capacitor will equal the voltage across the inductor
series resistance and thus represent the current flowing
through the inductor. The RC calculations are based on
the room temperature DCR of the inductor.
Figure 3. Load Sharing Connections for 3-Phase Operation
LTC3880 + POWER STAGE
ITH0
1/2 LTC3880 + POWER STAGE
ITH0
VDD33
NOTE: SOME CONNECTORS
AND COMPONENTS OMITTED
FOR CLARITY
ISENSE0+
ISENSE0–
VSENSE0+
VSENSE0–
ITH1
10k
GPIO0
RUN0
RUN1
ALERT
GPIO1
SYNC
SHARE_CLK
VDD33
RUN0
ALERT
GPIO1
SYNC
SHARE_CLK
ISENSE0+
ISENSE0–
ISENSE1+
ISENSE1–
VSENSE1
PGNDSGND
1µF
PGND
3880 F03
SGND
VSENSE0+
VSENSE0–
1µF
LOAD
10k10k4.99k10k
RUN
SHARE_CLK
ALERT
GPIO
SYNC
LTC3880/LTC3880-1
22
3880fg
For more information www.linear.com/LTC3880
Figure 4. Temperature Sense Circuit
TSNS
MMBT3906
LTC3880 10nF
SGND
SGND 3880 F04
OPERATION
The RC time constant should remain constant, as a function
of temperature. This assures the transient response of
the circuit is the same regardless of the temperature. The
DCR of the inductor has a large temperature coefficient,
approximately 3900ppm/°C. The temperature coefficient
of the inductor must be written to the MFR_IOUT_CAL_
GAIN_TC register. The external temperature is sensed
near the inductor and used to modify the internal current
limit circuit to maintain an essentially constant current
limit with temperature. In this application, the ISENSEn+
pin is connected to the FET side of the capacitor while the
ISENSEn– pin is placed on the load side of the capacitor.
The current sensed from the input is then given by the
expression VDCR/DCR. VDCR is digitized by the LTC3880’s
telemetry ADC with an input range of ±128mV, a noise
floor of 7µVRMS, and a peak-peak noise of approximately
46.5µV. The LTC3880 computes the inductor current using
the DCR value stored in the IOUT_CAL_GAIN command
and the temperature coefficient stored in command
MFR_IOUT_CAL_GAIN_TC. The resulting current value
is returned by the READ_IOUT command.
LOAD SHARING
Multiple LTC3880’s can be arrayed in order to provide a
balanced load-share solution by bussing the necessary
pins. Figure 3 illustrates the shared connections required
for load sharing.
The frequency must only be programmed on one of the
LTC3880s. The other(s) must be programmed to External
Clock.
EXTERNAL/INTERNAL TEMPERATURE SENSE
External temperature can be best measured using a remote
diode-connected PNP transistor such as the MMBT3906.
The emitter should be connected to the TSNSn pin while the
base and collector terminals of the PNP transistor should
be returned to the LTC3880’s SGND pin, preferably using a
star connection. It is possible to connect the collector of the
PNP to the source of the bottom MOSFET. This may optimize
board layout allowing the PNP closer proximity to the power
FETs. The base of the PNP must still be tied to signal ground.
For best noise immunity, the connections should be routed
differentially and a 10nF capacitor should be placed in
parallel with the diode connected PNP. Two different currents
are applied to the diode (nominally 2µA and 32µA) and the
temperature is calculated from the ∆VBE measurement. The
external transistor temperature is digitized by the telemetry
ADC, and the value is returned by the PMBus READ_
TEMPERATURE_1 (Chn) command.
The READ_TEMPERATURE_2 command returns the
junction temperature of the LTC3880 using an on-chip
diode. The slope of the external temperature sensor can be
modified with the temperature slope coefficient stored in
MFR_TEMP_1_GAIN. Typical PNPs require temperature
slope adjustments slightly less than 1. The MMBT3906 has
a recommended value in this command of approximately
MFR_TEMP_1_GAIN = 0.991 based on the ideality factor
of 1.01. Simply invert the ideality factor to calculate the
MFR_TEMP_1_GAIN. Different manufacturers and differ-
ent lots may have different ideality factors. Consult with
the manufacturer to set this value.
The offset of the external temperature sense can be adjusted
by MFR_TEMP_1_OFFSET. A value of 0 in this register
sets the temperature offset to –273.15°C.
If the PNP cannot be placed in direct contact with the
inductor, the slope or offset can be increased to account
for temperature mismatches. If the user is adjusting the
slope, the intercept point is at absolute zero, –273.15°C,
so small adjustments in slope can change the apparent
measured temperature significantly. Another way to
artificially increase the slope of the temperature term is
to increase the MFR_IOUT_CAL_GAIN_TC term. This
will modify the temperature slope with respect to room
temperature.
LTC3880/LTC3880-1
23
3880fg
For more information www.linear.com/LTC3880
OPERATION
RCONFIG (RESISTOR CONFIGURATION) PINS
There are six input pins utilizing 1% resistor dividers between
VDD25 and SGND to select key operating parameters. The pins
are ASEL, FREQ_CFG, VOUT0_CFG, VOUT1_CFG, VTRIM0_CFG
and VTRIM1_CFG. If pins are floated, the value stored in
the corresponding NVM command is used. If bit 6 of the
MFR_CONFIG_ALL_LTC3880 configuration command is
asserted in NVM, the resistor inputs are ignored upon power-
up except for ASEL which is always respected. The resistor
configuration pins are only measured during a power-up
reset or after an MFR_RESET command is executed.
The VOUTn_CFG and VTRIMn pin settings are described in
Tables 12 and 13. These pins select the output voltages
for the LTC3880’s analog PWM controllers. If both pins
are open, the VOUT_COMMAND command is loaded from
NVM to determine the output voltage.
The following parameters are set as a percentage of the
output voltage if the RCONFIG pins are used to determined
output voltage:
n VOUT_OV_FAULT_LIMIT .................................... +10%
n VOUT_OV_WARN .............................................. +7.5%
n VOUT_MAX....................................................... +7.5%
n VOUT_MARGIN_HI ..............................................+5%
n POWER_GOOD_ON .............................................–7%
n POWER_GOOD_OFF ............................................–8%
n VOUT_MARGIN_LO .............................................–5%
n VOUT_UV_WARN ..............................................–6.5%
n VOUT_UV_FAULT_LIMIT ......................................–7%
The FREQ_CFG pin settings are described in Table 14. This
pin selects the switching frequency and phase relationships
between the two channels and SYNC pin. To synchronize to
an external clock, the part must be put into external clock
mode (FREQ_CFG pin shorted to ground). If no external
clock is supplied, the part will clock at the lowest free-
running frequency of the internal PWM oscillator. This low
clock rate will increase the ripple current of the inductor
possibly producing undesirable operation. If the external
SYNC signal is missing or misbehaving, a “PLL Lock Status”
fault will be indicated in the STATUS_MFR_SPECIFIC
command. If the user does not wish to see the PLL_FAULT
even if there is not a valid synchronization signal at power
up, bit 3 of the MFR_CONFIG_ALL_LT C 3880 command
must be asserted. If the SYNC pin is connected between
multiple ICs only one of the ICs can be the oscillator, all
other ICs must be configured to external clock.
The ASEL pin settings are described in Table 15. This
pin selects the bottom 4 bits of the slave address for the
LTC3880. The 3 most significant bits are retrieved from
the NVM MFR_ADDRESS command. If the pin is floating,
the 7-bit value stored in NVM MFR_ADDRESS command
is used to determine the slave address. For more detail,
refer to Table 15a.
Note: Per the PMBus specification, pin programmed
parameters can be overridden by commands from the
digital interface with the exception of ASEL which is
always honored. Do not set any part address to 0x5A or
0x5B because these are global addresses and all parts
will respond to them.
FAULT DETECTION AND HANDLING
A variety of fault and warning reporting and handling
mechanisms are available. Fault and warning detection
capabilities include:
n Input OV/FAULT Protection and UV Warning
n Average Input OC Warn
n Output OV/UV Fault and Warn Protection
n Output OC Fault and Warn Protection
n Internal and External Overtemperature Fault Protection
n External Undertemperature Fault and Warn Protection
n CML Fault (Communication, Memory or Logic)
n External Fault Detection via the Bidirectional GPIOn
Pins.
In addition, the LTC3880 can map any combination of fault
indicators to their respective GPIOn pin using the propagate
GPIOn response commands, MFR_GPIO_PROPAGATE_
LTC3880. Typical usage of a GPIO pin is as a driver for an
external crowbar device, overtemperature alert, overvoltage
alert or as an interrupt to cause a microcontroller to poll the
fault commands. Alternatively, the GPIOn pins can be used as
inputs to detect external faults downstream of the controller
that require an immediate response. The GPIO0 and/or
LTC3880/LTC3880-1
24
3880fg
For more information www.linear.com/LTC3880
OPERATION
GPIO1 pins can also be configured as power good outputs
(by asserting bit 12 of MFR_GPIO_PROPAGATE_LTC3880).
Power good indicates the controller output is above the UV
threshold. At power-up the pin will initially be three-state.
Traditionally PGOOD also includes the OV threshold. Assert bit
0 of MFR_GPIO_PROPAGATE_LTC3880 if this is desired. If it
is necessary to have the desired polarity on the pin at power-
up in this configuration, attach a Schottky diode between the
RUN pin of the propagated power good signal and the GPIO
pin. The Cathode must be attached to RUN and the Anode to
the GPIO pin. If the GPIO pin is set to a power good status,
the MFR_GPIO_RESPONSE must be ignore otherwise there
is a latched off condition with the controller.
As described in the Soft-Start section, it is possible to control
start-up through concatenated events. If GPIOn is used
to drive the RUN pin of another controller, the unfiltered
VOUT_UV fault limit (PGOOD) should be mapped to the
GPIO pin.
Any fault or warning event will cause the ALERT pin to
assert low. The pin will remain asserted low until the
CLEAR_FAULTS command is issued, the fault bit is written
to a 1 or bias power is cycled or a MFR_RESET command
is issued. Channel specific faults are cleared if the RUN
pins are toggled OFF/ON or the part is commanded OFF/ON
via PMBus. If bit 0 of MFR_CONFIG_ALL_LTC3880 is set
to a 1, toggling the RUN pins OFF/ON clears all faults. The
MFR_GPIO_PROPAGATE_LT C 3880 command determines
if the GPIO pins are pulled low when a fault is detected;
however, the ALERT pin is always pulled low if a fault or
warning is detected and the status bits are updated.
Output and input fault event handling is controlled by the
corresponding fault response byte as specified in Tables 5
to 9. Shutdown recovery from these types of faults can
either be autonomous or latched. For autonomous recovery,
the faults are not latched, so if the fault condition is not
present after the retry interval has elapsed, a new soft-
start is attempted. If the fault persists, the controller will
continue to retry. The retry interval is specified by the
MFR_RETRY_DELAY command and prevents damage
to the regulator components by repetitive power cycling,
assuming the fault condition itself is not immediately
destructive. The MFR_RETRY_DELAY must be greater
than 120ms. It can not exceed 83.88 seconds.
Channel-to-channel fault dependencies can be created by
connecting GPIOn pins together. In the event of an internal
fault, one or more of the channels is configured to pull
the bussed GPIOn pins low. The other channels are then
configured to shut down when the GPIOn pins are pulled
low. For autonomous group retry, the faulted channel
is configured to let go of the GPIOn pin(s) after a retry
interval, assuming the original fault has cleared. All the
channels in the group then begin a soft-start sequence. If
the fault response is LATCH_OFF, the GPIO pin remains
asserted low until either the RUN pin is toggled OFF/ON or
the part is commanded OFF/ON. The toggling of the RUN
either by the pin or OFF/ON command will clear faults
associated with the channel. If it is desired to have all faults
cleared when either RUN pin is toggled, set bit 0 of MFR_
CONFIG_ALL_LTC3880 to a 1.
The status of all faults and warnings is summarized in the
STATUS_WORD and STATUS_BYTE commands.
Additional fault detection and handling capabilities are:
Internal Memory with CRC and ECC
The LTC3880 contains internal EEPROM with error correc-
tion coding (ECC) to store user configuration settings and
fault log information. EEPROM endurance and retention for
user space and fault log pages are specified in the Absolute
Maximum Ratings and Electrical Characteristics table.
The integrity of the NVM memory is checked with a CRC
calculation each time its data is to be read, such as after
a power-on reset. A CRC failure will prevent the controller
from leaving the inactive state. If a CRC failure occurs, the
CML bit is set in the STATUS_BYTE and STATUS_WORD
commands, the appropriate bit is set in the STATUS_
MFR_SPECIFIC command, and the ALERT and RUN pins
will be pulled low. At that point, the device will respond
at special address 0x7C, which is only activated after an
invalid CRC has been detected. The chip will also respond
to global addresses 0x5A and 0x5B, but all LTC PSM chips
will respond to these addresses so users must be careful
when using global addresses. NVM repair can be attempted
LTC3880/LTC3880-1
25
3880fg
For more information www.linear.com/LTC3880
OPERATION
by writing the desired configuration to the controller and
executing a STORE_USER_ALL command followed by a
CLEAR_FAULTS command. Contact the factory if EEPROM
repair is unsuccessful.
See the Applications Information section or contact the
factory for details on efficient in-system EEPROM pro-
gramming, including bulk EEPROM programming, which
the LTC3880 also supports.
SERIAL INTERFACE
The LTC3880 serial interface is a PMBus compliant slave
device and can operate at any frequency between 10kHz
and 400kHz. The address is configurable using either the
NVM or an external resistor divider. In addition the LTC3880
always responds to the global broadcast address of 0x5A
(7 bit) or 0x5B (7 bit). Address 0x5A is not paged and
is performed on both channels. 0x5B respects the page
command. Because address 0x5A does not support page,
it can not be used for any paged reading commands.
The serial interface supports the following protocols defined
in the PMBus specifications: 1) send command, 2) write
byte, 3) write word, 4) group, 5) read byte, 6) read word
and 7) read block. All read operations will return a valid
PEC if the PMBus master requests it. If the PEC_REQUIRED
bit is set in the MFR_CONFIG_ALL_LT C 3880 command,
the PMBus write operations will not be acted upon until
a valid PEC has been received by the LTC3880.
Communication Failure
PEC write errors (if PEC_REQUIRED is active), attempts
to access unsupported commands, or writing invalid data
to supported commands will result in a CML fault. The
CML bit is set in the STATUS_BYTE and STATUS_WORD
commands, the appropriate bit is set in the STATUS_CML
command, and the ALERT pin is pulled low.
DEVICE ADDRESSING
The LTC3880 offers five different types of addressing over
the PMBus interface, specifically: 1) global, 2) device, 3)
channel, 4) rail addressing and 5) alert response address
(ARA).
Global addressing provides a means of the PMBus master
to address all LTC3880 devices on the bus. The LTC3880
global address is fixed 0x5A (7 bit) or 0xB4 (8 bit) and cannot
be disabled. Commands sent to the global address act the
same as if PAGE is set to a value of 0xFF. Commands sent are
written to both channels simultaneously. Global command
0x5B (7 bit) or 0xB6 (8 bit) is paged and allows channel
specific command of all LTC3880 devices on the bus.
Device addressing provides the standard means of the
PMBus master communicating with a single instance
of an LTC3880. The value of the device address is set
by a combination of the ASEL configuration pin and the
MFR_ADDRESS command. When this addressing means
is used, the PAGE command determines the channel being
acted upon. Device addressing can be disabled by writing
a value of 0x80 to the MFR_ADDRESS.
Channel addressing provides a means for the PMBus
master addressing a single channel of the LTC3880
without using the PAGE command. The value assigned
to the paged MFR_CHANNEL_ADDRESS determines the
specific channel the user wishes to act upon. Example: If
MFR_CHANNEL_ADDRESS for page 0 is set to 0x57 and
the MFR_CHANNEL_ADDRESS for page 1 is set to 0x54,
the user can address channel 0 of the device by performing
PMBus device commands using address 0x57 (7 bit). The
user can address channel 1 of the device by performing
PMBus device commands using address 0x54 (7 bit). This
eliminates the user from first assigning the PAGE command
and then the command to be acted upon.
Rail addressing provides a means for the PMBus master
addressing a set of channels connected to the same output
rail, simultaneously. This is similar to global addressing,
however, the PMBus address can be dynamically assigned
by using the MFR_RAIL_ADDRESS command. The MFR_
RAIL_ADDRESS is paged, so channels can be indepen-
dently assigned to a specific rail. It is recommended that rail
addressing should be limited to command write operations.
All five means of PMBus addressing require the user to
employ disciplined planning to avoid addressing conflicts.
LTC3880/LTC3880-1
26
3880fg
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OPERATION
RESPONSES TO VOUT AND IOUT FAULTS
VOUT OV and UV conditions are monitored by comparators.
The OV and UV limits are set in three ways.
n As a Percentage of the VOUT if Using the Resistor Con-
figuration Pins
n In NVM if Either Programmed at the Factory or Through
the GUI
n By PMBus Command
The IIN and IOUT overcurrent monitors are performed by
ADC readings and calculations. Thus these values are
based on average currents and can have a time latency of
up to 90ms. The IOUT calculation accounts for the sense
resistor and the temperature coefficient of the resistor.
The input current is equal to the sum of output current
times the respective channel duty cycle plus the input
offset current for each channel. If this calculated input
current exceed the IN_OC_WARN_LIMIT the ALERT pin
is pulled low and the IIN_OC_WARN bit is asserted in the
STATUS_INPUT register.
The digital processor within the LTC3880 provides the
ability to ignore the fault, shut down and latch off or shut
down and retry indefinitely (hiccup). The retry interval
is set in MFR_RETRY_DELAY and can be from 120ms
to 83.88 seconds in 1ms increments. The shutdown for
OV/UV and OC can be done immediately or after a user
selectable deglitch time.
Output Overvoltage Fault Response
A programmable overvoltage comparator (OV) guards
against transient overshoots as well as long-term over-
voltages at the output. In such cases, the top MOSFET is
turned off and the bottom MOSFET is turned on until the
overvoltage condition is cleared regardless of the PMBus
VOUT_OV_FAULT_RESPONSE command byte value. This
hardware level fault response delay is typically 2µs from
the overvoltage condition to BG asserted high. Using the
VOUT_OV_FAULT_RESPONSE command, the user can
select any of the following behaviors:
n OV Pull-Down Only (OV cannot be ignored)
n Shut Down (Stop Switching) Immediately—Latch Off
n Shut Down Immediately—Retry Indefinitely at the Time
Interval Specified in MFR_RETRY_DELAY
Either the Latch Off or Retry fault responses can be de-
glitched in increments of (0-7) • 10µs. See Table 5.
Output Undervoltage Response
The response to an undervoltage comparator output can
be either:
n Ignore
n Shut Down Immediately—Latch Off
n Shut Down Immediately—Retry Indefinitely at the Time
Interval Specified in MFR_RETRY_DELAY
The UV responses can be deglitched. See Table 6.
Peak Output Overcurrent Fault Response
Due to the current mode control algorithm, peak output
current across the inductor is always limited on a cycle by
cycle basis. The value of the peak current limit is specified
in sense voltage in the EC table. The current limit circuit
operates by limiting the ITH maximum voltage. If DCR sens-
ing is used, the ITH maximum voltage has a temperature
dependency directly proportional to the TC of the DCR of
the inductor. The LTC3880 automatically monitors the
external temperature sensors and modifies the maximum
allowed ITH to compensate for this term.
The overcurrent fault processing circuitry can execute the
following behaviors:
n Current Limit Indefinitely
n Shut Down Immediately—Latch Off
n Shut Down Immediately—Retry Indefinitely at the Time
Interval Specified in MFR_RETRY_DELAY
LTC3880/LTC3880-1
27
3880fg
For more information www.linear.com/LTC3880
OPERATION
The overcurrent responses can be deglitched in increments
of (0-7) • 16ms. See Table 7
RESPONSES TO TIMING FAULTS
TON_MAX_FAULT_LIMIT is the time allowed for VOUT to
rise and settle at start-up. The TON_MAX_FAULT_LIMIT
condition is predicated upon detection of the VOUT_UV_
FAULT_LIMIT as the output is undergoing a SOFT_START
sequence. The TON_MAX_FAULT_LIMIT time is started
after TON_DELAY has been reached and a SOFT_START
sequence is started. The resolution of the TON_MAX_
FAULT_LIMIT is 10µs. If the VOUT_UV_FAULT_LIMIT
is not reached within the TON_MAX_FAULT_LIMIT time,
the response of this fault is determined by the value of
the TON_MAX_FAULT_RESPONSE command value. This
response may be one of the following:
n Ignore
n Shut Down (Stop Switching) Immediately—Latch Off
n Shut Down Immediately—Retry Indefinitely at the Time
Interval Specified in MFR_RETRY_DELAY
This fault response is not deglitched. A value of 0 in
TON_MAX_FAULT_LIMIT means the fault is ignored. The
TON_MAX_FAULT_LIMIT should be set longer than the
TON_RISE time. It is recommended TON_MAX_FAULT_
LIMIT always be set to a non-zero value, otherwise the
output may never come up and no flag will be set to the
user.
See Table 9.
RESPONSES TO VIN OV FAULTS
VIN overvoltage is measured with the MUX’d ADC; therefore,
the response is naturally deglitched by the 90ms typical
response time of the ADC. The fault responses are:
n Ignore
n Shut Down Immediately—Latch Off
n Shut Down Immediately—Retry Indefinitely at the Time
Interval Specified in MFR_RETRY_DELAY
See Table 9.
RESPONSES TO OT/UT FAULTS
Overtemperature Fault Response—Internal
An internal temperature sensor protects against NVM
damage. Above 85°C, no writes to NVM are recommended.
Above 130°C, the part disables the NVM and does not
re-enable until the temperature has dropped to 120°C.
Temperature is measured by the ADC. Internal tempera-
ture faults cannot be ignored. Internal temperature limits
cannot be adjusted by the user.
See Table 9.
Overtemperature and Undertemperature
Fault Response—Externals
Two external temperature sensors can be used to sense
critical circuit elements like inductors and power MOSFETs.
The OT_FAULT_RESPONSE and UT_FAULT_RESPOSE
commands are used to determine the appropriate response
to an overtemperature and undertemperature condition,
respectively. If no external sense elements are used
(not recommended) set the UT_FAULT_RESPONSE to
ignore and set the UT_FAULT_LIMIT to –275°C.
The fault responses are:
n Ignore
n Shut Down Immediately—Latch Off
n Shut Down Immediately—Retry Indefinitely at the Time
Interval Specified in MFR_RETRY_DELAY
See Table 9.
RESPONSES TO EXTERNAL FAULTS
When either GPIOn pin is pulled low, the OTHER bit is set
in the STATUS_WORD command, the appropriate bit is set
in the STATUS_MFR_SPECIFC command, and the ALERT
pin is pulled low. Responses are not deglitched. Each
channel can be configured to ignore or shut down then
retry in response to its GPIOn pin going low by modifying
the MFR_GPIO_RESPONSE command. To avoid the ALERT
pin asserting low when GPIO is pulled low, assert bit 1 of
MFR_CHAN_CONFIG_LTC3880.
LTC3880/LTC3880-1
28
3880fg
For more information www.linear.com/LTC3880
OPERATION
FAULT LOGGING
The LTC3880 has fault logging capability. Data is logged
into memory in the order shown in Table 11. The data to
be stored in the fault log is being continuously stored in
internal volatile memory. When a fault event occurs, the
recording into internal volatile memory is halted, the fault
log information is available from the MFR_FAULT_LOG
command, and the contents of the internal memory are
copied into NVM. Fault logging is allowed at temperatures
above 85°C; however, retention of 10 years is not guaran-
teed. When the die temperature exceeds 130°C the fault
logging is delayed until the die temperature drops below
120°C. After the fault condition that created the fault log
event has been removed, clear the fault before the fault
log data is erased, or else the part will immediately issue
another fault log.
When the LTC3880 powers-up, it checks the NVM for a
valid fault log. If a valid fault log exists in NVM, the “Valid
Fault Log” bit in the STATUS_MFR_SPECIFIC command
will be set and an ALERT event will be generated. Also,
fault logging will be blocked until the LTC3880 has
received a MFR_FAULT_LOG_CLEAR command before
fault logging will be re-enabled.
The information is stored in EEPROM in the event of any fault
that disables the controller on either channel. An external
GPIOn pulling low will not trigger a fault logging event.
BUS TIMEOUT FAILURE
The LTC3880 implements a timeout feature to avoid hang-
ing the serial interface. The data packet timer begins at the
first START event before the device address write byte.
Data packet information must be completed within 25ms or
the LTC3880 will three-state the bus and ignore the given
data packet. Data packet information includes the device
address byte write, command byte, repeat start event
(if a read operation), device address byte read (if a read
operation), all data bytes and the PEC byte if applicable.
The LTC3880 allows longer PMBus timeouts for block
read data packets. This timeout is proportional to the
length of the block read. The additional block read timeout
applies primarily to the MFR_FAULT_LOG command. In
no circumstances will the timeout period be less than the
tTIMEOUT_SMB specification of 32ms (typical).
The user is encouraged to use as high a clock rate as
possible to maintain efficient data packet transfer between
all devices sharing the serial bus interface. The LTC3880
supports the full PMBus frequency range from 10kHz to
400kHz.
SIMILARITY BETWEEN PMBUS, SMBUS AND I2C
2-WIRE INTERFACE
The PMBus 2-wire interface is an incremental extension
of the SMBus. SMBus is built upon I2C with some minor
differences in timing, DC parameters and protocol. The
PMBus/SMBus protocols are more robust than simple I2C
byte commands because PMBus/SMBus provide time-outs
to prevent bus hangs and optional packet error checking
(PEC) to ensure data integrity. In general, a master device
that can be configured for I2C communication can be
used for PMBus communication with little or no change
to hardware or firmware. Repeat start (restart) is not
supported by all I2C controllers but is required for SMBus/
PMBus reads. If a general purpose I2C controller is used,
check that repeat start is supported.
For a description of the minor extensions and exceptions
PMBus makes to SMBus, refer to PMBus Specification
Part 1 Revision 1.1: Paragraph 5: Transport.
For a description of the differences between SMBus and
I2C, refer to System Management Bus (SMBus) Speci-
fication Version 2.0: Appendix B—Differences Between
SMBus and I2C.
LTC3880/LTC3880-1
29
3880fg
For more information www.linear.com/LTC3880
OPERATION
PMBUS SERIAL DIGITAL INTERFACE
The LTC3880 communicates with a host (master) using the
standard PMBus serial bus interface. The Timing Diagram,
Figure 5, shows the timing relationship of the signals on
the bus. The two bus lines, SDA and SCL, must be high
when the bus is not in use. External pull-up resistors or
current sources are required on these lines.
The LTC3880 is a slave device. The master can com-
municate with the LTC3880 using the following formats:
n Master transmitter, slave receiver
n Master receiver, slave transmitter
The following PMBus protocols are supported:
n Write Byte, Write Word, Send Byte
n Read Byte, Read Word, Block Read
n Alert Response Address
Figures 7-16 illustrate the aforementioned PMBus proto-
cols. All transactions support PEC (parity error check) and
GCP (group command protocol). The Block Read supports
255 bytes of returned data. For this reason, the PMBus
timeout may be extended when reading the fault log.
Figure 6 is a key to the protocol diagrams in this section.
PEC is optional.
A value shown below a field in the following figures is a
mandatory value for that field.
Figure 5. Timing Diagram
SDA
SCL
tHD(STA) tHD(DAT)
tSU(STA) tSU(STO)
tSU(DAT)
tLOW
tHD(SDA) tSP tBUF
START
CONDITION
STOP
CONDITION
REPEATED START
CONDITION
START
CONDITION
tr
tftr
tf
tHIGH 3880 F05
Figure 6. PMBus Packet Protocol Diagram Element Key
SLAVE ADDRESS DATA BYTEWr A A P
3880 F06
S
7
S START CONDITION
Sr REPEATED START CONDITION
Rd READ (BIT VALUE OF 1)
Wr WRITE (BIT VALUE OF 0)
x SHOWN UNDER A FIELD INDICATES THAT THAT
FIELD IS REQUIRED TO HAVE THE VALUE OF x
A ACKNOWLEDGE (THIS BIT POSITION MAY BE 0
FOR AN ACK OR 1 FOR A NACK)
P STOP CONDITION
PEC PACKET ERROR CODE
MASTER TO SLAVE
SLAVE TO MASTER
CONTINUATION OF PROTOCOL
81 1 1
x x
11
...
The data formats implemented by PMBus are:
n Master transmitter transmits to slave receiver. The
transfer direction in this case is not changed.
n Master reads slave immediately after the first byte. At
the moment of the first acknowledgment (provided by
the slave receiver) the master transmitter becomes a
master receiver and the slave receiver becomes a slave
transmitter.
n Combined format. During a change of direction within
a transfer, the master repeats both a start condition
and the slave address but with the R/W bit reversed.
In this case, the master receiver terminates the transfer
by generating a NACK on the last byte of the transfer
and a STOP condition.
Examples of these formats are shown in Figures 7-16.
LTC3880/LTC3880-1
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3880fg
For more information www.linear.com/LTC3880
Figure 7. Write Byte Protocol
Figure 8. Write Word Protocol
Figure 9. Write Byte Protocol with PEC
Figure 10. Write Word Protocol with PEC
OPERATION
Table 1. Data Format Terminology
PMBus
TERMINOLOGY MEANING
TERMINOLOGY FOR: SPECS,
GUI, APPLICATION NOTES
ABBREVIATIONS FOR
SUMMARY COMMAND TABLE
FOR MORE DETAIL REFER TO
THE DATA FORMAT SECTION
OF TABLE 2
Linear Linear Linear_5s_11s L11 Page 35
Linear (for Voltage
Related Commands)
Linear Linear_16u L16 Page 35
Direct Direct-Manufacturer
Customized
DirectMfr CF Page 35
Hex Hex I16
ASCII ASCII ASC
Register Fields Reg Reg
SLAVE ADDRESS COMMAND CODE DATA BYTEWr A A A P
3880 F07
S
7 8 81 1 1 1 11
SLAVE ADDRESS COMMAND CODE DATA BYTE LOWWr A A A P
3880 F08
S
7 8 8 1
DATA BYTE HIGH
81 1 1 1 11
A
SLAVE ADDRESS COMMAND CODE DATA BYTEWr A A A P
3880 F09
S
7 8 8 1
PEC
81 1 1 1 11
A
SLAVE ADDRESS COMMAND CODE DATA BYTE LOWWr A A A P
3880 F10
S
7 8 8 1
DATA BYTE HIGH
8
PEC
811 1 1 1 11
A A
LTC3880/LTC3880-1
31
3880fg
For more information www.linear.com/LTC3880
OPERATION
Figure 11. Send Byte Protocol
Figure 12. Send Byte Protocol with PEC
Figure 13. Read Word Protocol
Figure 14. Read Word Protocol with PEC
Figure 16. Read Byte Protocol with PEC
Figure 15. Read Byte Protocol
SLAVE ADDRESS Wr A A P
3880 F11
S
7 81 1 1 11
COMMAND CODE
SLAVE ADDRESS COMMAND CODE PECWr A A A P
3880 F12
S
7 8 81 1 1 1 11
SLAVE ADDRESS COMMAND CODE SLAVE ADDRESSWr A A A P
3880 F13
S
7 8 7 1
DATA BYTE LOW
8
DATA BYTE HIGH
811 1 1
Sr
1 1 11
A
1
Rd A
SLAVE ADDRESS COMMAND CODE SLAVE ADDRESSWr A A A PA
3880 F14
S
7 8 7 1
DATA BYTE LOW
8
DATA BYTE HIGH PEC
8 811 1 1 1 111
Sr
1
A
1
Rd A
SLAVE ADDRESS COMMAND CODE SLAVE ADDRESSWr A A Sr P
3880 F15
S
7 8 7 11
DATA BYTE
8 11 1 1 11 1
ARd A
SLAVE ADDRESS COMMAND CODE SLAVE ADDRESSWr A A Sr P
3880 F16
S
7 8 7 11
DATA BYTE
8 11 1 1 11 1
ARd A
1
A PEC
Refer to Figure 6 for a legend.
Handshaking features are included to ensure robust
system communication. Please refer to the PMBus Com-
munication and Command Processing subsection of the
Applications Information section for further details.
LTC3880/LTC3880-1
32
3880fg
For more information www.linear.com/LTC3880
PMBUS
COMMANDS
The following tables list supported PMBus commands and
manufacturer specific commands. A complete description
of these commands can be found in the “PMBus Power
System Mgt Protocol Specification – Part II – Revision
1.1”. Users are encouraged to reference this specification.
Exceptions or manufacturer specific implementations
are listed below in Table 2. Floating point values listed in
the “DEFAULT VALUE” column are either Linear 16-bit
Signed (PMBus Section 8.3.1) or Linear_5s_11s (PMBus
Section 7.1) format, whichever is appropriate for the com-
mand. All commands from 0xD0 through 0xFF not listed
in this table are implicitly reserved by the manufacturer.
Users should avoid blind writes within this range of com-
mands to avoid undesired operation of the part. All com-
mands from 0x00 through 0xCF not listed in this table are
implicitly not supported by the manufacturer. Attempting to
access non-supported or reserved commands may result
in a CML command fault event. All output voltage settings
and measurements are based on the VOUT_MODE setting
of 0x14. This translates to an exponent of 2–12.
If PMBus commands are received faster than they are be-
ing processed, the part may become too busy to handle
new commands. In these circumstances the part follows
the protocols defined in the PMBus Specification v1.1,
Part II, Section 10.8.7, to communicate that it is busy.
The part includes handshaking features to eliminate busy
errors and simplify error handling software while ensur-
ing robust communication and system behavior. Please
refer to the subsection titled PMBus Communication and
Command Processing in the Applications Information
section for further details.
COMMAND NAME
CMD
CODE DESCRIPTION TYPE PAGED
DATA
FORMAT UNITS NVM
DEFAULT
VALUE PAGE
PAGE 0x00 Channel or page currently selected for any
command that supports paging.
R/W Byte N Reg 0x00 63
OPERATION 0x01 Operating mode control. On/off, margin high and
margin low.
R/W Byte Y Reg Y 0x80 67
ON_OFF_CONFIG 0x02 RUN pin and PMBus bus on/off command
configuration.
R/W Byte Y Reg Y 0x1E 66
CLEAR_FAULTS 0x03 Clear any fault bits that have been set. Send Byte N NA 91
WRITE_PROTECT 0x10 Level of protection provided by the device
against accidental changes.
R/W Byte N Reg Y 0x00 63
STORE_USER_ALL 0x15 Store user operating memory to EEPROM. Send Byte N NA 101
RESTORE_USER_ALL 0x16 Restore user operating memory from EEPROM. Send Byte N NA 101
CAPABILITY 0x19 Summary of PMBus optional communication
protocols supported by this device.
R Byte N Reg 0xB0 90
VOUT_MODE 0x20 Output voltage format and exponent (2–12). R Byte Y
Reg
2–12
0x14
71
VOUT_COMMAND 0x21 Nominal output voltage set point. R/W Word Y L16 V Y 1.0
0x1000
72
VOUT_MAX 0x24 Upper limit on the commanded output voltage
including VOUT_MARGIN_HIGH.
R/W Word Y L16 V Y 4.096 ch0
0x4189
5.5 ch1
0x5800
71
VOUT_MARGIN_HIGH 0x25 Margin high output voltage set point. Must be
greater than VOUT_COMMAND.
R/W Word Y L16 V Y 1.05
0x10CD
72
VOUT_MARGIN_LOW 0x26 Margin low output voltage set point. Must be
less than VOUT_COMMAND.
R/W Word Y L16 V Y 0.95
0x0F33
72
VOUT_TRANSITION_RATE 0X27 Rate the output changes when VOUT
commanded to a new value.
R/W Word Y L11 V/ms Y 0.25
AA00
78
Table 2. Summary (Note: The Data Format abbreviations are detailed at the end of this table.)
PMBus
COMMAND SUMMARY
LTC3880/LTC3880-1
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3880fg
For more information www.linear.com/LTC3880
PMBus
COMMAND SUMMARY
COMMAND NAME
CMD
CODE DESCRIPTION TYPE PAGED
DATA
FORMAT UNITS NVM
DEFAULT
VALUE PAGE
FREQUENCY_SWITCH 0x33 Switching frequency of the controller. R/W Word N L11 kHz Y 350
0xFABC
69
VIN_ON 0x35 Input voltage at which the unit should start
power conversion.
R/W Word N L11 V Y 6.5
0xCB40
70
VIN_OFF 0x36 Input voltage at which the unit should stop
power conversion.
R/W Word N L11 V Y 6.0
0xCB00
70
IOUT_CAL_GAIN 0x38 The ratio of the voltage at the current sense pins
to the sensed current. For devices using a fixed
current sense resistor, it is the resistance value
in mΩ.
R/W Word Y L11 mΩ Y 1.8
0xBB9A
74
VOUT_OV_FAULT_LIMIT 0x40 Output overvoltage fault limit. R/W Word Y L16 V Y 1.1
0x119A
71
VOUT_OV_FAULT_
RESPONSE
0x41 Action to be taken by the device when an output
overvoltage fault is detected.
R/W Byte Y Reg Y 0xB8 81
VOUT_OV_WARN_LIMIT 0x42 Output overvoltage warning limit. R/W Word Y L16 V Y 1.075
0x1133
72
VOUT_UV_WARN_LIMIT 0x43 Output undervoltage warning limit. R/W Word Y L16 V Y 0.925
0x0ECD
73
VOUT_UV_FAULT_LIMIT 0x44 Output undervoltage fault limit. R/W Word Y L16 V Y 0.9
0x0E66
73
VOUT_UV_FAULT_
RESPONSE
0x45 Action to be taken by the device when an output
undervoltage fault is detected.
R/W Byte Y Reg Y 0xB8 82
IOUT_OC_FAULT_LIMIT 0x46 Output overcurrent fault limit. R/W Word Y L11 A Y 29.75
0xDBB8
75
IOUT_OC_FAULT_
RESPONSE
0x47 Action to be taken by the device when an output
overcurrent fault is detected.
R/W Byte Y Reg Y 0x00 84
IOUT_OC_WARN_LIMIT 0x4A Output overcurrent warning limit. R/W Word Y L11 A Y 20.0
0xDA80
76
OT_FAULT_LIMIT 0x4F External overtemperature fault limit. R/W Word Y L11 C Y 100.0
0xEB20
77
OT_FAULT_RESPONSE 0x50 Action to be taken by the device when an external
overtemperature fault is detected,
R/W Byte Y Reg Y 0xB8 86
OT_WARN_LIMIT 0x51 External overtemperature warning limit. R/W Word Y L11 C Y 85.0
0xEAA8
77
UT_FAULT_LIMIT 0x53 External undertemperature fault limit. R/W Word Y L11 C Y –40.0
0xE580
77
UT_FAULT_RESPONSE 0x54 Action to be taken by the device when an external
undertemperature fault is detected.
R/W Byte Y Reg Y 0xB8 86
VIN_OV_FAULT_LIMIT 0x55 Input supply overvoltage fault limit. R/W Word N L11 V Y 15.5
0xD3E0
70
VIN_OV_FAULT_
RESPONSE
0x56 Action to be taken by the device when an input
overvoltage fault is detected.
R/W Byte Y Reg Y 0x80 80
VIN_UV_WARN_LIMIT 0x58 Input supply undervoltage warning limit. R/W Word N L11 V Y 6.3
0xCB26
70
IIN_OC_WARN_LIMIT 0x5D Input supply overcurrent warning limit. R/W Word N L11 A Y 10.0
0xD280
75
POWER_GOOD_ON 0x5E Output voltage at or above which a power good
should be asserted.
R/W Word Y L16 V Y 0.93
0x0EE1
73
LTC3880/LTC3880-1
34
3880fg
For more information www.linear.com/LTC3880
PMBus
COMMAND SUMMARY
COMMAND NAME
CMD
CODE DESCRIPTION TYPE PAGED
DATA
FORMAT UNITS NVM
DEFAULT
VALUE PAGE
POWER_GOOD_OFF 0x5F Output voltage at or below which a power good
should be de-asserted.
R/W Word Y L16 V Y 0.92
0x0EB8
73
TON_DELAY 0x60 Time from RUN and/or Operation on to output
rail turn-on.
R/W Word Y L11 ms Y 0.0
0x8000
78
TON_RISE 0x61 Time from when the output starts to rise until the
output voltage reaches the VOUT commanded
value.
R/W Word Y L11 ms Y 8.0
0xD200
78
TON_MAX_FAULT_LIMIT 0x62 Maximum time from VOUT_EN on for VOUT to
cross the VOUT_UV_FAULT_LIMIT.
R/W Word Y L11 ms Y 10.00
0xD280
78
TON_MAX_FAULT_
RESPONSE
0x63 Action to be taken by the device when a TON_
MAX_FAULT event is detected.
R/W Byte Y Reg Y 0xB8 83
TOFF_DELAY 0x64 Time from RUN and/or Operation off to the start
of TOFF_FALL ramp.
R/W Word Y L11 ms Y 0.0
0x8000
79
TOFF_FALL 0x65 Time from when the output starts to fall until the
output reaches zero volts.
R/W Word Y L11 ms Y 8.00
0xD200
79
TOFF_MAX_WARN_LIMIT 0x66 Maximum allowed time, after TOFF_FALL
completed, for the unit to decay below 12.5%.
R/W Word Y L11 ms Y 150
0xF258
79
STATUS_BYTE 0x78 One byte summary of the unit’s fault condition. R/W Byte Y Reg NA 92
STATUS_WORD 0x79 Tw o byte summary of the unit’s fault condition. R/W Word Y Reg NA 92
STATUS_VOUT 0x7A Output voltage fault and warning status. R/W Byte Y Reg NA 93
STATUS_IOUT 0x7B Output current fault and warning status. R/W Byte Y Reg NA 93
STATUS_INPUT 0x7C Input supply fault and warning status. R/W Byte N Reg NA 94
STATUS_TEMPERATURE 0x7D External temperature fault and warning status for
READ_TEMERATURE_1.
R/W Byte Y Reg NA 94
STATUS_CML 0x7E Communication and memory fault and warning
status.
R/W Byte N Reg NA 95
STATUS_MFR_SPECIFIC 0x80 Manufacturer specific fault and state information. R/W Byte Y Reg NA 95
READ_VIN 0x88 Measured input supply voltage. R Word N L11 V NA 98
READ_IIN 0x89 Measured input supply current. R Word N L11 A NA 99
READ_VOUT 0x8B Measured output voltage. R Word Y L16 V NA 99
READ_IOUT 0x8C Measured output current. R Word Y L11 A NA 99
READ_TEMPERATURE_1 0x8D External diode junction temperature. This is the
value used for all temperature related processing,
including IOUT_CAL_GAIN.
R Word Y L11 C NA 99
READ_TEMPERATURE_2 0x8E Internal junction temperature. Does not affect
any other registers.
R Word N L11 C NA 99
READ_DUTY_CYCLE 0x94 Duty cycle of the top gate control signal. R Word Y L11 % NA 100
READ_POUT 0x96 Measured output power. R Word Y L11 W NA 100
PMBUS_REVISION 0x98 PMBus revision supported by this device.
Current revision is 1.1.
R Byte N Reg 0x11 90
MFR_ID 0x99 The manufacturer ID of the LTC3880 in ASCII. R String N ASC LTC 90
MFR_MODEL 0x9A Manufacturer part number in ASCII. R String N ASC LTC3880 90
MFR_SERIAL 0x9E Serial number of this specific unit. R Block N CF NA 90
MFR_VOUT_MAX 0xA5 Maximum allowed output voltage. R Word Y L16 V 4.096 CH0
5.5 CH1
73
USER_DATA_00 0xB0 OEM RESERVED. Typically used for part
serialization.
R/W Word N Reg Y NA 89
LTC3880/LTC3880-1
35
3880fg
For more information www.linear.com/LTC3880
PMBus
COMMAND SUMMARY
COMMAND NAME
CMD
CODE DESCRIPTION TYPE PAGED
DATA
FORMAT UNITS NVM
DEFAULT
VALUE PAGE
USER_DATA_01 0xB1 Manufacturer reserved for LTpowerPlay. R/W Word Y Reg Y NA 89
USER_DATA_02 0xB2 OEM RESERVED. Typically used for part
serialization.
R/W Word N Reg Y NA 89
USER_DATA_03 0xB3 A NVM word available for the user. R/W Word Y Reg Y 0x0000 89
USER_DATA_04 0xB4 A NVM word available for the user. R/W Word N Reg Y 0x0000 89
MFR_INFO 0xB6 Manufacturing specific information. R Word N Reg NA 98
MFR_EE_UNLOCK 0xBD Unlock user EEPROM for access by MFR_EE_
ERASE and MFR_EE_DATA commands.
R/W Byte N Reg NA 108
MFR_EE_ERASE 0xBE Initialize user EEPROM for bulk programming by
MFR_EE_DATA.
R/W Byte N Reg NA 108
MFR_EE_DATA 0xBF Data transferred to and from EEPROM using
sequential PMBus word reads or writes.
Supports bulk programming.
R/W Word N Reg NA 108
MFR_CHAN_CONFIG_
LTC 3880
0xD0 Configuration bits that are channel specific. R/W Byte Y Reg Y 0x1F 65
MFR_CONFIG_ALL_
LTC 3880
0xD1 Configuration bits that are common to all pages. R/W Byte N Reg Y 0x09 65
MFR_GPIO_PROPAGATE_
LTC 3880
0xD2 Configuration that determines which faults are
propagated to the GPIO pins.
R/W Word Y Reg Y 0x2993 87
MFR_PWM_MODE_
LTC 3880
0xD4 Configuration for the PWM engine of each
channel.
R/W Byte Y Reg Y 0xC2 68
MFR_GPIO_RESPONSE 0xD5 Action to be taken by the device when the GPIO
pin is externally asserted low.
R/W Byte Y Reg Y 0xC0 89
MFR_OT_FAULT_
RESPONSE
0xD6 Action to be taken by the device when an internal
overtemperature fault is detected.
R Byte N Reg 0xC0 85
MFR_IOUT_PEAK 0xD7 Report the maximum measured value of
READ_IOUT since last MFR_CLEAR_PEAKS.
R Word Y L11 A NA 100
MFR_CHANNEL_
ADDRESS
0xD8 Address to the PAGE activated channel. R/W Byte Y Reg Y 0x80 64
MFR_RETRY_DELAY 0xDB Retry interval during FAULT retry mode. R/W Word Y L11 ms Y 350
0xFABC
80
MFR_RESTART_DELAY 0xDC Minimum time the RUN pin is held low by the
LTC3880.
R/W Word Y L11 ms Y 500
0xFBE8
80
MFR_VOUT_PEAK 0xDD Maximum measured value of READ_VOUT since
last MFR_CLEAR_PEAKS.
R Word Y L16 V NA 100
MFR_VIN_PEAK 0xDE Maximum measured value of READ_VIN since
last MFR_CLEAR_PEAKS.
R Word N L11 V NA 100
MFR_TEMPERATURE_1_
PEAK
0xDF Maximum measured value of external
Temperature (READ_TEMPERATURE_1)
since last MFR_CLEAR_PEAKS.
R Word Y L11 C NA 100
MFR_CLEAR_PEAKS 0xE3 Clears all peak values. Send Byte N NA 91
MFR_PADS 0xE5 Digital status of the I/O pads. R Word N Reg NA 97
MFR_ADDRESS 0xE6 Sets the 7-bit I2C address byte. R/W Byte N Reg Y 0x4F 64
MFR_SPECIAL_ID 0xE7 Manufacturer code representing the LTC3880 R Word N Reg 402x 90
MFR_IIN_OFFSET 0xE9 Coefficient used to add to the input current to
account for the IQ of the part.
R/W Word Y L11 A Y 0.050
0X9333
74
LTC3880/LTC3880-1
36
3880fg
For more information www.linear.com/LTC3880
PMBus
COMMAND SUMMARY
Note 1: Commands indicated with Y indicate that these commands are
stored and restored using the STORE_USER_ALL and RESTORE_USER_
ALL commands, respectively.
Note 2: Commands with a default value of NA indicate “not applicable”.
Commands with a default value of FS indicate “factory set on a per part
basis”.
Note 3: The LTC3880 contains additional commands not listed in this
table. Reading these commands is harmless to the operation of the IC;
however, the contents and meaning of these commands can change
without notice.
Note 4: Some of the unpublished commands are read-only and will
generate a CML bit 6 fault if written.
Note 5: Writing to commands not published in this table is not permitted.
Note 6: The user should not assume compatibility of commands
between different parts based upon command names. Always refer to
the manufacturer’s data sheet for each part for a complete definition of a
command’s function.
LTC has made every reasonable attempt to keep command functionality
compatible between parts; however, differences may occur to address
product requirements.
COMMAND NAME
CMD
CODE DESCRIPTION TYPE PAGED
DATA
FORMAT UNITS NVM
DEFAULT
VALUE PAGE
MFR_FAULT_LOG_STORE 0xEA Command a transfer of the fault log from RAM to
EEPROM. This causes the part to behave as if a
channel has faulted off.
Send Byte N NA 103
MFR_FAULT_LOG_CLEAR 0xEC Initialize the EEPROM block reserved for fault
logging and clear any previous fault logging
locks.
Send Byte N NA 107
MFR_READ_IIN 0xED Measured input current per channel R Word Y L11 A NA 99
MFR_FAULT_LOG 0xEE Fault log data bytes. This sequentially retrieved
data is used to assemble a complete fault log.
R Block N Reg Y NA 103
MFR_COMMON 0xEF Manufacturer status bits that are common across
multiple LTC chips.
R Byte N Reg NA 97
MFR_COMPARE_USER_
ALL
0xF0 Compares current command contents with NVM. Send Byte N NA 101
MFR_TEMPERATURE_2_
PEAK
0xF4 Peak internal die temperature since last MFR_
CLEAR_PEAKS.
R Word N L11 C NA 100
MFR_PWM_CONFIG_
LTC 3880
0xF5 Set numerous parameters for the DC/DC
controller including phasing.
R/W Byte N Reg Y 0x10 68
MFR_IOUT_CAL_GAIN_TC 0xF6 Temperature coefficient of the current sensing
element.
R/W Word Y CF Y 3900
0x0F3C
74
MFR_TEMP_1_GAIN 0xF8 Sets the slope of the external temperature
sensor.
R/W Word Y CF Y 1.0
0x4000
76
MFR_TEMP_1_OFFSET 0xF9 Sets the offset of the external temperature
sensor with respect to –273.1°C
R/W Word Y L11 C Y 0.0
0x8000
76
MFR_RAIL_ADDRESS 0xFA Common address for PolyPhase outputs to
adjust common parameters.
R/W Byte Y Reg Y 0x80 64
MFR_RESET 0xFD Commanded reset without requiring a power
down.
Send Byte N NA 67
LTC3880/LTC3880-1
37
3880fg
For more information www.linear.com/LTC3880
*DATA FORMAT
L11 Linear_5s_11s PMBus data field b[15:0]
Value = Y • 2N
where N = b[15:11] is a 5-bit two’s complement integer and Y = b[10:0] is an 11-bit
two’s complement integer
Example:
For b[15:0] = 0x9807 = ‘b10011_000_0000_0111
Value = 7 • 2–13 = 854 • 10–6
From “PMBus Spec Part II: Paragraph 7.1”
L16 Linear_16u PMBus data field b[15:0]
Value = Y • 2N
where Y = b[15:0] is an unsigned integer and N = Vout_mode_parameter is a 5-bit two’s
complement exponent that is hardwired to –12 decimal
Example:
For b[15:0] = 0x4C00 = ‘b0100_1100_0000_0000
Value = 19456 • 2–12 = 4.75
From “PMBus Spec Part II: Paragraph 8.2”
Reg Register PMBus data field b[15:0] or b[7:0].
Bit field meaning is defined in detailed PMBus Command Register Description.
I16 Integer Word PMBus data field b[15:0]
Value = Y
where Y = b[15:0] is a 16 bit unsigned integer
Example:
For b[15:0] = 0x9807 = ‘b1001_1000_0000_0111
Value = 38919 (decimal)
CF Custom Format Value is defined in detailed PMBus Command Register Description.
This is often an unsigned or two’s complement integer scaled by an MFR specific
constant.
ASC ASCII Format A variable length string of text characters conforming to ISO/IEC 8859-1 standard.
PMBus
COMMAND SUMMARY
LTC3880/LTC3880-1
38
3880fg
For more information www.linear.com/LTC3880
APPLICATIONS INFORMATION
The Typical Application on the back page is a basic LTC3880
application circuit. The LTC3880 can be configured to use
either DCR (inductor resistance) sensing or low value
resistor sensing. The choice between the two current
sensing schemes is largely a design trade-off between
cost, power consumption and accuracy. DCR sensing
is becoming popular because it saves expensive current
sensing resistors and is more power efficient, especially
in high current applications. The LTC3880 can nominally
account for the temperature dependency of the DCR
sensing element. The accuracy of the current reading
and current limit are typically limited by the accuracy of
the DCR resistor (accounted for in the IOUT_CAL_GAIN
parameter of the LTC3880). Thus current sensing resistors
provide the most accurate current sense and limiting for the
application. Other external component selection is driven
by the load requirement, and begins with the selection of
RSENSE (if RSENSE is used) and inductor value. Next, the
power MOSFETs are selected. Then the input and output
capacitors are selected. Finally the current limit is selected.
All of these components and ranges are required to be
determined prior to calculating the external compensation
components. The current limit range is required because
the two ranges (25mV to 50mV vs 37.5mV to 70mV) have
different EA gains set with bit 7 of the MFR_PWM_MODE_
LTC3880 command. The voltage RANGE bit also modifies
the loop gain and impacts the compensation network set
with bits 5, 6 of MFR_PWM_CONFIG_LTC3880. All other
programmable parameters do not affect the loop gain,
allowing parameters to be modified without impact to the
transient response to load.
CURRENT LIMIT PROGRAMMING
The LTC3880 has two ranges of current limit programming
and a total of eight levels within each range. Refer to the
IOUT_OC_FAULT_LIMIT section of the PMBus commands.
Within each range the error amp gain is fixed, resulting in
constant loop gain. The LTC3880 will account for the DCR
of the inductor and automatically update the current limit
as the inductor temperature changes. The temperature
coefficient of the DCR is stored in the MFR_IOUT_TC
register.
For the best current limit accuracy, use the 75mV setting.
The 25mV setting will allow for the use of very low DCR
inductors or sense resistors, but at the expense of cur-
rent limit accuracy. Keep in mind this operation is on a
cycle-by-cycle basis and is only a function of the peak induc-
tor current. The average inductor current is monitored by
the ADC converter and can provide a warning if too much
average output current is detected. The overcurrent fault
is detected when the ITH voltage hits the maximum value.
The digital processor within the LTC3880 provides the
ability to either ignore the fault, shut down and latch off
or shut down and retry indefinitely (hiccup). Refer to the
overcurrent portion of the Operation section for more detail.
ISENSE+ AND ISENSE– PINS
The ISENSE+ and ISENSE– pins are the inputs to the current
comparators and the A/D. The common mode input voltage
range of the current comparators is 0V to 5.5V. Both the
SENSE pins are high impedance inputs with small base
currents typically less than 1µA. When the ISENSE pins
ramp up from 0V to 1.4V, the small base currents flow
out of the SENSE pins. When the ISENSE pins are greater
than 1.4V, the base currents flow into the ISENSE pins. The
high impedance inputs to the current comparators allow
accurate DCR sensing. Do not to float these pins during
normal operation.
Filter components mutual to the ISENSE lines should be
placed close to the IC. The positive and negative traces
should be routed differentially and Kelvin connected to
the current sense element, see Figure 17. A non-Kelvin
connection elsewhere can add parasitic inductance and
capacitance to the current sense element, degrading
the information at the sense terminals and making the
programmed current limit unpredictable. In a PolyPhase
system, poor placement of the sensing element will result in
sub-optimal current sharing between power stages. If DCR
sensing is used (Figure 18a), sense resistor R1 should be
placed close to the switching node to prevent noise from
Figure 17. Optimal Sense Line Placement
COUT
TO SENSE FILTER,
NEXT TO THE CONTROLLER
INDUCTOR OR RSENSE 3880 F17
LTC3880/LTC3880-1
39
3880fg
For more information www.linear.com/LTC3880
VIN VIN
INTVCC
BOOST
TG
SW
BG
PGND
FILTER COMPONENTS
PLACED NEAR SENSE PINS
ISENSE+
ISENSE–
SGND
LTC3880 VOUT
3880 F018b
CF • 2RF ≤ ESL/RS
POLE-ZERO
CANCELLATION
SENSE RESISTOR
PLUS PARASITIC
INDUCTANCE
RSESL
CF
RF
RF
VIN VIN
INTVCC
BOOST
TG
SW
BG
PGND
INDUCTOR
DCR
R3
OPTIONAL
[(R1 + R3)||R2] • C1 = IOUT_CAL_GAIN = DCR • R3 = R1
*PLACE C1 NEAR SENSE+, SENSE– PINS
C2 >1µF
L
ISENSE+
ISENSE–
SGND
LTC3880 VOUT
3880 F18a
R1
R2
2 • L
DCR
C1*
R2
R1 + R2 + R3
APPLICATIONS INFORMATION
The current comparator has a maximum threshold
VSENSE(MAX) determined by the ILIMIT setting. The input
common mode range of the current comparator is 0V to
5.5V (if VIN is greater than 6V). The current comparator
threshold sets the peak of the inductor current, yielding
a maximum average output current IMAX equal to the
peak value less half the peak-to-peak ripple current ∆IL.
To calculate the sense resistor value, use the equation:
RSENSE =
V
SENSE(MAX)
IMAX +∆IL
2
Due to possible PCB noise in the current sensing loop, the
AC current sensing ripple of ∆VSENSE = ∆IL • RSENSE also
needs to be checked in the design to get a good signal-to-
noise ratio. In general, for a reasonably good PCB layout,
a 15mV minimum ∆VSENSE voltage is recommended as
a conservative number to start with, either for RSENSE or
DCR sensing applications.
For previous generation current mode controllers, the
maximum sense voltage was high enough (e.g., 75mV for
the LTC1628/LTC3728 family) that the voltage drop across
the parasitic inductance of the sense resistor represented
a relatively small error. In the new highest current density
solutions; however, the value of the sense resistor can be
less than 1mΩ and the peak sense voltage can be less
than 20mV. In addition, inductor ripple currents greater
than 50% with operation up to 1MHz are becoming more
common. Under these conditions, the voltage drop across
the sense resistor’s parasitic inductance is no longer neg-
ligible. A typical sensing circuit using a discrete resistor is
shown in Figure 18b. In previous generations of control-
lers, a small RC filter placed near the IC was commonly
used to reduce the effects of the capacitive and inductive
noise coupled in the sense traces on the PCB. A typical
filter consists of two series 100Ω resistors connected to
a parallel 1000pF capacitor, resulting in a time constant
of 200ns.
This same RC filter with minor modifications, can be
used to extract the resistive component of the current
sense signal in the presence of parasitic inductance. For
example, Figure 19 illustrates the voltage waveform across
a 2mΩ resistor with a 2010 footprint. The waveform is
Figure 18a. Inductor DCR Current Sense Circuit
Figure 18b. Resistor Current Sense Circuit
coupling into sensitive small-signal nodes. The capacitor
C1 should be placed close to the IC pins. This impedance
difference can result in loss of accuracy in the current
reading of the ADC. The current reading accuracy can be
improved by matching the impedance of the two pins. To
accomplish this add a series resistor between VOUT and
ISENSE– equal to R1. A capacitor of 1µF or greater should
be placed in parallel with this resistor. If the peak voltage
is <75mV at room temperature, R2 is not required.
LOW VALUE RESISTOR CURRENT SENSING
A typical sensing circuit using a discrete resistor is shown
in Figure 18b. RSENSE is chosen based on the required
output current.
LTC3880/LTC3880-1
40
3880fg
For more information www.linear.com/LTC3880
APPLICATIONS INFORMATION
the superposition of a purely resistive component and a
purely inductive component. It was measured using two
scope probes and waveform math to obtain a differential
measurement. Based on additional measurements of the
inductor ripple current and the on-time and off-time of
the top switch, the value of the parasitic inductance was
determined to be 0.5nH using the equation:
ESL =
V
ESL(STEP)
∆IL
•tON • tOFF
tON +tOFF
(1)
If the RC time constant is chosen to be close to the para-
sitic inductance divided by the sense resistor (L/R), the
resultant waveform looks resistive, as shown in Figure 20.
For applications using low maximum sense voltages,
check the sense resistor manufacturer’s data sheet for
information about parasitic inductance. In the absence
of data, measure the voltage drop directly across the
sense resistor to extract the magnitude of the ESL step
and use Equation 1 to determine the ESL. However, do
not overfilter the signal. Keep the RC time constant less
than or equal to the inductor time constant to maintain a
sufficient ripple voltage on VRSENSE for optimal operation
of the current loop controller.
INDUCTOR DCR CURRENT SENSING
For applications requiring the highest possible efficiency
at high load currents, the LTC3880 is capable of sensing
the voltage drop across the inductor DCR, as shown in
Figure 18a. The DCR of the inductor represents the small
amount of DC winding resistance of the copper, which
can be less than 1mΩ for today’s low value, high current
inductors. In a high current application requiring such an
inductor, conduction loss through a sense resistor would
cost a few points of efficiency compared to DCR sensing.
If the external (R1+R3)||R2 • C1 time constant is chosen to
be exactly equal to the 2 • L/DCR time constant, assuming
R1=R3, the voltage drop across the external capacitor is
equal to the drop across the inductor DCR multiplied by
R2/(R1+R2+R3). R2 scales the voltage across the sense
terminals for applications where the DCR is greater than the
target sense resistor value. The DCR value is entered as the
IOUT_CAL_GAIN in mΩ unless R2 is required. If R2 is used,
IOUT_CAL_GAIN = DCR • R2/(R1+R2+R3). If there is no
need to attenuate the signal, R2 can be removed. To properly
dimension the external filter components, the DCR of the
inductor must be known. It can be measured using a good
RLC meter, but the DCR tolerance is not always the same
and varies with temperature. Consult the manufacturers’ data
sheets for detailed information. The LTC3880 will account
for temperature variation if the correct parameter is entered
into the MFR_IOUT_CAL_GAIN_TC register. Typically the
resistance has a 3900ppm/°C coefficient.
C2 can be optimized for a flat frequency response, assum-
ing R1 = R3 by the following equation
C2 = [2R1 • R2 • C1–L/DCR • (2R1+R2)]/R12
Using the inductor ripple current value from the inductor
Value Calculation section, the target sense resistor value is:
RSENSE(EQUIV) =
V
SENSE(MAX)
IMAX +∆IL
2
To ensure that the application will deliver full load current
over the full operating temperature range, be sure to pick
the optimum ILIMIT value accounting for errors in the DCR
versus the MFR_IOUT_CAL_GAIN parameter entered.
Figure 19. Voltage Measured Directly Across RSENSE
Figure 20. Voltage Measured After the RSENSE Filter
500ns/DIV
VSENSE
20mV/DIV
3880 F19
VESL(STEP)
500ns/DIV
VSENSE
20mV/DIV
3880 F20
LTC3880/LTC3880-1
41
3880fg
For more information www.linear.com/LTC3880
APPLICATIONS INFORMATION
Next, determine the DCR of the inductor. Where provided,
use the manufacturer’s maximum value, usually given
at 20°C. Increase this value to account for errors in the
temperature sensing element of 3°C to 5°C and any
additional errors associated with the proximity of the
temperature sensor element to the inductor.
To scale the maximum inductor DCR to the desired sense
resistor value, use the divider ratio:
RD =RSENSE(EQUIV)
DCR(MAXERROR) at TL(MAX)
C1 is usually selected to be in the range of 0.047µF to
4.7µF. This forces R1||R2 to be approximately 2k. This
resistance minimizes errors caused by the SENSE pin
leakage currents. Adding optional elements R3 and C2
shown in Figure 18a will minimize offset errors associated
with these leakage currents.
The equivalent resistance (R1+R3)||R2 is scaled to the
room temperature inductance and maximum DCR:
(R1+R3) || R2 =
2 • L
DCR at 20°C
( )
• C1
The sense resistor values are:
R1=R3; R1=R1||R2
RD
; R2 =R1•RD
1– RD
The maximum power loss in R1 is related to the duty
cycle, and will occur in continuous mode at the maximum
input voltage:
PLOSS R1=VIN(MAX) – VOUT
( )
• VOUT
R1
Ensure that R1 has a power rating higher than this value.
If high efficiency is necessary at light loads, consider this
power loss when deciding whether to use DCR sensing or
sense resistors. Light load power loss can be modestly
higher with a DCR network than with a sense resistor
due to the extra switching losses incurred through R1.
However, DCR sensing eliminates a sense resistor, reduc-
ing conduction losses and provides higher efficiency at
heavy loads. Peak efficiency is about the same with either
method. Selecting Burst Mode operation or discontinuous
mode will improve the converter efficiency at light loads
regardless of the current sensing method.
To maintain a good signal-to-noise ratio for the current
sense signal, use a minimum ∆VSENSE of 10mV to 15mV.
For a DCR sensing application, the actual ripple voltage
will be determined by the equation:
∆VSENSE =
V
IN
– V
OUT
R1•C1 •
V
OUT
VIN • fOSC
SLOPE COMPENSATION AND INDUCTOR PEAK
CURRENT
Slope compensation provides stability in constant
frequency current mode architectures by preventing
sub-harmonic oscillations at high duty cycles. This is
accomplished internally by adding a compensation ramp
to the inductor current signal at duty cycles in excess of
35%. The LTC3880 uses a patented current limit technique
that counteracts the compensating ramp. This allows the
maximum inductor peak current to remain unaffected
throughout all duty cycles.
INDUCTOR VALUE CALCULATION
Given the desired input and output voltages, the inductor
value and operating frequency, fOSC, directly determine
the inductor peak-to-peak ripple current:
IRIPPLE =VOUT VIN – VOUT
( )
VIN • fOSC •L
Lower ripple current reduces core losses in the inductor,
ESR losses in the output capacitors, and output voltage
ripple. Thus, highest efficiency operation is obtained at the
lowest frequency with a small ripple current. Achieving
this, however, requires a large inductor.
A reasonable starting point is to choose a ripple current
that is about 40% of IOUT(MAX). Note that the largest ripple
current occurs at the highest input voltage. To guarantee
that the ripple current does not exceed a specified maxi-
mum, the inductor should be chosen according to:
L≥VOUT VIN – VOUT
( )
V
IN
• f
OSC
•I
RIPPLE
LTC3880/LTC3880-1
42
3880fg
For more information www.linear.com/LTC3880
APPLICATIONS INFORMATION
INDUCTOR CORE SELECTION
Once the inductor value is determined, the type of induc-
tor must be selected. Core loss is independent of core
size for a fixed inductor value, but it is very dependent
on inductance. As the inductance increases, core losses
go down. Unfortunately, increased inductance requires
more turns of wire and therefore copper losses increase.
Ferrite designs have very low core loss and are preferred
at high switching frequencies, so design goals can con-
centrate on copper loss and preventing saturation. Ferrite
core materials saturate hard, which means that the induc-
tance collapse abruptly when the peak design current is
exceeded. This results in an abrupt increase in inductor
ripple current and consequent output voltage ripple. Do
not allow the core to saturate!
POWER MOSFET AND SCHOTTKY DIODE (OPTIONAL)
SELECTION
Two external power MOSFETs must be selected for each
controller in the LTC3880: one N-channel MOSFET for
the top (main) switch, and one N-channel MOSFET for
the bottom (synchronous) switch.
The peak-to-peak drive levels are set by the INTVCC volt-
age. This voltage is typically 5V. Consequently, logic-level
threshold MOSFETs must be used in most applications.
The only exception is if low input voltage is expected (VIN
< 5V); then, sub-logic level threshold MOSFETs (VGS(TH)
< 3V) should be used. Pay close attention to the BVDSS
specification for the MOSFETs as well; most of the logic-
level MOSFETs are limited to 30V or less.
Selection criteria for the power MOSFETs include the on-
resistance, RDS(ON), Miller capacitance, CMILLER, input
voltage and maximum output current. Miller capacitance,
CMILLER, can be approximated from the gate charge curve
usually provided on the MOSFET manufacturers’ data
sheet. CMILLER is equal to the increase in gate charge
along the horizontal axis while the curve is approximately
flat divided by the specified change in VDS. This result is
then multiplied by the ratio of the application applied VDS
to the gate charge curve specified VDS. When the IC is
operating in continuous mode the duty cycles for the top
and bottom MOSFETs are given by:
Main Switch Duty Cycle =VOUT
VIN
Synchronous Switch Duty Cycle =VIN – VOUT
V
IN
The MOSFET power dissipations at maximum output
current are given by:
PMAIN =
V
OUT
VIN
IMAX
( )
21+ d
( )
RDS(ON) +
VIN
( )
2IMAX
2
⎛
⎝
⎜
⎜
⎞
⎠
⎟
⎟RDR
( )
CMILLER
( )
•
1
VINTVCC – VTH(MIN)
+1
VTH(MIN)
⎡
⎣
⎢
⎢
⎢
⎤
⎦
⎥
⎥
⎥• fOSC
PSYNC =VIN – VOUT
VIN
IMAX
( )
21+ d
( )
RDS(ON)
where d is the temperature dependency of RDS(ON) and
RDR (approximately 2Ω) is the effective driver resistance
at the MOSFET’s Miller threshold voltage. VTH(MIN) is the
typical MOSFET minimum threshold voltage.
Both MOSFETs have I2R losses while the topside N-channel
equation includes an additional term for transition losses,
which are highest at high input voltages. For VIN < 20V
the high current efficiency generally improves with larger
MOSFETs, while for VIN > 20V the transition losses rapidly
increase to the point that the use of a higher RDS(ON) device
with lower CMILLER actually provides higher efficiency. The
synchronous MOSFET losses are greatest at high input
voltage when the top switch duty factor is low or during
a short-circuit when the synchronous switch is on close
to 100% of the period.
The term (1 + d) is generally given for a MOSFET in the
form of a normalized RDS(ON) vs Temperature curve, but
d = 0.005/°C can be used as an approximation for low
voltage MOSFETs.
LTC3880/LTC3880-1
43
3880fg
For more information www.linear.com/LTC3880
APPLICATIONS INFORMATION
The optional Schottky diodes conduct during the dead time
between the conduction of the two power MOSFETs. These
prevent the body diodes of the bottom MOSFETs from turn-
ing on, storing charge during the dead time and requiring
a reverse recovery period that could cost as much as 3%
in efficiency at high VIN. A 1A to 3A Schottky is generally
a good compromise for both regions of operation due to
the relatively small average current. Larger diodes result
in additional transition losses due to their larger junction
capacitance.
VARIABLE DELAY TIME, SOFT-START AND OUTPUT
VOLTAGE RAMPING
The LTC3880 must enter the run state prior to soft-start.
The RUN pins are released after the part initializes and VIN
is greater than the VIN_ON threshold. If multiple LTC3880s
are used in an application, they should be configured to
share the same RUN pins. They all hold their respective
RUN pins low until all devices initialize and VIN exceeds
the VIN_ON threshold for all devices. The SHARE_CLK
pin assures all the devices connected to the signal use
the same time base.
After the RUN pin releases, the controller waits for the
user-specified turn-on delay (TON_DELAY) prior to
initiating an output voltage ramp. Multiple LTC3880s and
other LTC parts can be configured to start with variable
delay times. To work correctly, all devices use the same
timing clock (SHARE_CLK) and all devices must share
the RUN pin. This allows the relative delay of all parts
to be synchronized. The actual variation in the delay will
be dependent on the highest clock rate of the devices
connected to the SHARE_CLK pin (all Linear Technology
ICs are configured to allow the fastest SHARE_CLK signal
to control the timing of all devices). The SHARE_CLK signal
can be ±10% in frequency, thus the actual time delays will
have some variance.
Soft-start is performed by actively regulating the load
voltage while digitally ramping the target voltage from 0V
to the commanded voltage set point. The rise time of the
voltage ramp can be programmed using the TON_RISE
command to minimize inrush currents associated with the
start-up voltage ramp. The soft-start feature is disabled
by setting TON_RISE to any value less than 0.250ms.
The LTC3880 will perform the necessary math internally
to assure the voltage ramp is controlled to the desired
slope. However, the voltage slope can not be any faster
than the fundamental limits of the power stage. The shorter
TON_RISE time is set, the more jagged the TON_RISE ramp
will appear. The number of steps in the ramp is equal to
TON_RISE/0.1ms.
The LTC3880 PWM will always use discontinuous mode
during the TON_RISE operation. In discontinuous mode,
the bottom gate is turned off as soon as reverse current
is detected in the inductor. This will allow the regulator
to start up into a pre-biased load.
There is no tracking feature in the LTC3880; however,
two outputs can be given the same TON_RISE and
TON_DELAY times to effectively ramp up at the same time.
Because the RUN pins are released at the same time and
both units use the same time base, the outputs will track
very closely. If the circuit is in a PolyPhase configuration,
all timing parameters must be the same.
The described method of start-up sequencing is time based.
For concatenated events it is possible to control the RUN
pin based on the GPIO pin of a different controller. The
GPIO pin can be configured to release when the output
voltage of the converter is greater than the VOUT_UV_
FAULT_LIMIT. It is recommended to use the unfiltered
VOUT UV fault limit because there is little appreciable time
delay between the converter crossing the UV threshold
and the GPIO pin releasing. The unfiltered output can be
enabled using the MFR_GPIO_PROPAGATE_VOUT_UVUF
(PGOOD) command. (Refer to the MFR section of the
PMBus commands in this document). The unfiltered signal
may have some glitching as the VOUT signal transitions
through the comparator threshold. A small internal digital
filter of 70µs has been added to minimize this problem.
To minimize the risk of GPIO pins glitching, make the
TON_RISE times less than 100ms. If unwanted transitions
still occur on GPIO, place a capacitor to ground on the
GPIO pin to filter the waveform. The RC time-constant
of the filter should be set sufficiently fast to assure no
appreciable delay is incurred. A value of 300µs to 500µs
will provide some additional filtering without significantly
delaying the trigger event.
LTC3880/LTC3880-1
44
3880fg
For more information www.linear.com/LTC3880
APPLICATIONS INFORMATION
DIGITAL SERVO MODE
For maximum accuracy in the regulated output voltage,
enable the digital servo loop by asserting bit 6 of the
MFR_PWM_MODE_LTC3880 command. In digital servo
mode, the LTC3880 will adjust the regulated output voltage
based on the ADC voltage reading. Every 90ms the digital
servo loop will step the LSB of the DAC (nominally 1.375mV
or 0.6875mV depending on the voltage range bit) until the
output is at the correct ADC reading. At power-up this mode
engages after TON_MAX_FAULT_LIMIT unless the limit is
set to 0 (infinite). If the TON_MAX_FAULT_LIMIT is set to
0 (infinite), the servo begins after TON_RISE is complete
and VOUT has exceeded the VOUT_UV_FAULT_LIMIT and
IOUT_OC is not present. This same point in time is when
the output changes from discontinuous to the programmed
mode as indicated in MFR_PWM_MODE_LTC3880 bits 0
and 1. Refer to Figure 21 for details on the VOUT waveform
under time based sequencing.
If the TON_MAX_FAULT_IMIT is set to a value greater
than 0 and the TON_MAX_FAULT_RESPONSE is not set
to ignore 0X00, the servo begins:
1. After the TON_RISE sequence is complete;
2. After the TON_MAX_FAULT_LIMIT time has expired
and both VOUT_UV_FAULT and IOUT_OC_FAULT are
not present.
The maximum rise time is limited to 1.3 seconds.
In a PolyPhase configuration it is recommended only one
of the control loops have the digital servo mode enabled.
This will assure the various loops do not work against each
other due to slight differences in the reference circuits.
SOFT OFF (SEQUENCED OFF)
In addition to a controlled start-up, the LTC3880 also
supports controlled turn-off. The TOFF_DELAY and
TOFF_FALL functions are shown in Figure 22. TOFF_FALL
is processed when the RUN pin goes low or if the part
is commanded off. If the part faults off or GPIO is pulled
low externally and the part is programmed to respond to
this, the output will three-state rather than exhibiting a
controlled ramp. The output will decay as a function of
the load.
The output voltage will operate as shown in Figure 22 so
long as the part is in forced continuous mode and the
TOFF_FALL time is sufficiently slow that the power stage
can achieve the desired slope. The TOFF_FALL time can
only be met if the power stage and controller can sink
Figure 21. Timing Controlled VOUT Rise
Figure 22. TOFF_DELAY and TOFF_FALL
DAC VOLTAGE
ERROR (NOT
TO SCALE)
TIME DELAY OF
200ms - 400ms
DIGITAL SERVO
MODE ENABLED FINAL OUTPUT
VOLTAGE REACHED
TON_MAX_FAULT_LIMIT
TON_RISE TIME 3880 F21
TON_DELAY
VOUT
RUN
VOUT_UV_FAULT_LIMIT
TOFF_FALLTOFF_DELAY TIME 3880 F22
VOUT
RUN
If the TON_MAX_FAULT_LIMIT is set to a value greater
than 0 and the TON_MAX_FAULT_RESPONSE is set to
ignore 0x00, the servo begins:
1. After the TON_RISE sequence is complete
2. After the TON_MAX_FAULT_LIMIT time is reached; and
3. After the VOUT_UV_FAULT_LIMIT has been exceed or
the IOUT_OC_FAULT_LIMIT is not longer active.
LTC3880/LTC3880-1
45
3880fg
For more information www.linear.com/LTC3880
APPLICATIONS INFORMATION
sufficient current to assure the output is a zero volts by
the end of the fall time interval. If the TOFF_FALL time is
set shorter than the time required to discharge the load
capacitance, the output will not reach the desired zero volt
state. At the end of TOFF_FALL, the controller will cease
to sink current and VOUT will decay at the natural rate
determined by the load impedance. If the controller is in
discontinuous mode, the controller will not pull negative
current and the output will be pulled low by the load, not
the power stage. The maximum fail time is limited to 1.3
seconds. The shorter TOFF_FALL time is set, the more
jagged the TOFF_FALL ramp will appear. The number of
steps in the ramp is equal to TOFF_FALL/0.1ms.
INTVCC REGULATOR
The LTC3880 features an NPN linear regulator that sup-
plies power to INTVCC from the VIN supply. INTVCC powers
the gate drivers, VDD33 and much of the LTC3880 internal
circuitry. The linear regulator produces the voltage at the
INTVCC pin to nominally 5V when VIN is greater than 6.5V.
The regulator can supply a peak current of 100mA and must
be bypassed to ground with a minimum of 1µF ceramic
capacitor or low ESR electrolytic capacitor. No matter
what type of bulk capacitor is used, an additional 0.1µF
ceramic capacitor placed directly adjacent to the INTVCC
and PGND pins is highly recommended. Good bypassing
is needed to supply the high transient currents required by
the MOSFET gate drivers and to prevent interaction between
the channels. The NPN linear regulator on the LTC3880-1
is not present and an external 5V supply is needed.
H
igh input voltage application in which large MOSFETs
are being driven at high frequencies may cause the maxi-
mum junction temperature rating for the LTC3880 to be
exceeded. The INTVCC current, of which a large percent-
age is due to the gate charge current, may be supplied by
either the internal 5V linear regulator or from an external
5V regulator on the LTC3880-1. If the LTC3880 is used
with the internal regulator activated, the power through
the IC is equal to VIN • IINTVCC. The gate charge current
is dependent on operating frequency as discussed in the
Efficiency Considerations section. The junction tempera-
ture can be estimated by using the equations in Note 2 of
the Electrical Characteristics. For example, the LTC3880
INTVCC current is limited to less than 69mA from a 24V
supply:
TJ = 70°C + 69mA • 24V • 33°C/W = 125°C
To prevent the maximum junction temperature from being
exceeded, a LTC3880-1 can be used. In the LTC3880-1,
the INTVCC linear regulator is disabled and approximately
2mA of current is supplied internally from VIN. Significant
system efficiency and thermal gains can be realized by
powering the EXTVCC pin from a switching 5V regulator.
The VIN current resulting from the gate driver and control
circuitry will be scaled by a factor of:
VEXTVCC
VIN
⎛
⎝
⎜
⎜
⎜
⎞
⎠
⎟
⎟
⎟
1
Efficiency
⎛
⎝
⎜
⎜
⎜
⎞
⎠
⎟
⎟
⎟
Tying the EXTVCC pin to a 5V supply (LTC3880-1 only)
reduces the junction temperature in the previous example
from 125°C to:
TJ = 70°C + 69mA • 5V • 33°C/W + 2mA • 24V • 33°C/W
= 83°C
Do not tie INTVCC on the LTC3880 to an external supply
because INTVCC will attempt to pull the external supply
high and hit current limit, significantly increasing the die
temperature.
For applications where VIN is 5V, tie the VIN and INTVCC
pins together and tie the combined pins to the 5V input
with a 1Ω or 2.2Ω resistor as shown in Figure 23. To mini-
mize the voltage drop caused by the gate charge current a
low ESR capacitor must be connected to the VIN/INTVCC
(EXTVCC) pins. This configuration will override the INTVCC
(EXTVCC) linear regulator and will prevent INTVCC (EXTVCC)
from dropping too low. Make sure the INTVCC (EXTVCC)
Figure 23. Setup for a 5V Input
RVIN
1Ω
CIN
3880 F23
5V
CINTVCC
4.7µF
+
INTVCC/EXTVCC
LTC3880
LTC3880-1
VIN
LTC3880/LTC3880-1
46
3880fg
For more information www.linear.com/LTC3880
APPLICATIONS INFORMATION
voltage exceeds the RDS(ON) test voltage for the MOSFETs
which is typically 4.5V for logic level devices. The UVLO
on INTVCC (EXTVCC) is set to approximately 4V. Both a
LTC3880 and LTC3880-1 are valid for this configuration.
TOPSIDE MOSFET DRIVER SUPPLY (CB, DB)
External bootstrap capacitors CB connected to the BOOST
pins supply the gate drive voltages for the topside MOSFETs.
Capacitor CB in the Block Diagram is charged though
external diode DB from INTVCC when the SW pin is low.
When one of the topside MOSFETs is to be turned on,
the driver places the CB voltage across the gate source
of the desired MOSFET. This enhances the MOSFET and
turns on the topside switch. The switch node voltage, SW,
rises to VIN and the BOOST pin follows. With the topside
MOSFET on, the boost voltage is above the input supply:
VBOOST = VIN + VINTVCC. The value of the boost capacitor
CB needs to be 100 times that of the total input capa-
citance of the topside MOSFET(s). The reverse break-
down of the external Schottky diode must be greater
than VIN(MAX). When adjusting the gate drive level, the
final arbiter is the total input current for the regulator. If
a change is made and the input current decreases, then
the efficiency has improved. If there is no change in input
current, then there is no change in efficiency.
PWM jitter has been observed in some designs operating
at higher VIN/VOUT ratios. This jitter does not substantially
affect the circuit accuracy. Referring to Figure 24, PWM
jitter can be removed by inserting a series resistor with a
value of 1Ω to 5Ω between the cathode of the diode and
the BOOSTn pin. A resistor case size of 0603 or larger is
recommended to reduce ESL and achieve the best results.
UNDERVOLTAGE LOCKOUT
The LTC3880 is initialized by an internal threshold-based
UVLO where VIN must be approximately 4V and INTVCC/
EXTVCC, VDD33, VDD25 must be within approximately 20%
of the regulated values. In addition, VDD33 must be within
approximately 7% of the targeted value before the RUN
and SHARE_CLK pins are released. After the part has
initialized, an additional comparator monitors VIN. The
VIN_ON threshold must be exceeded before the power
sequencing can begin. When VIN drops below the VIN_OFF
threshold, the SHARE_CLK pin will be pulled low and VIN
must increase above the VIN_ON threshold before the
controller will restart. The normal start-up sequence will
be allowed after the VIN_ON threshold is crossed.
It is possible to program the contents of the NVM in the
application if the VDD33 supply is externally driven. This will
activate the digital portion of the LTC3880 without engaging
the high voltage sections. PMBus communications are valid
in this supply configuration. If VIN has not been applied to
the LTC3880, bit 3 (NVM Not Initialized)in MFR_COMMON
will be asserted low. If this condition is detected, the part
will only respond to addresses 5A and 5B. To initialize
the part issue the following set of commands: global
address 0x5B command 0xBD data 0x2B followed by
global address 5B command 0xBD and data 0xC4. The
part will now respond to the correct address. Configure
the part as desired then issue a STORE_USER_ALL. When
VIN is applied a MFR_RESET command must be issued to
allow the PWM to be enabled and valid ADC conversions
to be read.
CIN AND COUT SELECTION
The selection of CIN is simplified by the 2-phase architec-
ture and its impact on the worst-case RMS current drawn
through the input network (battery/fuse/capacitor). It can
be shown that the worst-case capacitor RMS current oc-
curs when only one controller is operating. The controller
with the highest (VOUT)(IOUT) product needs to be used
in the formula below to determine the maximum RMS
capacitor current requirement. Increasing the output cur-
rent drawn from the other controller will actually decrease
the input RMS ripple current from its maximum value.
The out-of-phase technique typically reduces the input
Figure 24. Boost Circuit to Minimize PWM Jitter
VIN
TGATE
LTC3880
LTC3880-1
SW
INTVCC
BOOST
0.2µF
VIN
10µF
3880 F24
BGATE
PGND
LTC3880/LTC3880-1
47
3880fg
For more information www.linear.com/LTC3880
APPLICATIONS INFORMATION
capacitor’s RMS ripple current by a factor of 30% to 70%
when compared to a single phase power supply solution.
In continuous mode, the source current of the top MOSFET
is a square wave of duty cycle (VOUT)/(VIN). To prevent
large voltage transients, a low ESR capacitor sized for the
maximum RMS current of one channel must be used. The
maximum RMS capacitor current is given by:
CIN Required IRMS ≈IMAX
VIN
VOUT
( )
VIN – VOUT
( )
⎡
⎣
⎢⎤
⎦
⎥
1/2
This formula has a maximum at VIN = 2VOUT
, where
IRMS = IOUT/2. This simple worst-case condition is com-
monly used for design because even significant deviations
do not offer much relief. Note that capacitor manufacturers’
ripple current ratings are often based on only 2000 hours
of life. This makes it advisable to further derate the capaci-
tor, or to choose a capacitor rated at a higher temperature
than required. Several capacitors may be paralleled to meet
size or height requirements in the design. Due to the high
operating frequency of the LTC3880, ceramic capacitors
can also be used for CIN. Always consult the manufacturer
if there is any question.
The benefit of the LTC3880 2-phase operation can be
calculated by using the equation above for the higher
power controller and then calculating the loss that would
have resulted if both controller channels switched on at
the same time. The total RMS power lost is lower when
both controllers are operating due to the reduced overlap
of current pulses required through the input capacitor’s
ESR. This is why the input capacitor’s requirement cal-
culated above for the worst-case controller is adequate
for the dual controller design. Also, the input protection
fuse resistance, battery resistance, and PC board trace
resistance losses are also reduced due to the reduced
peak currents in a 2-phase system. The overall benefit of
a multiphase design will only be fully realized when the
source impedance of the power supply/battery is included
in the efficiency testing. The sources of the top MOSFETs
should be placed within 1cm of each other and share a
common CIN(s). Separating the sources and CIN may pro-
duce undesirable voltage and current resonances at VIN.
A small (0.1µF to 1µF) bypass capacitor between the chip
VIN pin and ground, placed close to the LTC3880, is also
suggested. A 2.2Ω – 10Ω resistor placed between CIN
(C1) and the VIN pin provides further isolation between
the two channels.
The selection of COUT is driven by the effective series
resistance (ESR). Typically, once the ESR requirement
is satisfied, the capacitance is adequate for filtering. The
output ripple (∆VOUT) is approximated by:
∆VOUT ≈IRIPPLE ESR +1
8fCOUT
⎛
⎝
⎜
⎜
⎜
⎞
⎠
⎟
⎟
⎟
where f is the operating frequency, COUT is the output
capacitance and IRIPPLE is the ripple current in the induc-
tor. The output ripple is highest at maximum input voltage
since IRIPPLE increases with input voltage.
FAULT CONDITIONS
The LTC3880 GPIOn pins are configurable to indicate a
variety of faults including OV/UV, OC, OT, timing faults,
peak overcurrent faults. In addition the GPIOn pins can
be pulled low by external sources indicating a fault in
some other portion of the system. The fault response is
configurable and allow the following options:
n Ignore
n Shut Down Immediately—Latch Off
n Shut Down Immediately—Retry Indefinitely at the Time
Interval Specified in MFR_RETRY_DELAY
Refer to the PMBus section of the data sheet and the
PMBus specification for more details.
The OV response is automatic and virtually immediate. If
an OV is detected, TG goes low and BG is asserted.
Fault logging is available on the LTC3880. The fault log-
ging is configurable to automatically store data when a
fault occurs that causes the unit to fault off. The header
portion of the fault logging table contains peak values. It
is possible to read these values at any time. This data will
be useful while troubleshooting the fault.
If the LTC3880 internal temperature is in excess of 85°C,
the write into the NVM is not recommended. The data will
still be held in RAM, unless the 3.3V supply UVLO thresh-
old is reached. If the die temperature exceeds 130°C all
LTC3880/LTC3880-1
48
3880fg
For more information www.linear.com/LTC3880
APPLICATIONS INFORMATION
NVM communication is disabled until the die temperature
drops below 120°C.
OPEN-DRAIN PINS
The LTC3880 has the following open-drain pins:
3.3V Pins
1. GPIOn
2. SYNC
3. SHARE_CLK
5V Pins (5V pins operate correctly when pulled to 3.3V.)
1. RUNn
2. ALERT
3. SCL
4. SDA
All the above pins have on-chip pull-down transistors
that can sink 3mA at 0.4V. The low threshold on the pins
is 1.4V; thus, plenty of margin on the digital signals with
3mA of current. For 3.3V pins, 3mA of current is a 1.1k
resistor. Unless there are transient speed issues associ-
ated with the RC time constant of the resistor pull-up and
parasitic capacitance to ground, a 10k resistor or larger
is generally recommended.
For high speed signals such as the SDA, SCL and SYNC,
a lower value resistor may be required. The RC time con-
stant should be set to 1/3 to 1/5 the required rise time
to avoid timing issues. For a 100pF load and a 400kHz
PMBus communication rate, the rise time must be less
than 300ns. The resistor pull-up on the SDA and SCL pins
with the time constant set to 1/3 the rise time:
RPULLUP =
t
RISE
3
•
100
pF =1k
The closest 1% resistor value is 1k. Be careful to minimize
parasitic capacitance on the SDA and SCL pins to avoid
communication problems. To estimate the loading
capacitance, monitor the signal in question and measure how
long it takes for the desired signal to reach approximately
63% of the output value. This is one time constant.
The SYNC pin has an on-chip pull-down transistor with the
output held low for nominally 500ns. If the internal oscil-
lator is set for 500kHz and the load is 100pF and a 3x time
constant is required, the resistor calculation is as follows:
RPULLUP =
2µs – 500ns
3 •100pF =5k
The closest 1% resistor is 4.99k.
If timing errors are occurring or if the SYNC frequency is
not as fast as desired, monitor the waveform and determine
if the RC time constant is too long for the application. If
possible reduce the parasitic capacitance. If not reduce
the pull up resistor sufficiently to assure proper timing.
The SHARE_CLK pull-up resistor has a similar equation
with a period of 10µs and a pull-down time of 1µs. The
RC time constant should be approximately 3µs or faster.
PHASE-LOCKED LOOP AND FREQUENCY
SYNCHRONIZATION
The LTC3880 has a phase-locked loop (PLL) comprised
of an internal voltage-controlled oscillator (VCO) and a
phase detector. The PLL is locked to the falling edge of
the SYNC pin. The phase relationship between channel 0,
channel 1 and the falling edge of SYNC is controlled by the
lower 3 bits of the MFR_PWM_CONFIG_LT C 3880 com-
mand. For PolyPhase applications, it is recommended all
the phases be spaced evenly. Thus for a 2-phase system
the signals should be 180° out of phase and a 4-phase
system should be spaced 90°.
The phase detector is an edge-sensitive digital type that
provides a known phase shift between the external and
internal oscillators. This type of phase detector does not
exhibit false lock to harmonics of the external clock.
The output of the phase detector is a pair of complemen-
tary current sources that charge or discharge the internal
filter network. The PLL lock range is guaranteed between
250kHz and 1MHz. Nominal parts will have a range beyond
this; however, operation to a wider frequency range is not
guaranteed.
LTC3880/LTC3880-1
49
3880fg
For more information www.linear.com/LTC3880
APPLICATIONS INFORMATION
The PLL has a lock detection circuit. If the PLL should lose
lock during operation, bit 4 of the STATUS_MFR_SPECIFIC
command is asserted and the ALERT pin is pulled low.
The fault can be cleared by writing a 1 to the bit. If the
user does not wish to see the PLL_FAULT, even if a
synchronization clock is not available at power up, bit 3
of the MFR_CONFIG_ALL_LTC3880 command must be
asserted.
If the SYNC signal is not clocking in the application, the
PLL will run at the lowest free running frequency of the
VCO. This will be well below the intended PWM frequency
of the application and may cause undesirable operation
of the converter.
If the PWM signal appears to be running at too high a
frequency, monitor the SYNC pin. Extra transitions on
the falling edge will result in the PLL trying to lock on to
noise versus the intended signal. Review routing of digital
control signals and minimize crosstalk to the SYNC signal
to avoid this problem. Multiple LTC3880s are required to
share the SYNC pin in PolyPhase configurations, for other
configurations it is optional. If the SYNC pin is shared be-
tween LTC3880s, only one LTC3880 can be programmed
with a frequency output. All the other LTC3880s must be
programmed to external clock.
MINIMUM ON-TIME CONSIDERATIONS
Minimum on-time, tON(MIN), is the smallest time duration
that the LTC3880 is capable of turning on the top MOSFET.
It is determined by internal timing delays and the gate
charge required to turn on the top MOSFET. Low duty
cycle applications may approach this minimum on-time
limit and care should be taken to ensure that:
tON(MIN) <
V
OUT
V
IN
• f
OSC
If the duty cycle falls below what can be accommodated
by the minimum on-time, the controller will begin to skip
cycles. The output voltage will continue to be regulated,
but the ripple voltage and current will increase.
The minimum on-time for the LTC3880 is approximately
90ns, with reasonably good PCB layout, minimum 30%
inductor current ripple and at least 10mV – 15mV ripple
on the current sense signal. The minimum on-time can be
affected by PCB switching noise in the voltage and cur-
rent loop. As the peak current sense voltage decreases,
the minimum on-time gradually increases to 130ns. This
is of particular concern in forced continuous applications
with low ripple current at light loads. If the duty cycle
drops below the minimum on-time limit in this situation,
a significant amount of cycle skipping can occur with cor-
respondingly larger current and voltage ripple.
RCONFIG (EXTERNAL RESISTOR
CONFIGURATION PINS)
The LTC3880 default NVM is programmed to respect the
RCONFIG pins. If a user wishes the output voltage, PWM
frequency and phasing and the address to be set without
programming the part or purchasing specially programmed
parts, the RCONFIG pins can be used to establish these
parameters. The RCONFIG pins all require a resistor di-
vider between the VDD25 and SGND of the LTC3880. The
RCONFIG pins are only monitored at initial power up and
during a reset so modifying their values perhaps using an
A/D after the part is powered will have no effect. 1% resis-
tors or better must be used to assure proper operation.
Noisy clock signals should not be routed near these pins.
Voltage Selection
When an output voltage is set using the RCONFIG pins on
VOUTn_CFG and VTRIMn_CFG, the following parameters
are set as a percentage of the output voltage:
• VOUT_OV_FAULT_LIMIT +10%
• VOUT_OV_WARN +7.5%
• VOUT_MAX +7.5%
• VOUT_MARGIN_HI +5%
• POWER_GOOD_ON –7%
• POWER_GOOD_OFF –8%
• VOUT_MARGIN_LO –5%
• VOUT_UV_WARN –6.5%
• VOUT_UV_FAULT_LIMIT –7%
LTC3880/LTC3880-1
50
3880fg
For more information www.linear.com/LTC3880
APPLICATIONS INFORMATION
Refer to Tables 12 and 13 to set the output voltage using
RCONFIG pins VOUTn_CFG and VTRIMn_CFG. RTOP is
connected between VDD25 and the pin and RBOTTOM is
connected between the pin and SGND. 1% resistors must
be used to assure proper operation.
The output voltage set point is equal to:
VSETPOINT = VOUTn_CFG + VTRIMn_CFG
For example, if the VOUTn_CFG pin has RTOP equal to
24.9k and RBOTTOM equal to 4.32k, and VTRIMn_CFG
is set with RTOP not inserted and RBOTTOM equal to 0Ω:
VSETPOINT = 1.1V – 0.099V or 1.001V
If odd values of output voltage are required from 0.5V
to 3.3V, use only the VOUTn_CFG resistor divider, the
VTRIM pin can be open or shorted to VDD25. If the output
set point is 5V, the VOUTn_CFG must have RTOP equal to
10k and RBOTTOM equal to 23.2k and VTRIMn_CFG must
have RTOP equal to 20k and RBOTTOM equal to 11k. If VOUT
is 2.5 volts or lower, low range is used. The maximum
voltage command on channel 0 is 4.096 volts including
VOUT_OV_FAULT, VOUT_OV_WARN, VOUT_MARGIN_HI
and VOUT.
Table 12. VOUTn_CFG
RTOP (kΩ) RBOTTOM (kΩ) VOUT (V)
0 or Open Open NVM
10 23.2 See VTRIM
10 15.8 3.3
16.2 20.5 3.1
16.2 17.4 2.9
20 17.8 2.7
20 15 2.5
20 12.7 2.3
20 11 2.1
24.9 11.3 1.9
24.9 9.09 1.7
24.9 7.32 1.5
24.9 5.76 1.3
24.9 4.32 1.1
30.1 3.57 0.9
30.1 1.96 0.7
Open 0 0.5
Table 13. VTRIMn_CFG
RTOP (kΩ) RBOTTOM (kΩ)
VTRIM (mV)
CHANGE TO
VSET VOLTAGE
VOUT (V)
IF VOUT HAS
10kΩ/23.3kΩ
0 or Open Open 0
10 23.2 99
10 15.8 86.625
16.2 20.5 74.25
16.2 17.4 61.875
20 17.8 49.5
20 15 37.125 5.5
20 12.7 24.75 5.25
20 11 12.375 5
24.9 11.3 –12.375 4.75
24.9 9.09 –24.75 4.5
24.9 7.32 –37.125 4.25
24.9 5.76 –49.5 4
24.9 4.32 –61.875 3.75
30.1 3.57 –74.25 3.63
30.1 1.96 –86.625 3.5
Open 0 –99 3.46
Frequency and Phase Selection Using RCONFIG
The frequency and phase commands are linked if they
are set using the RCONFIG pins. If PMBus commands
are used the two parameters are independent. The SYNC
pins must be shared in PolyPhase configurations where
multiple LTC3880s are used to produce the output. If
the configuration is not PolyPhase the SYNC pins do not
have to be shared. If the SYNC pins are shared between
LTC3880s only one SYNC pin can be set as a frequency
output, all other SYNC pins must be set to External Clock.
For example in a 4-phase configuration clocked at 425kHz,
one of the LTC3880s must be set to the desired frequency
and phase and the other LTC3880 must be set to External
Clock. All phasing is with respect to the falling edge of SYNC.
LTC3880/LTC3880-1
51
3880fg
For more information www.linear.com/LTC3880
APPLICATIONS INFORMATION
LTC3880 Chip 1 set the frequency to 425kHz with 90° and
270° phase shift:
RTOP = 20kΩ and RBOTTOM = 15kΩ
LTC3880 Chip 2 set the frequency to External Clock with
0° and 180° phase shift:
RTOP = open and RBOTTOM = 0Ω
Frequencies of 350kHz, 750kHz and 1000kHz can only be
set using NVM programming. If a 6-phase configuration
is desired, NVM programming will give optimal phasing.
All other configurations in frequency and phasing can be
achieved using the FREQ_CFG pin.
Address Selection Using RCONFIG
The LTC3880 address is selected using a combination of
the address stored in NVM and the ASEL pin. The MSB
of ASEL is the MSB in the NVM and the LSB is the ASEL
value. This allows 16 different LTC3880s on a single board
with one programmed address in NVM.
If the address stored in NVM is 0x4F, then the part address
can be set from 0x40 to 0x4F using ASEL. (The standard
default address is 0x4F). Do not set any part address to
0x5A or 0x5B because these are global addresses and all
parts will respond to them.
To choose address 0x40 RTOP is open and
RBOTTOM = 0Ω
To choose address 0x45 RTOP = 24.9k and
RBOTTOM = 7.32k
To choose address 0x4E RTOP = 10.0k and
RBOTTOM = 15.8k
Table 14. FREQ_CFG (Phase Based on Falling Edge of SYNC)
RTOP (kΩ) RBOTTOM (kΩ) FREQUENCY (kHz) θSYNC TO θ0θSYNC TO θ1DESCRIPTION
0 or Open Open NVM NVM NVM NVM
10 23.2 250 0 180 2-Phase
10 15.8 250 120 240 3-Phase
16.2 20.5 250 90 270 4-Phase
16.2 17.4 425 0 180 2-Phase
20 17.8 425 120 240 3-Phase
20 15 425 90 270 4-Phase
20 12.7 500 0 180 2-Phase
20 11 500 120 240 3-Phase
24.9 11.3 500 90 270 4-Phase
24.9 9.09 575 0 180 2-Phase
24.9 7.32 575 120 240 3-Phase
24.9 5.76 575 90 270 4-Phase
24.9 4.32 650 0 180 2-Phase
30.1 3.57 650 120 240 3-Phase
30.1 1.96 650 90 270 4-Phase
Open 0 External Clock 0 180 2-Phase
LTC3880/LTC3880-1
52
3880fg
For more information www.linear.com/LTC3880
APPLICATIONS INFORMATION
Table 15. ASEL
RTOP (kΩ) RBOTTOM (kΩ) SLAVE ADDRESS LSB HEX
0 or Open Open NVM
10 23.2 xyz_1111 F
10 15.8 xyz_1110 E
16.2 20.5 xyz_1101 D
16.2 17.4 xyz_1100 C
20 17.8 xyz_1011 B
20 15 xyz_1010 A
20 12.7 xyz_1001 9
20 11 xyz_1000 8
24.9 11.3 xyz_0111 7
24.9 9.09 xyz_0110 6
24.9 7.32 xyz_0101 5
24.9 5.76 xyz_0100 4
24.9 4.32 xyz_0011 3
30.1 3.57 xyz_0010 2
30.1 1.96 xyz_0001 1
Open 0 xyz_0000 0
EFFICIENCY CONSIDERATIONS
The percent efficiency of a switching regulator is equal to
the output power divided by the input power times 100%.
It is often useful to analyze individual losses to determine
what is limiting the efficiency and which change would
produce the most improvement. Percent efficiency can
be expressed as:
%Efficiency = 100% – (L1 + L2 + L3 + ...)
where L1, L2, etc. are the individual losses as a percent-
age of input power.
Although all dissipative elements in the circuit produce
losses, four main sources usually account for most of the
losses in LTC3880 circuits: 1) IC VIN current, 2) INTVCC
regulator current, 3) I2R losses, 4) Topside MOSFET
transition losses.
1. The VIN current is the DC supply current given in
the Electrical Characteristics table, which excludes
MOSFET driver and control currents. VIN current typi-
cally results in a small (<0.1%) loss.
2. INTVCC current is the sum of the MOSFET driver and
control currents. The MOSFET driver current results
from switching the gate capacitance of the power
MOSFETs. Each time a MOSFET gate is switched from
low to high to low again, a packet of charge dQ moves
from INTVCC to ground. The resulting dQ/dt is a cur-
rent out of INTVCC that is typically much larger than the
control circuit current. In continuous mode, IGATECHG
= f(QT + QB), where QT and QB are the gate charges of
the topside and bottom side MOSFETs.
On the LTC3880-1, supplying EXTVCC from an output-
derived source will scale the VIN current required for
the driver and control circuits by a factor of:
VEXTVCC
VIN
⎛
⎝
⎜
⎜
⎜
⎞
⎠
⎟
⎟
⎟
1
Efficiency
⎛
⎝
⎜
⎜
⎜
⎞
⎠
⎟
⎟
⎟
For example, in a 20V to 5V application, 10mA of INTVCC
current results in approximately 2.5mA of VIN current.
This reduces the mid-current loss from 10% or more
(if the driver was powered directly from VIN) to only a
few percent.
Table 15A1. LTC3880 MFR_ADDRESS Command Examples
Expressing Both 7- or 8-Bit Addressing
DESCRIPTION
HEX DEVICE
ADDRESS BIT
7
BIT
6
BIT
5
BIT
4
BIT
3
BIT
2
BIT
1
BIT
0 R/W7 BIT 8 BIT
Rail40x5A 0xB4 0 1 0 1 1 0 1 0 0
Global40x5B 0xB6 0 1 0 1 1 0 1 1 0
Default 0x4F 0x9E 0 1 0 0 1 1 1 1 0
Example 1 0x60 0xC0 0 1 1 0 0 0 0 0 0
Example 2 0x61 0xC2 0 1 1 0 0 0 0 1 0
Disabled2,3,5 10000000 0
Note 1: This table can be applied to the MFR_CHANNEL_ADDRESS,
and MFR_RAIL_ADDRESS commands as well as the MFR_ADDRESS
command.
Note 2: A disabled value in one command does not disable the device, nor
does it disable the Global address.
Note 3: A disabled value in one command does not inhibit the device from
responding to device addresses specified in other commands.
Note 4: It is not recommended to write the value 0x00, 0x0C (7 bit),
or 0x5A or 0x5B(7 bit) to the MFR_ADDRESS, MFR_CHANNEL_
ADDRESS or the MFR_RAIL_ADDRESS commands.
Note 5: To disable the address enter 0x80 in the MFR_ADDRESS
command. The 0x80 is greater than the 7-bit address field, disabling
the address.
LTC3880/LTC3880-1
53
3880fg
For more information www.linear.com/LTC3880
APPLICATIONS INFORMATION
3. I2R losses are predicted from the DC resistances of the
fuse (if used), MOSFET, inductor, current sense resistor.
In continuous mode, the average output current flows
through L and RSENSE, but is “chopped” between the
topside MOSFET and the synchronous MOSFET. If the
two MOSFETs have approximately the same RDS(ON),
then the resistance of one MOSFET can simply be
summed with the resistances of L and RSENSE to ob-
tain I2R losses. For example, if each RDS(ON) = 10mΩ,
RL = 10mΩ, RSENSE = 5mΩ, then the total resistance
is 25mΩ. This results in losses ranging from 2% to
8% as the output current increases from 3A to 15A for
a 5V output, or a 3% to 12% loss for a 3.3V output.
Efficiency varies as the inverse square of VOUT for the
same external components and output power level. The
combined effects of increasingly lower output voltages
and higher currents required by high performance digital
systems is not doubling but quadrupling the importance
of loss terms in the switching regulator system!
4. Transition losses apply only to the topside MOSFET(s),
and become significant only when operating at high
input voltages (typically 15V or greater). Transition
losses can be estimated from:
Transition Loss = (1.7) VIN2 IO(MAX) CRSS f
Other “hidden” losses such as copper trace and internal
battery resistances can account for an additional 5% to
10% efficiency degradation in portable systems. It is very
important to include these “system” level losses during
the design phase. The internal battery and fuse resistance
losses can be minimized by making sure that CIN has
adequate charge storage and very low ESR at the switch-
ing frequency. A 25W supply will typically require a
minimum of 20µF to 40µF of capacitance having
a maximum of 20mΩ to 50mΩ of ESR. The LTC3880
2-phase architecture typically halves this input capacitance
requirement over competing solutions. Other losses
including Schottky conduction losses during dead time
and inductor core losses generally account for less than
2% total additional loss.
CHECKING TRANSIENT RESPONSE
The regulator loop response can be checked by looking at
the load current transient response. Switching regulators
take several cycles to respond to a step in DC (resistive)
load current. When a load step occurs, VOUT shifts by an
amount equal to ∆ILOAD (ESR), where ESR is the effective
series resistance of COUT. ∆ILOAD also begins to charge or
discharge COUT generating the feedback error signal that
forces the regulator to adapt to the current change and
return VOUT to its steady-state value. During this recov-
ery time VOUT can be monitored for excessive overshoot
or ringing, which would indicate a stability problem.
The availability of the ITH pin not only allows optimization
of control loop behavior but also provides a DC-coupled
and AC-filtered closed-loop response test point. The DC
step, rise time and settling at this test point truly reflects
the closed loop response. Assuming a predominantly
second order system, phase margin and/or damping
factor can be estimated using the percentage of overshoot
seen at this pin. The bandwidth can also be estimated
by examining the rise time at the pin. The ITH external
components shown in the Typical Application circuit will
provide an adequate starting point for most applications.
The only two programmable parameters that affect loop
gain are the voltage range, bits 5 and 6 of the MFR_PWM_
CONFIG_LTC3880 command and the current range, bit 7
of the MFR_PWM_MODE_LTC3880 command. Be sure to
establish these settings prior to compensation calculation.
The ITH series RC-CC filter sets the dominant pole-zero
loop compensation. The values can be modified slightly
(from 0.5 to 2 times their suggested values) to optimize
transient response once the final PC layout is done and
the particular output capacitor type and value have been
determined. The output capacitors need to be selected
because the various types and values determine the
loop gain and phase. An output current pulse of 20%
to 80% of full-load current having a rise time of 1µs to
10µs will produce output voltage and ITH pin waveforms
that will give a sense of the overall loop stability without
LTC3880/LTC3880-1
54
3880fg
For more information www.linear.com/LTC3880
APPLICATIONS INFORMATION
breaking the feedback loop. Placing a power MOSFET with
a resistor to ground directly across the output capacitor
and driving the gate with an appropriate signal generator
is a practical way to produce to a load step. The MOSFET
+ RSERIES will produce output currents approximately
equal to VOUT/RSERIES. RSERIES values from 0.1Ω to 2Ω
are valid depending on the current limit settings and the
programmed output voltage. The initial output voltage
step resulting from the step change in output current may
not be within the bandwidth of the feedback loop, so this
signal cannot be used to determine phase margin. This
is why it is better to look at the ITH pin signal which is in
the feedback loop and is the filtered and compensated
control loop response. The gain of the loop will be in-
creased by increasing RC and the bandwidth of the loop
will be increased by decreasing CC. If RC is increased by
the same factor that CC is decreased, the zero frequency
will be kept the same, thereby keeping the phase shift the
same in the most critical frequency range of the feedback
loop. The output voltage settling behavior is related to the
stability of the closed-loop system and will demonstrate
the actual overall supply performance.
A second, more severe transient is caused by switching
in loads with large (>1µF) supply bypass capacitors. The
discharged bypass capacitors are effectively put in parallel
with COUT, causing a rapid drop in VOUT. No regulator can
alter its delivery of current quickly enough to prevent this
sudden step change in output voltage if the load switch
resistance is low and it is driven quickly. If the ratio of
CLOAD to COUT is greater than 1:50, the switch rise time
should be controlled so that the load rise time is limited
to approximately 25 • CLOAD. Thus a 10µF capacitor would
require a 250µs rise time, limiting the charging current
to about 200mA.
PC BOARD LAYOUT CHECKLIST
When laying out the printed circuit board, the following
checklist should be used to ensure proper operation of
the IC. These items are also illustrated graphically in the
layout diagram of Figure 25. Figure 26 illustrates the
current waveforms present in the various branches of
the 2-phase synchronous regulators operating in the
continuous mode. Check the following in your layout:
1. Are the top N-channel MOSFETs M1 and M2 located
within 1 cm of each other with a common drain con-
nection at CIN? Do not attempt to split the input de-
coupling for the two channels as it can cause a large
resonant loop.
2. Are the signal and power grounds kept separate? The
combined IC signal ground pin and the ground return of
CINTVCC must return to the combined COUT (–) terminals.
The ITH traces should be as short as possible. The path
formed by the top N-channel MOSFET, Schottky diode
and the CIN capacitor should have short leads and PC
trace lengths. The output capacitor (–) terminals should
be connected as close as possible to the (–) terminals
of the input capacitor by placing the capacitors next to
each other and away from the Schottky loop described
above.
3. Does the LTC3880 VSENSE lines equal VOUT? VOUT0 is
differential. VOUT1 should reference the SGND (Pin 41)
to the Load 1 ground.
4. Are the ISENSE+ and ISENSE– leads routed together with
minimum PC trace spacing? The filter capacitor between
ISENSE+ and ISENSE– should be as close as possible to
the IC. Ensure accurate current sensing with Kelvin
connections at the sense resistor or inductor, whichever
is used for current sensing.
LTC3880/LTC3880-1
55
3880fg
For more information www.linear.com/LTC3880
APPLICATIONS INFORMATION
Figure 25. Recommended Printed Circuit Layout Diagram
Figure 26. Branch Current Waveforms
CB0
CB1
CINTVCC
+
CIN
D1
1µF
CERAMIC
M1 M2
M3 M4 D2
+
CVIN
VIN
RIN
L1
L0
COUT1
VOUT1
GND
VOUT0
3880 F25
+
COUT2
+
RSENSE0
RSENSE1
fIN
1µF
CERAMIC
ITH1
VSENSE1
ISENSE1+
ISENSE1–
ISENSE0–
ISENSE0+
VSENSE0+
ITH0
TG1
SW1
BOOST1
BG1
VIN
PGND
INTVCC
BG0
BOOST0
SW0
TG0
SGND
SYNC
RUN0
RUN1
LTC3880
VSENSE0–
RL1
D1
L1
SW1 RSENSE1 VOUT1
COUT1
VIN
CIN
RIN
RL0
D0
BOLD LINES INDICATE
HIGH SWITCHING
CURRENT. KEEP LINES
TO A MINIMUM LENGTH.
L0
SW0
3880 F26
RSENSE0 VOUT0
COUT0
LTC3880/LTC3880-1
56
3880fg
For more information www.linear.com/LTC3880
5. Is the INTVCC decoupling capacitor connected close
to the IC, between the INTVCC and the power ground
pins? This capacitor carries the MOSFET drivers current
peaks. An additional 1µF ceramic capacitor placed im-
mediately next to the INTVCC and PGND pins can help
improve noise performance substantially.
6. Keep the switching nodes (SW1, SW0), top gate nodes
(TG1, TG0), and boost nodes (BOOST1, BOOST0) away
from sensitive small-signal nodes, especially from the
opposite channel’s voltage and current sensing feed-
back pins. All of these nodes have very large and fast
moving signals and therefore should be kept on the
“output side” of the LTC3880 and occupy minimum
PC trace area. If DCR sensing is used, place the top
resistor (Figure 18a, R1) close to the switching node.
7. Use a modified “star ground” technique: a low imped-
ance, large copper area central grounding point on
the same side of the PC board as the input and output
capacitors with tie-ins for the bottom of the INTVCC
decoupling capacitor, the bottom of the voltage feedback
resistive divider and the SGND pin of the IC.
PC BOARD LAYOUT DEBUGGING
Start with one controller at a time. It is helpful to use a
DC-50MHz current probe to monitor the current in the
inductor while testing the circuit. Monitor the output
switching node (SW pin) to synchronize the oscilloscope
to the internal oscillator and probe the actual output voltage
as well. Check for proper performance over the operating
voltage and current range expected in the application.
The frequency of operation should be maintained over
the input voltage range down to dropout and until the
output load drops below the low current operation
threshold—typically 10% of the maximum designed cur-
rent level in Burst Mode operation.
The duty cycle percentage should be maintained from
cycle to cycle in a well-designed, low noise PCB imple-
mentation. Variation in the duty cycle at a subharmonic
rate can suggest noise pickup at the current or voltage
sensing inputs or inadequate loop compensation. Over-
compensation of the loop can be used to tame a poor PC
layout if regulator bandwidth optimization is not required.
Only after each controller is checked for its individual
performance should both controllers be turned on at the
same time. A particularly difficult region of operation is
when one controller channel is nearing its current com-
parator trip point when the other channel is turning on
its top MOSFET. This occurs around 50% duty cycle on
either channel due to the phasing of the internal clocks
and may cause minor duty cycle jitter.
Reduce VIN from its nominal level to verify operation of
the regulator in dropout. Check the operation of the un-
dervoltage lockout circuit by further lowering VIN while
monitoring the outputs to verify operation.
Investigate whether any problems exist only at higher out-
put currents or only at higher input voltages. If problems
coincide with high input voltages and low output currents,
look for capacitive coupling between the BOOST, SW, TG,
and possibly BG connections and the sensitive voltage
and current pins. The capacitor placed across the current
sensing pins needs to be placed immediately adjacent to
the pins of the IC. This capacitor helps to minimize the
effects of differential noise injection due to high frequency
capacitive coupling. If problems are encountered with
high current output loading at lower input voltages, look
for inductive coupling between CIN, Schottky and the top
MOSFET components to the sensitive current and voltage
sensing traces. In addition, investigate common ground
path voltage pickup between these components and the
SGND pin of the IC.
APPLICATIONS INFORMATION
LTC3880/LTC3880-1
57
3880fg
For more information www.linear.com/LTC3880
APPLICATIONS INFORMATION
DESIGN EXAMPLE
As a design example for a two channel medium current
regulator, assume VIN = 12V nominal, VIN = 20V maximum,
VOUT0 = 3.3V, VOUT1 = 1.8V, IMAX0,1 = 15A and f = 500kHz
(see Figure 27).
The regulated output is established by the VOUT_
COMMAND stored in NVM or placing the following resis-
tor divider between VDD25 the RCONFIG pin and SGND:
1. VOUT0_CFG, RTOP = 10k, RBOTTOM = 15.8k
2. VTRIM0_CFG, Open
3. VOUT1_CFG, RTOP = 24.9k, RBOTTOM = 11.3k
4. VTRIM1_CFG, RTOP = Open, RBOTTOM = 0Ω
The frequency and phase are set by NVM or by setting
the resistor divider between VDD25 FREQ_CFG and SGND
with RTOP = 20k and RBOTTOM = 12.7k. The address is set
to XF where X is the MSB stored in NVM.
VIN
VDD33 VDD25
SGND
TG0
0.1µF
4.99k
0.1µF
1µF
1µF
L0, L1: VISHAY IHLP-4040DZ-11 1µH, 0.56µH
M1, M2: INFINEON BSC050N03LS
M3, M4: INFINEON BSC010NE2LSI
1µF
4700pF
0.22µF 0.22µF
2200pF
22µF
V
IN
6V TO 24V
10µF
+
530µF
D2
M2
M4
10k
15.8k
VDD25
M1
M3
V
OUT1
1.8V
15A
4.99k 4.99k
2.0k
1µF
L1
0.56µH
L0
1.0µH
D1
TG1
BG0
SYNC
10k
24.9k
11.3k
10k
1µF
1.58k
23.2k
20k
12.7k
GPIO0
10k
GPIO1
10k
SDA
10k
SCL
10k
ALERT
10k
RUN0
FREQ_CFG
VOUT0_CFG
VOUT1_CFG
VTRIM0_CFG
VTRIM1_CFG
ASEL
10k
RUN1
WP
10k
2.0k 1.58k
SHARE_CLK
VDD33
BG1
PGND
BOOST0 BOOST1
SW0 SW1
INTVCC
LTC3880
TSNS0 TSNS1
ITHO ITH1
ISENSEO+ISENSE1+
VSENSEO+VSENSE1
VSENSEO–
ISENSEO–ISENSE1–
V
OUT0
3.3V
15A
VOUT1
1.8V
15A
VOUT1
1.8V
15A
+
530µF
3880 F27
220pF 220pF10nF 10nF
Figure 27. High Efficiency Dual 500kHz 3.3V/1.8V Step-Down Converter
LTC3880/LTC3880-1
58
3880fg
For more information www.linear.com/LTC3880
APPLICATIONS INFORMATION
The following parameters are set as a percentage of the
output voltage if the resistor configuration pins are used
to determined output voltage:
n VOUT_OV_FAULT_LIMIT .................................... +10%
n VOUT_OV_WARN .............................................. +7.5%
n VOUT_MAX....................................................... +7.5%
n VOUT_MARGIN_HI ..............................................+5%
n POWER_GOOD_ON .............................................–7%
n POWER_GOOD_OFF ............................................–8%
n VOUT_MARGIN_LO .............................................–5%
n VOUT_UV_WARN ..............................................–6.5%
n VOUT_UV_FAULT_LIMIT ......................................–7%
All other user defined parameters must be programmed
into the NVM. The GUI can be utilized to quickly set up
the part with the desired operating parameters.
The inductance values are based on a 35% maximum
ripple current assumption (5.25A for each channel). The
highest value of ripple current occurs at the maximum
input voltage:
L=VOUT
f • ∆IL(MAX)
1– VOUT
VIN(MAX)
⎡
⎣
⎢
⎢
⎢
⎤
⎦
⎥
⎥
⎥
Channel 0 will require 1.05µH and channel 1 will require
0.624µH. The nearest standard values are 1µH and 0.68µH
respectively. At the nominal input the ripple will be:
∆IL(NOM) =VOUT
f •L 1– VOUT
VIN(NOM)
⎡
⎣
⎢
⎢
⎢
⎤
⎦
⎥
⎥
⎥
Channel 0 will have 4.79A (32%) ripple, and channel 1 will
have 5.5A (30%) ripple. The peak inductor current will be
the maximum DC value plus one-half the ripple current
or 17.39A for channel 0 and 17.75A for channel 1. The
minimum on time occurs on channel 1 at the maximum
VIN, and should not be less than 90ns:
tON(MIN) =VOUT
VIN(MAX) • f =1.8V
20V 500kHz
( )
=180ns
The Vishay IHLP4040DZ-11 1µH (2.3mΩ DCRTYP at 25°C)
channel 0 and the VishayIHLP4040DZ-11 0.56µH (1.61mΩ
DCRTYP at 25°C) channel 1 are chosen.
Assuming the temperature measurement of the inductor
temperature is accurate and C1 is set to 0.2µF, RD is infinite
and removed from the equations.
R0 =
L
DCR at 25°C
( )
• C1 =
1µH
2.3mΩ• 0.22µF =2k
The maximum power loss in R0 is related to the duty
cycle, and will occur in continuous mode at the maximum
input voltage:
PLOSSR0 =VIN(MAX) – VOUT
( )
• VOUT
R1
=20 – 3.3
( )
• 3.3
2k
=27.55mW
The respective values for channel 1 are R1 = 2k, R2 is
open and PLOSSR1 = 20.73mW.
The current limit will be set 20% higher than the peak
value to assure variation in components and noise in the
system do not limit the average current.
VILIMIT = IPEAK • RDCR(MAX) = 17.39A • 2.5mΩ = 43mV
The closest VILIMIT setting is 42.9mV or 46.4mV. The values
are entered with the IOUT_OC_FAULT_LIMIT command.
Based on expected variation and measurement in the lab
across the sense capacitor the user can determine the
optimal setting. For channel 1 the VILIMT value is 28.6mV.
The closest value is 28.6mV.
The power dissipation on the top side MOSFET can be
easily estimated. Choose a RENESAS RJK0305DPB topside
MOSFET. RDS(ON) = 10mΩ, CMILLER = 75pF. At maximum
input voltage with T estimated = 50°C and a bottom side
MOSFET a RENESAS RJK0330DPB, RDS(ON) = 3mΩ:
P
MAIN =3.3V
20V • 17.39
( )
2• 1+0.005
( )
50°C – 25°C
( )
⎡
⎣
⎢⎤
⎦
⎥
• 0.006Ω+ 20V
( )
28.695A
( )
•1
5 – 2.3 +1
2.3
⎛
⎝
⎜
⎜
⎞
⎠
⎟
⎟
75pF
( )
500kHz
( )
=0.386W
LTC3880/LTC3880-1
59
3880fg
For more information www.linear.com/LTC3880
The loss in the bottom side MOSFET is:
PSYNC =20V – 3.3V
( )
20V • 17.39A
( )
2•
1+0.005
( )
50°C – 25°C
( )
⎡
⎣
⎢⎤
⎦
⎥• 0.001
Ω
=0.312W
Both MOSFETS have I2R losses while the PMAIN equation
includes an additional term for transition losses, which
are highest at high input voltages.
CIN is chosen for an RMS current rating of:
CIN Required IRMS =
17.39
20 3.3
( )
• 20 – 3.3
( )
⎡
⎣
⎢⎤
⎦
⎥1/2
=6.5A
at temperature assuming only channel 0 or 1 is on. COUT
is chosen with an ESR of 0.006Ω for low output ripple.
The output ripple in continuous mode will be highest at
the maximum input voltage. The output voltage ripple
due to ESR is
VORIPPLE = R(∆IL) = 0.006Ω • 5.5A = 33mV.
APPLICATIONS INFORMATION
VIN
V
IN
VDD33 VDD25
SDA
1µF
1µF
VGS MAX ON THE TP0101K IS 8V IF VIN > 16V
CHANGE THE RESISTOR DIVIDER ON THE PFET GATE
1µF
1µF
3880 F28
10k
100k
TP0101K
ISOLATED 3.3V
SDA
SCL
TP0101K
100k
LTC
CONTROLLER
HEADER
TO LTC DC1613
USB TO I
2C/SMBus/PMBus
CONTROLLER
SCL
WP SGND
LTC3880
VIN
VDD33
SDA
SCL
WP SGND
LTC3880
10k
VDD25
Figure 28. LT C Controller Connection
CONNECTING THE USB TO THE I2C/SMBus/PMBus
CONTROLLER TO THE LTC3880 IN SYSTEM
The LTC USB to I2C/SMBus/PMBus controller can be
interfaced to the LTC3880 on the user’s board for pro-
gramming, telemetry and system debug. The controller,
when used in conjunction with LTpowerPlay, provides a
powerful way to debug an entire power system. Faults are
quickly diagnosed using telemetry, fault status registers
and the fault log. The final configuration can be quickly
developed and stored to the LTC3880 EEPROM.
Figure 28 illustrates the application schematic for
powering, programming and communication with one
or more LTC3880s via the LTC I2C/SMBus/PMBus
controller regardless of whether or not system power is
present. If system power is not present the dongle will
power the LTC3880 through the VDD33 supply pin. To
initialize the part when VIN is not applied and the VDD33
pin is powered use global address 5B command 0xBD
data 0x2B followed by address 5B command 0xBD data
0xC4. The part can now be communicated with, and the
project file updated. To write the updated project file to the
NVM issue a STORE_USER_ALL command. When VIN is
LTC3880/LTC3880-1
60
3880fg
For more information www.linear.com/LTC3880
APPLICATIONS INFORMATION
applied, a MFR_RESET must be issued to allow the PWM
to be enabled and valid ADCs to be read.
Because of the controllers limited current sourcing capabil-
ity, only the LTC3880s, their associated pull-up resistors
and the I2C pull-up resistors should be powered from the
ORed 3.3V supply. In addition any device sharing the I2C
bus connections with the LTC3880 should not have body
diodes between the SDA/SCL pins and their respective
VDD node because this will interfere with bus communica-
tion in the absence of system power. If VIN is applied the
dongle will not supply the LTC3880s on the board. It is
recommended the RUN pins be held low to avoid providing
power to the load until the part is fully configured.
The LTC controller I2C connections are optoisolated from
the PC USB. The 3.3V from the controller and the LTC3880
VDD33 pin must be driven to each LTC3880 with a separate
PFET. If VIN is not applied, the VDD33 pins can be in parallel
because the on-chip LDO is off. The controller 3.3V cur-
rent limit is 100mA but typical VDD33 currents are under
15mA. The VDD33 does back drive the INTVCC/EXTVCC pin.
Normally this is not an issue if VIN is open.
LTpowerPlay: AN INTERACTIVE GUI FOR DIGITAL
POWER
LTpowerPlay is a powerful Windows-based development
environment that supports Linear Technology digital
power ICs including the LTC3880. The software supports
a variety of different tasks. LTpowerPlay can be used to
evaluate Linear Technology ICs by connecting to a demo
board or the user application. LTpowerPlay can also be
used in an offline mode (with no hardware present) in
order to build multiple IC configuration files that can be
Figure 29
LTC3880/LTC3880-1
61
3880fg
For more information www.linear.com/LTC3880
APPLICATIONS INFORMATION
saved and re-loaded at a later time. LTpowerPlay provides
unprecedented diagnostic and debug features. It becomes
a valuable diagnostic tool during board bring-up to pro-
gram or tweak the power system or to diagnose power
issues when bring up rails. LTpowerPlay utilizes Linear
Technology’s USB-to-I2C/SMBus/PMBus controller to
communication with one of the many potential targets
including the DC1590B-A/B demo board, the DC1709A
socketed programming board, or a customer target
system. The software also provides an automatic update
feature to keep the revisions current with the latest set of
device drivers and documentation. A great deal of context
sensitive help is available with LTpowerPlay along with
several tutorial demos. Complete information is available at
http://www.linear.com/ltpowerplay.
PMBus COMMUNICATION AND COMMAND
PROCESSING
The LTC3880/LTC3880-1 have a one deep buffer to hold
the last data written for each supported command prior
to processing as shown in Figure 30; Write Command
Data Processing. When the part receives a new command
from the bus, it copies the data into the Write Command
Data Buffer, indicates to the internal processor that this
command data needs to be fetched, and converts the
command to its internal format so that it can be executed.
Tw o distinct parallel blocks manage command buffering
and command processing (fetch, convert, and execute)
to ensure the last data written to any command is never
lost. Command data buffering handles incoming PMBus
writes by storing the command data to the Write Com-
mand Data Buffer and marking these commands for future
processing. The internal processor runs in parallel and
handles the sometimes slower task of fetching, convert-
ing and executing commands marked for processing.
Some computationally intensive commands (e.g., timing
parameters, temperatures, voltages and currents) have
internal processor execution times that may be long relative
to PMBus timing. If the part is busy processing a command,
and new command(s) arrive, execution may be delayed
or processed in a different order than received. The part
indicates when internal calculations are in process via bit5
of MFR_COMMON (‘calculations not pending’). When the
part is busy calculating, bit 5 is cleared. When this bit is
set, the part is ready for another command. An example
polling loop is provided in Figure 30 which ensures that
commands are processed in order while simplifying error
handling routines.
When the part receives a new command while it is busy,
it will communicate this condition using standard PMBus
protocol. Depending on part configuration it may either
NACK the command or return all ones (0xFF) for reads. It
may also generate a BUSY fault and ALERT notification,
or stretch the SCL clock low. For more information refer
to PMBus Specification v1.1, Part II, Section 10.8.7 and
SMBus v2.0 section 4.3.3. Clock stretching can be enabled
by asserting bit 1 of MFR_CONFIG_ALL_LTC3880. Clock
stretching will only occur if enabled and the bus com-
munication speed exceeds 100kHz.
PMBus busy protocols are well accepted standards, but
can make writing system level software somewhat com-
plex. The part provides three ‘hand shaking’ status bits
which reduce complexity while enabling robust system
level communication.
The three hand shaking status bits are in the MFR_
COMMON register. When the part is busy executing an
internal operation, it will clear bit 6 of MFR_COMMON
(‘chip not busy’). When the part is busy specifically
because it is in a transitional VOUT state (margining hi/lo,
power off/on, moving to a new output voltage set point,
etc.) it will clear bit 4 of MFR_COMMON (‘output not in
transition’). When internal calculations are in process, the
part will clear bit5 of MFR_COMMON (‘calculations not
pending’). These three status bits can be polled with a
PMBus read byte of the MFR_COMMON register until all
DECODER
CMD
INTERNAL
PROCESSOR
WRITE COMMAND
DATA BUFFER
PAGE
CMDS
0x00
0x21
0xFD
3880 F30
x1
•
•
•
•
•
•
MFR_RESET
VOUT_COMMAND
S
CALCULATIONS
PENDING
PMBus
WRITE
R
FETCH,
CONVERT
DATA
AND
EXECUTE
DATA
MUX
Figure 30. Write Command Data Processing
LTC3880/LTC3880-1
62
3880fg
For more information www.linear.com/LTC3880
Figure 31. Example of a Command Write of VOUT_COMMAND
// wait until bits 6, 5, and 4 of MFR_COMMON are all set
do
{
mfrCommonValue = PMBUS_READ_BYTE(0xEF);
partReady = (mfrCommonValue & 0x68) == 0x68;
}
while(!partReady)
// n
ow the part is ready to receive the next command
PMBUS_WRITE_WORD(0x21, 0x2000); //write VOUT_COMMAND to 2V
APPLICATIONS INFORMATION
three bits are set. A command immediately following the
status bits being set will be accepted without NACKing or
generating a BUSY fault/ALERT notification. The part can
NACK commands for other reasons, however, as required
by the PMBus spec (for instance, an invalid command or
data). An example of a robust command write algorithm
for the VOUT_COMMAND register is provided in Figure 31.
WORD() subroutine. The above polling mechanism allows
your software to remain clean and simple while robustly
communicating with the part. For a detailed discussion
of these topics and other special cases please refer to
the application note section located at www.linear.com/
designtools/app_notes.
When communicating using bus speeds at or below
100kHz, the polling mechanism shown here provides a
simple solution that ensures robust communication without
clock stretching. At bus speeds in excess of 100kHz, it is
strongly recommended that the part be configured to en-
able clock stretching. This requires a PMBus master that
supports clock stretching. System software that detects
and properly recovers from the standard PMBus NACK/
BUSY faults as described in the PMBus Specification v1.1,
Part II, Section 10.8.7 is required to communicate above
100kHz without clock stretching.
It is recommended that all command writes (write byte,
write word, etc.) be preceded with a polling loop to avoid
the extra complexity of dealing with busy behavior and
unwanted ALERTB notification. A simple way to achieve
this is to create a SAFE_WRITE_BYTE() and SAFE_WRITE_
LTC3880/LTC3880-1
63
3880fg
For more information www.linear.com/LTC3880
PMBus
COMMAND DETAILS
ADDRESSING AND WRITE PROTECT
COMMAND NAME
CMD
CODE DESCRIPTION TYPE PAGED
DATA
FORMAT UNITS NVM
DEFAULT
VALUE
PAGE 0x00 Channel or page currently selected for any
command that supports paging.
R/W Byte N Reg 0x00
WRITE_PROTECT 0x10 Level of protection provided by the device
against accidental changes.
R/W Byte N Reg Y 0x00
MFR_ADDRESS 0xE6 Sets the 7-bit I2C address byte. R/W Byte N Reg Y 0x4F
MFR_CHANNEL_ADDRESS 0xD8 Address to the PAGE activated channel R/W Byte Y Reg Y 0x80
MFR_RAIL_ADDRESS 0xFA Common address for PolyPhase outputs to
adjust common parameters.
R/W Byte Y Reg Y 0x80
PAGE
The page command provides the ability to configure, control and monitor both outputs through only one physical ad-
dress. Each PAGE contains the Operating Memory for each output.
Pages 0x00 and 0x01 correspond to channel 0 and channel 1, respectively, in this device.
Setting the page to 0xFF means that the commands are to applied to both outputs. Performing READ commands with
PAGE set to 0xFF will return the same value as PAGE 0. When PAGE is set to 0xFF there are no restrictions on R/W
commands.
This command has one data byte.
WRITE_PROTECT
The WRITE_PROTECT command is used to control writing to the LTC3880 device. This command does not indicate
the status of the WP pin which is defined in the MFR_COMMON command. The WP pin takes precedence over the
value of this command unless the WRITE_PROTECT command is more stringent.
BYTE MEANING
0x80 Disable all writes except to the WRITE_PROTECT, PAGE_MFR_
EE_UNLOCK and STORE_USER_ALL command
0x40 Disable all writes except to the WRITE_PROTECT, PAGE,
MFR_EE_UNLOCK, MFR_CLEAR_PEAKS, STORE_USER_ALL,
OPERATION and CLEAR_FAULTS command. ndividual fault
bits can be cleared by writing a 1 to the respective bits in the
STATUS registers.
0x20 Disable all writes except to the WRITE_PROTECT, OPERATION,
MFR_EE_UNLOCK, MFR_CLEAR_PEAKS, CLEAR_FAULTS,
PAGE, ON_OFF_CONFIG, VOUT_COMMAND and STORE_USER_
ALL. Individual fault bits can be cleared by writing a 1 to the
respective bits in the STATUS registers.
0x10 Reserved, must be 0
0x08 Reserved, must be 0
0x04 Reserved, must be 0
0x02 Reserved, must be 0
0x01 Reserved, must be 0
Enable writes to all commands when WRITE_PROTECT is set to 0x00.
This command has one data byte.
LTC3880/LTC3880-1
64
3880fg
For more information www.linear.com/LTC3880
If WP pin is high, PAGE, OPERATION, MFR_CLEAR_PEAKS, MFR_EE_UNLOCK and CLEAR_FAULTS commands are
supported. Individual fault bits can be cleared by writing a 1 to the respective bits in the STATUS registers.
MFR_ADDRESS
The MFR_ADDRESS command byte sets the 7 bits of the PMBus slave address for this device.
Setting this command to a value of 0x80 disables device addressing. The GLOBAL device address, 0x5A and 0x5B,
cannot be deactivated. If RCONFIG is set to ignore, the ASEL pin is still used to determine the LSB of the channel ad-
dress. If the ASEL pin is open, the LTC3880 will use the address value stored in NVM.
This command has one data byte.
MFR_CHANNEL_ADDRESS
The MFR_CHANNEL_ADDRESS command enables direct device address access to the PAGE activated channel. The
value of this command should be unique on the PMBus and should not be the same as another channel or device.
If this command is not set to 0x80, a status condition specific to this channel will result in the Alert Response Address
(ARA) value to be equal to the value of the MFR_CHANNEL_ADDRESS command.
Setting this command to a value of 0x80 disables channel device addressing for the channel.
This command has one data byte.
MFR_RAIL_ADDRESS
The MFR_RAIL_ADDRESS command enables direct device address access to the PAGE activated channel. The value
of this command should be common to all devices attached to a single power supply rail.
The user should only perform command writes to this address. If a read is performed from this address and the rail
devices do not respond with EXACTLY the same value, the LTC3880 will detect bus contention and set a CML com-
munications fault.
Setting this command to a value of 0x80 disables rail device addressing for the channel.
This command has one data byte.
PMBus
COMMAND DETAILS
LTC3880/LTC3880-1
65
3880fg
For more information www.linear.com/LTC3880
GENERAL CONFIGURATION REGISTERS
COMMAND NAME CMD CODE DESCRIPTION TYPE PAGED
DATA
FORMAT UNITS NVM
DEFAULT
VALUE
MFR_CHAN_CONFIG_LTC 3880 0xD0 Configuration bits that are channel specific. R/W Byte Y Reg Y 0x1F
MFR_CONFIG_ALL_LTC 3880 0xD1 Configuration bits that are common to all
pages.
R/W Byte N Reg Y 0x09
MFR_CHAN_CONFIG_LTC3880
General purpose configuration command common to multiple LTC products.
BIT MEANING
7 Reserved
6 Reserved
5 Reserved
4 Disable RUN Low. When asserted the RUN pin is not pulsed low if commanded OFF
3 Short Cycle. When asserted the output will immediate off if commanded ON while waiting for TOFF_DELAY or TOFF_FALL. TOFF_MIN of 120mS
is honored then the part will command ON.
2 SHARE_CLOCK control, if SHARE_CLOCK is held low, the output is disabled
1 No GPIO ALERT, ALERT is not pulled low if GPIO is pulled low externally. Assert this bit if either POWER_GOOD or VOUT_UVUF (PGOOD) is
propagated on GPIO
0 Disables the VOUT decay value requirement for MFR_RETRY_TIME processing. When this bit is set to a 0, the output must decay to less than
12.5% of the programmed value for any action that turns off the rail including a fault, an OFF/ON command, or a toggle of RUN from high to low
to high.
This command has one data byte.
MFR_CONFIG_ALL_LTC3880
General purpose configuration command common to multiple LTC products
BIT MEANING
7 Enable Fault Logging
6 Ignore Resistor Configuration Pins
5 Reserved, set to 1
4 Reserved
3 Mask PLL Unlock Fault
2 PMBus command writes require a valid Packet Error Checking, PEC, byte to be accepted.*
1 Enable the use of PMBus clock stretching
0 Enables a low to high transition on either RUN pin to issue a CLEAR_FAULTS command
*PMBus command writes that have a valid PEC byte are always processed. PMBus command
writes that have an invalid PEC byte are not processed and set a CML status fault.
This command has one data byte.
PMBus
COMMAND DETAILS
LTC3880/LTC3880-1
66
3880fg
For more information www.linear.com/LTC3880
ON/OFF/MARGIN
COMMAND NAME
CMD
CODE DESCRIPTION TYPE PAGED
DATA
FORMAT UNITS NVM
DEFAULT
VALUE
ON_OFF_CONFIG 0x02 RUN pin and PMBus bus on/off command configuration. R/W Byte Y Reg Y 0x1E
OPERATION 0x01 Operating mode control. On/off, margin high and margin
low.
R/W Byte Y Reg Y 0x80
MFR_RESET 0xFD Commanded reset without requiring a power-down. Send Byte N NA
ON_OFF_CONFIG
The ON_OFF_CONFIG command configures the combination of RUNn pin input and serial bus commands needed to
turn the unit on and off. This includes how the unit responds when power is applied.
Table 3. Supported Values:
VALUE MEANING
0x1F OPERATION value and RUNn pin must both command the device to start/run. Device executes immediate off when commanded off.
0x1E OPERATION value and RUNn pin must both command the device to start/run. Device uses TOFF_command values when commanded off.
0x17 RUNn pin control with immediate off when commanded off. OPERATION on/off control ignored.
0x19 RUNn pin control using TOFF_command values when commanded off. OPERATION on/off control ignored.
Note: A high on the RUN pin is always required to start power conversion. Power conversion will always stop with a low on RUN.
Programming an unsupported ON_OFF_CONFIG value will generate a CML fault and the command will be ignored.
This command has one data byte.
PMBus
COMMAND DETAILS
LTC3880/LTC3880-1
67
3880fg
For more information www.linear.com/LTC3880
OPERATION
The OPERATION command is used to turn the unit on and off in conjunction with the input from the RUNn pins. It
is also used to cause the unit to set the output voltage to the upper or lower MARGIN VOLTAGEs. The unit stays in
the commanded operating mode until a subsequent OPERATION command or change in the state of the RUNn pin
instructs the device to change to another mode. If the part is stored in the MARGIN_LOW/HIGH state, the next RESET
or POWER_ON cycle will ramp to that state. If the OPERATION command is modified, for example ON is changed to
MARGIN_LOW, the output will move at a fixed slope set by the VOUT_TRANSITION_RATE.
Margin High (Ignore Faults) and Margin Low (Ignore Faults) operations are not supported by the LTC3880.
The part defaults to the ON state.
This command has one data byte.
Table 4. OPERATION Command Detail Register OPERATION Data Contents
When On_Off_Config_Use_PMBus Enables Operation_Control
SYMBOL Action Value
BITS
FUNCTION
Turn off immediately 0x00
Turn on 0x80
Margin Low 0x98
Margin High 0xA8
Sequence off 0x40
OPERATION Data Contents When On_Off_Config is Configured Such That
OPERATION Command Is Not Used to Command Channel On or Off
SYMBOL Action Value
BITS
FUNCTION
Output at Nominal 0x80
Margin Low 0x98
Margin High 0xA8
Note: Attempts to write a reserved value will cause a CML fault.
MFR_RESET
This command provides a means by which the user can perform a reset of the LTC3880.
This write-only command has no data bytes.
PMBus
COMMAND DETAILS
LTC3880/LTC3880-1
68
3880fg
For more information www.linear.com/LTC3880
PWM CONFIG
COMMAND NAME CMD CODE DESCRIPTION TYPE PAGED
DATA
FORMAT UNITS NVM
DEFAULT
VALUE
MFR_PWM_MODE_
LTC 3880
0xD4 Configuration for the PWM engine of each channel R/W Byte Y Reg Y 0xC2
MFR_PWM_CONFIG_
LTC 3880
0xF5 Set numerous parameters for the DC/DC controller
including phasing.
R/W Byte N Reg Y 0x10
FREQUENCY_SWITCH 0x33 Switching frequency of the controller R/W Word N L11 kHz Y 350
0xFABC
MFR_PWM_MODE_LTC3880
The MFR_PWM_MODE_LT C 3880 command allows the user to program the PWM controller to use Burst Mode operation,
discontinuous (pulse-skipping mode), or forced continuous conduction mode.
BIT MEANING
7 Use High Range of ILIMIT
0 – Low Current Range
1 – High Current Range
6 Enable Servo Mode
5 Reserved
4 Reserved
3 Reserved
2 Reserved
Bit[1:0] Mode
00b Discontinuous
01b Burst Mode Operation
10b Forced Continuous
Whenever the channel is ramping on, the PWM mode will be discontinuous, regardless of the value of this
command.
Bit [7] of this command determines if the part is in high range or low range of the IOUT_OC_FAULT_LIMIT command.
Changing this bit value changes the PWM loop gain and compensation. Changing this bit value whenever an output is
active may have detrimental system results.
Bit [6] The LTC3880 will not servo while the part is OFF, ramping on or ramping off. When set to a one, the output servo
is enabled. The output set point DAC will be slowly adjusted to minimize the difference between the READ_VOUT_ADC
and the VOUT_COMMAND (or the appropriate margined value).
This command has one data byte.
MFR_PWM_CONFIG_LTC3880
The MFR_PWM_CONFIG_LTC3880 command sets the switching frequency phase offset with respect to the falling edge
of the SYNC signal. The part must be in the OFF state to process this command. Either the RUN pins must be low or
the part must be commanded off. If the part is in the RUN state and this command is written, the command will be
ignored and a BUSY fault will be asserted. Bits 5 and 6 of this command affect the loop gain of the respective channels
which may require modifications to the external compensation network.
PMBus
COMMAND DETAILS
LTC3880/LTC3880-1
69
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PMBus
COMMAND DETAILS
BIT MEANING
7 Reserved, set to 0.
6 If VOUT0 RANGE = 1, the maximum output voltage
for V0 is 2.75V. If RANGE = 0, the maximum
output voltage for V0 is 4.096V.
5 If VOUT1 RANGE = 1, the maximum output voltage
for V1 is 2.75V. If RANGE = 0, the maximum
output voltage for V1 is 5.5V.
4 Share Clock Enable : If this bit is 1, the
SHARE_CLK pin will not be released until
VIN > VIN_ON. The SHARE_CLK pin will be
pulled low when VIN < VIN_OFF. If this bit is 0, the
SHARE_CLK pin will not be pulled low when VIN <
VIN_OFF except for the initial application of VIN.
3 Reserved
BIT [2:0] CHANNEL 0 (DEGREES) CHANNEL 1 (DEGREES)
000b 0 180
001b 90 270
010b 0 240
011b 0 120
100b 120 240
101b 60 240
110b 120 300
This command has one data byte.
FREQUENCY_SWITCH
The FREQUENCY_SWITCH command sets the switching frequency, in kHz, of a PMBus device.
Supported Frequencies:
VALUE [15:0] RESULTING FREQUENCY (TYP)
0x0000 External Oscillator
0xF3E8 250kHz
0xFABC 350kHz
0xFB52 425kHz
0xFBE8 500kHz
0x023F 575kHz
0x028A 650kHz
0x02EE 750kHz
0x03E8 1000kHz
The part must be in the OFF state to process this command. Either the RUN pins must be low or the part must be
commanded off. If the part is in the RUN state and this command is written, the command will be ignored and a BUSY
fault will be asserted. When the part is commanded off and the frequency is changed, a PLL_UNLOCK status may be
detected as the PLL locks onto the new frequency.
This command has two data bytes and is formatted in Linear_5s_11s format.
LTC3880/LTC3880-1
70
3880fg
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VOLTAGE
Input Voltage and Limits
COMMAND NAME CMD CODE DESCRIPTION TYPE PAGED
DATA
FORMAT UNITS NVM
DEFAULT
VALUE
VIN_OV_FAULT_ LIMIT 0x55 Input supply overvoltage fault limit. R/W Word N L11 V Y 15.5
0xD3E0
VIN_UV_WARN_LIMIT 0x58 Input supply undervoltage warning limit. R/W Word N L11 V Y 6.3
0xCB26
VIN_ON 0x35 Input voltage at which the unit should start power
conversion.
R/W Word N L11 V Y 6.5
0xCB40
VIN_OFF 0x36 Input voltage at which the unit should stop power
conversion.
R/W Word N L11 V Y 6.0
0xCB00
VIN_OV_FAULT_LIMIT
The VIN_OV_FAULT_LIMIT command sets the value of the measured input voltage, in volts, that causes an input
overvoltage fault. The fault is detected with the A/D converter resulting in latency up to 90ms.
This command has two data bytes and is formatted in Linear_5s_11s format.
VIN_UV_WARN_LIMIT
The VIN_UV_WARN_LIMIT command sets the value of the input voltage that causes an input undervoltage warning.
The warning is detected with the A/D converter resulting in latency up to 90ms.
This command has two data bytes and is formatted in Linear_5s_11s format.
VIN_ON
The VIN_ON command sets the input voltage, in volts, at which the unit should start power conversion.
This command has two data bytes and is formatted in Linear_5s_11s format.
VIN_OFF
The VIN_OFF command sets the input voltage, in volts, at which the unit should stop power conversion.
This command has two data bytes and is formatted in Linear_5s_11s format.
PMBus
COMMAND DETAILS
LTC3880/LTC3880-1
71
3880fg
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PMBus
COMMAND DETAILS
Output Voltage and Limits
COMMAND NAME CMD CODE DESCRIPTION TYPE PAGED
DATA
FORMAT UNITS NVM
DEFAULT
VALUE
VOUT_MODE 0x20 Output voltage format and exponent (2–12). R Byte Y Reg 2–2
0x14
VOUT_MAX 0x24 Upper limit on the commanded output voltage
including VOUT_MARGIN_HIGH.
R/W Word Y L16 V Y 4.096 Ch0
0x4189
5.5 Ch1
0x5800
VOUT_OV_FAULT_ LIMIT 0x40 Output overvoltage fault limit. R/W Word Y L16 V Y 1.1
0x119A
VOUT_OV_WARN_ LIMIT 0x42 Output overvoltage warning limit. R/W Word Y L16 V Y 1.075
0x1133
VOUT_MARGIN_HIGH 0x25 Margin high output voltage set point. Must be
greater than VOUT_COMMAND.
R/W Word Y L16 V Y 1.05
0x10CD
VOUT_COMMAND 0x21 Nominal output voltage set point. R/W Word Y L16 V Y 1.0
0x1000
VOUT_MARGIN_LOW 0x26 Margin low output voltage set point. Must be
less than VOUT_COMMAND.
R/W Word Y L16 V Y 0.95
0x0F33
VOUT_UV_WARN_ LIMIT 0x43 Output undervoltage warning limit. R/W Word Y L16 V Y 0.925
0x0ECD
VOUT_UV_FAULT_ LIMIT 0x44 Output undervoltage fault limit. R/W Word Y L16 V Y 0.9
0x0E66
POWER_GOOD_ON 0x5E Output voltage at or above which a power
good should be asserted.
R/W Word Y L16 V Y 0.93
0x0EE1
POWER_GOOD_OFF 0x5F Output voltage at or below which a power
good should be de-asserted.
R/W Word Y L16 V Y 0.92
0x0EB8
MFR_VOUT_MAX 0xA5 Maximum allowed voltage command
including VOUT_OV_FAULT_LIMIT.
R Word Y L16 V 4.096 Ch0
5.5 Ch1
VOUT_MODE
The data byte for VOUT_MODE command, used for commanding and reading output voltage, consists of a 3-bit mode
(only linear format is supported) and a 5-bit parameter representing the exponent used in output voltage Read/Write
commands.
This read-only command has one data byte
VOUT_MAX
The VOUT_MAX command sets an upper limit on the output voltage, including VOUT_MARGIN_HIGH, the unit can
command regardless of any other commands or combinations.
This command has two data bytes and is formatted in Linear_16u format.
VOUT_OV_FAULT_LIMIT
The VOUT_OV_FAULT_LIMIT command sets the value of the output voltage measured at the sense pins, in volts, which
causes an output overvoltage fault.
If the VOUT_OV_FAULT_LIMIT is modified and the switcher is active, allow 10ms after the command is modified to
assure the new value is being honored. The part indicates if it is busy making a calculation. Monitor bits 5 and 6 of
LTC3880/LTC3880-1
72
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PMBus
COMMAND DETAILS
MFR_COMMON. Either bit is low if the part is busy. If this wait time is not met, and the VOUT_COMMAND is modified
above the old overvoltage limit, an OV condition might temporarily be detected resulting in undesirable behavior and
possible damage to the switcher.
If VOUT_OV_FAULT_RESPONSE is set to OV_PULLDOWN, the GPIO pin will not assert if VOUT_OV_FAULT is propa-
gated. The LTC3880 will pull the TG low and assert the BG bit as soon as the overvoltage condition is detected.
This command has two data bytes and is formatted in Linear_16u format.
VOUT_OV_WARN_LIMIT
The VOUT_OV_WARN_LIMIT command sets the value of the output voltage measured at the sense pins, in volts, which
causes an output voltage high warning. The READ_VOUT value will be used to determine if this limit has been exceeded.
In response to the VOUT_OV_WARN_LIMIT being exceeded, the device:
• Sets the NONE_OF_THE_ABOVE bit in the STATUS_BYTE
• Sets the VOUT bit in the STATUS_WORD
• Sets the VOUT Overvoltage Warning bit in the STATUS_VOUT command
• Notifies the host by asserting ALERT pin
This condition is detected by the ADC so the response time may be up to 90ms.
This command has two data bytes and is formatted in Linear_16u format.
VOUT_MARGIN_HIGH
The VOUT_MARGIN_HIGH command loads the unit with the voltage to which the output is to be changed, in volts,
when the OPERATION command is set to “Margin High”. The value must be greater than VOUT_COMMAND.
This command will not be acted on during TON_RISE and TOFF_FALL output sequencing. The VOUT_TRANSITION_RATE
will be used if this command is modified while the output is active and in a steady-state condition.
This command has two data bytes and is formatted in Linear_16u format.
VOUT_COMMAND
The VOUT_COMMAND consists of two bytes and is used to set the output voltage, in volts.
This command will not be acted on during TON_RISE and TOFF_FALL output sequencing. The VOUT_TRANSITION_RATE
will be used if this command is modified while the output is active and in a steady-state condition.
This command has two data bytes and is formatted in Linear_16u format.
VOUT_MARGIN_LOW
The VOUT_MARGIN_LOW command loads the unit with the voltage to which the output is to be changed, in volts,
when the OPERATION command is set to “Margin Low”. The value must be less than VOUT_COMMAND.
This command will not be acted on during TON_RISE and TOFF_FALL output sequencing. The VOUT_TRANSITION_RATE
will be used if this command is modified while the output is active and in a steady-state condition.
This command has two data bytes and is formatted in Linear_16u format.
LTC3880/LTC3880-1
73
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For more information www.linear.com/LTC3880
PMBus
COMMAND DETAILS
VOUT_UV_WARN_LIMIT
The VOUT_UV_ WARN_LIMIT command reads the value of the output voltage measured at the sense pins, in volts,
which causes an output voltage low warning.
In response to the VOUT_UV_WARN_LIMIT being exceeded, the device:
• Sets the NONE_OF_THE_ABOVE bit in the STATUS_BYTE
• Sets the VOUT bit in the STATUS_WORD
• Sets the VOUT Undervoltage Warning bit in the STATUS_VOUT command
• Notifies the host by asserting ALERT pin
This condition is detected by the ADC so the response time may be up to 90ms.
This command has two data bytes and is formatted in Linear_16u format.
VOUT_UV_FAULT_LIMIT
The VOUT_UV_FAULT_LIMIT command reads the value of the output voltage measured at the sense pins, in volts,
which causes an output undervoltage fault.
This command has two data bytes and is formatted in Linear_16u format.
POWER_GOOD_ON
The POWER_GOOD_ON command sets the output voltage at which the POWER_GOOD signal should be asserted.
POWER_GOOD_ON is detected with an A/D read resulting in latency of up to 90ms.
This command has two data bytes and is formatted in Linear_16u format.
POWER_GOOD_OFF
The POWER_GOOD_OFF command sets the output voltage at which the POWER_GOOD signal should be negated.
POWER_GOOD_OFF is detected with an A/D read resulting in latency of up to 90ms. At initial power up the output of
this pin will be high even though the state should be low. If the proper state at power-up is required, place a Schottky
diode between RUN and GPIO. The Anode must be tied to GPIO and the Cathode to RUN.
The POWER_GOOD_ON status is masked from initiating an ALERT. The POWER_GOOD status bit in the STATUS_WORD
command is always reflective of VOUT wrt. the POWER_GOOD threshold.
This command has two data bytes and is formatted in Linear_16u format.
MFR_VOUT_MAX
The MFR_VOUT_MAX command is the maximum output voltage in volts for each channel including VOUT_OV_
FAULT_LIMIT. If the output voltages are set to high range (Bits 5 and 6 of MFR_PWM_CONFIG_LTC3880 set to a 0)
MFR_VOUT_MAX for channel 0 is 4.096V and MFR_VOUT_MAX for channel 1 is 5.5V. If the output voltages are set
to low range (Bits 5 and 6 of MFR_PWM_CONFIG_LTC3880 set to a 1) the MFR_VOUT_MAX for both channels is
2.75V. Entering VOUT_COMMAND values greater than this will result in a CML fault and the output voltage setting will
be clamped to the maximum level.
This read-only command has 2 data bytes and is formatted in Linear_16u format.
LTC3880/LTC3880-1
74
3880fg
For more information www.linear.com/LTC3880
PMBus
COMMAND DETAILS
CURRENT
Input Current Calibration
COMMAND NAME CMD CODE DESCRIPTION TYPE PAGED
DATA
FORMAT UNITS NVM
DEFAULT
VALUE
MFR_IIN_OFFSET 0xE9 Coefficient used to add to the input current to
account for the IQ of the part.
R/W
Word
Y L11 A Y 0.050
0x9333
MFR_IIN_OFFSET
The MFR_IIN_OFFSET command allows the user to set an input current representing the quiescent current of each
channel. For accurate results at low output current, the part should be in continuous conduction mode.
This command has 2 data bytes and is formatted in Linear_5s_11s format.
Output Current Calibration
COMMAND NAME
CMD
CODE DESCRIPTION TYPE PAGED
DATA
FORMAT UNITS NVM
DEFAULT
VALUE
IOUT_CAL_GAIN 0x38 The ratio of the voltage at the current sense pins
to the sensed current. For devices using a fixed
current sense resistor, it is the resistance value
in mΩ.
R/W Word Y L11 mΩ Y 1.8
0xBB9A
MFR_IOUT_CAL_GAIN_TC 0xF6 Temperature coefficient of the current sensing
element.
R/W Word Y CF Y 3900
0x0F3C
IOUT_CAL_GAIN
The IOUT_CAL_GAIN command is used to set the resistance value of the current sense resistor in milliohms. (see
also MFR_IOUT_CAL_GAIN_TC).
This command has two data bytes and is formatted in Linear_5s_11s format.
MFR_IOUT_CAL_GAIN_TC
The MFR_IOUT_CAL_GAIN_TC command allows the user to program the temperature coefficient of the IOUT_CAL_GAIN
sense resistor or inductor DCR in ppm/°C.
This command has two data bytes and is formatted in 16-bit 2’s complement integer ppm. N = –32768 to 32767 •
10–6. Nominal temperature is 27°C. The IOUT_CAL_GAIN is multiplied by:
[1.0 + MFR_IOUT_CAL_GAIN_TC • (READ_TEMPERATURE_1-27)]. DCR sensing will have a typical value of 3900.
The IOUT_CAL_GAIN and MFR_IOUT_CAL_GAIN_TC impact all current parameters including: READ_IOUT, READ_IIN,
IOUT_OC_FAULT_LIMIT and IOUT_OC_WARN_LIMIT.
Input Current
COMMAND NAME CMD CODE DESCRIPTION TYPE PAGED
DATA
FORMAT UNITS NVM
DEFAULT
VALUE
IIN_OC_WARN_LIMIT 0x5D Input overcurrent warning limit. R/W Word N L11 A Y 10.0
0xD280
LTC3880/LTC3880-1
75
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PMBus
COMMAND DETAILS
IIN_OC_WARN_LIMIT
The IIN_OC_WARN_LIMIT command sets the value of the input current, in amperes, that causes a warning indicating
the input current is high. The READ_IIN value will be used to determine if this limit has been exceeded.
In response to the IIN_OC_WARN_LIMIT being exceeded, the device:
• Sets the OTHER bit in the STATUS_BYTE
• Sets the INPUT bit in the upper byte of the STATUS_WORD
• Sets the IIN Overcurrent Warning bit in the STATUS_INPUT command, and
• Notifies the host by asserting ALERT pin
This condition is detected by the ADC so the response time may be up to 90ms.
This command has two data bytes and is formatted in Linear_5s_11s format.
Output Current
COMMAND NAME CMD CODE DESCRIPTION TYPE PAGED
DATA
FORMAT UNITS NVM
DEFAULT
VALUE
IOUT_OC_FAULT_LIMIT 0x46 Output overcurrent fault limit. R/W Word Y L11 A Y 29.75
0xDBB8
IOUT_OC_WARN_LIMIT 0x4A Output overcurrent warning limit. R/W Word Y L11 A Y 20.0
0xDA80
IOUT_OC_FAULT_LIMIT
The IOUT_OC_FAULT_LIMIT command sets the value of the peak output current limit, in amperes. When the controller
is in current limit, the overcurrent detector will indicate an overcurrent fault condition. The programmed overcurrent
fault limit value is rounded up to the nearest one of the following set of discrete values:
25mV/IOUT_CAL_GAIN Low Range (1.5x Nominal Loop Gain)
MFR_PWM_MODE_LTC 3880 [7]=0
28.6mV/IOUT_CAL_GAIN
32.1mV/IOUT_CAL_GAIN
35.7mV/IOUT_CAL_GAIN
39.3mV/IOUT_CAL_GAIN
42.9mV/IOUT_CAL_GAIN
46.4mV/IOUT_CAL_GAIN
50mV/IOUT_CAL_GAIN
37.5mV/IOUT_CAL_GAIN High Range (Nominal Loop Gain)
MFR_PWM_MODE_LTC 3880 [7]=1
42.9mV/IOUT_CAL_GAIN
48.2mV/IOUT_CAL_GAIN
53.6mV/IOUT_CAL_GAIN
58.9mV/IOUT_CAL_GAIN
64.3mV/IOUT_CAL_GAIN
69.6mV/IOUT_CAL_GAIN
75mV/IOUT_CAL_GAIN
Note: This is the peak of the current waveform. The READ_IOUT command returns the average current. The peak output
LTC3880/LTC3880-1
76
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PMBus
COMMAND DETAILS
current limits are adjusted with temperature based on the MFR_IOUT_CAL_GAIN_TC using the equation:
IOUT_OC_FAULT_LIMIT = IOUT_CAL_GAIN • (1 + MFR_IOUT_CAL_GAIN_TC • (READ_TEMPERTURE_1-27.0)).
The LTpowerPlay GUI automatically convert the voltages to currents.
The IOUT range is set with bit 7 of the MFR_PWM_MODE_LTC3880 command.
The IOUT_OC_FAULT_LIMIT is ignored during TON_RISE and TOFF_FALL.
This command has two data bytes and is formatted in Linear_5s_11s format.
IOUT_OC_WARN_LIMIT
This command sets the value of the output current that causes an output overcurrent warning in amperes. The
READ_IOUT value will be used to determine if this limit has been exceeded.
In response to the IOUT_OC_WARN_LIMIT being exceeded, the device:
• Sets the NONE_OF_THE_ABOVE bit in the STATUS_BYTE
• Sets the IOUT bit in the STATUS_WORD
• Sets the IOUT Overcurrent Warning bit in the STATUS_IOUT command, and
• Notifies the host by asserting ALERT pin
This condition is detected by the ADC so the response time may be up to 90ms.
The IOUT_OC_FAULT_LIMIT is ignored during TON_RISE and TOFF_FALL.
This command has two data bytes and is formatted in Linear_5s_11s format
TEMPERATURE
External Temperature Calibration
COMMAND NAME CMD CODE DESCRIPTION TYPE PAGED
DATA
FORMAT UNITS NVM
DEFAULT
VALUE
MFR_TEMP_1_GAIN 0xF8 Sets the slope of the external temperature
sensor.
R/W Word Y CF Y 1
0x4000
MFR_TEMP_1_OFFSET 0xF9 Sets the offset of the external temperature
sensor with respect to –273.1°C.
R/W Word Y L11 C Y 0
0x8000
MFR_TEMP_1_GAIN
The MFR_TEMP_1_GAIN command will modify the slope of the external temperature sensor to account for non-idealities
in the element and errors associated with the remote sensing of the temperature in the inductor.
This command has two data bytes and is formatted in 16-bit 2’s complement integer. N = 8192 to 32767. The effective
adjustment is N • 2–14. The nominal value is 1.
MFR_TEMP_1_OFFSET
The MFR_TEMP_1_OFFSET command will modify the offset of the external temperature sensor to account for non-
idealities in the element and errors associated with the remote sensing of the temperature in the inductor.
LTC3880/LTC3880-1
77
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PMBus
COMMAND DETAILS
This command has two data bytes and is formatted in Linear_5s_11s format. The part starts the calculation with a
value of –273.15 so the default adjustment value is zero.
External Temperature Limits
COMMAND NAME CMD CODE DESCRIPTION TYPE PAGED
DATA
FORMAT UNITS NVM
DEFAULT
VALUE
OT_FAULT_LIMIT 0x4F External overtemperature fault limit. R/W Word Y L11 C Y 100.0
0xEB20
OT_WARN_LIMIT 0x51 External overtemperature warning limit. R/W Word Y L11 C Y 85.0
0xEAA8
UT_FAULT_LIMIT 0x53 External undertemperature fault limit. R/W Word Y L11 C Y –40.0
0xE580
OT_FAULT_LIMIT
The OT_FAULT_LIMIT command sets the value of the external sense temperature, in degrees Celsius, which causes an
overtemperature fault. The READ_TEMPERATURE_1 value will be used to determine if this limit has been exceeded.
This condition is detected by the ADC so the response time may be up to 90ms.
This command has two data bytes and is formatted in Linear_5s_11s format.
OT_WARN_LIMIT
The OT_WARN_LIMIT command sets the value of the external sense temperature, in degrees Celsius, which causes an
overtemperature warning. The READ_TEMPERATURE_1 value will be used to determine if this limit has been exceeded.
In response to the OT_WARN_LIMIT being exceeded, the device:
• Sets the TEMPERATURE bit in the STATUS_BYTE
• Sets the Overtemperature Warning bit in the STATUS_TEMPERATURE command, and
• Notifies the host by asserting ALERT pin.
This condition is detected by the ADC so the response time may be up to 90ms.
This command has two data bytes and is formatted in Linear_5s_11s format.
UT_FAULT_LIMIT
The UT_FAULT_LIMIT command sets the value of the external sense temperature, in degrees Celsius, which causes
an undertemperature fault. The READ_TEMPERATURE_1 value will be used to determine if this limit has been
exceeded.
Note: If the temp sensors are not installed, the UT_FAULT_LIMIT can be set to –275°C and UT_FAULT_LIMIT response
set to ignore to avoid ALERT being asserted.
This condition is detected by the ADC so the response time may be up to 90ms.
Values of greater than 0.1V/ms and less than or equal to 1V/ms are recommended. If a transition rate out of this range
is desired, contact the factory for more information.
This command has two data bytes and is formatted in Linear_5s_11s format.
LTC3880/LTC3880-1
78
3880fg
For more information www.linear.com/LTC3880
PMBus
COMMAND DETAILS
TIMING
Timing—On Sequence/Ramp
COMMAND NAME CMD CODE DESCRIPTION
TYPE PAGED
DATA
FORMAT UNITS NVM
DEFAULT
VALUE
TON_DELAY 0x60 Time from RUN and/or Operation on to output
rail turn-on.
R/W Word Y L11 ms Y 0.0
0x8000
TON_RISE 0x61 Time from when the output starts to rise
until the output voltage reaches the VOUT
commanded value.
R/W Word Y L11 ms Y 8.0
0xD200
TON_MAX_FAULT_LIMIT 0x62 Maximum time from VOUT_EN on for VOUT to
cross the VOUT_UV_FAULT_LIMIT.
R/W Word Y L11 ms Y 10.0
0xD280
VOUT_TRANSITION_RATE 0x27 Rate the output changes when VOUT
commanded to a new value.
R/W Word Y L11 V/ms Y 0.25
0xAA00
TON_DELAY
The TON_DELAY command sets the time, in milliseconds, from when a start condition is received until the output
voltage starts to rise. Values from 0ms to 83 seconds are valid.
This command has two data bytes and is formatted in Linear_5s_11s format.
TON_RISE
The TON_RISE command sets the time, in milliseconds, from the time the output starts to rise to the time the output
enters the regulation band. Values from 0 to 1.3 seconds are valid. The part will be in discontinuous mode during
TON_RISE events. If TON_RISE is less than 0.25ms, the LTC3880 digital slope will be bypassed. The output voltage
transition will be controlled by the analog performance of the PWM switcher. The maximum allowed slope is 4V/ms.
This command has two data bytes and is formatted in Linear_5s_11s format.
TON_MAX_FAULT_LIMIT
The TON_MAX_FAULT_LIMIT command sets the value, in milliseconds, on how long the unit can attempt to power
up the output without reaching the output undervoltage fault limit.
A data value of 0ms means that there is no limit and that the unit can attempt to bring up the output voltage indefinitely.
The maximum limit is 83 seconds.
This command has two data bytes and is formatted in Linear_5s_11s format.
VOUT_TRANSITION_RATE
When a PMBus device receives either a VOUT_COMMAND or OPERATION (Margin High, Margin Low) that causes the
output voltage to change this command set the rate in V/ms at which the output voltage changes. This commanded
rate of change does not apply when the unit is commanded on or off.
Values of greater than 0.1V/ms are recommended.
This command has two data bytes and is formatted in Linear_5s_11s format.
LTC3880/LTC3880-1
79
3880fg
For more information www.linear.com/LTC3880
PMBus
COMMAND DETAILS
Timing—Off Sequence/Ramp
COMMAND NAME CMD CODE DESCRIPTION TYPE PAGED
DATA
FORMAT UNITS NVM
DEFAULT
VALUE
TOFF_DELAY 0x64 Time from RUN and/or Operation off to the start
of TOFF_FALL ramp.
R/W Word Y L11 ms Y 0.0
0x8000
TOFF_FALL 0x65 Time from when the output starts to fall until the
output reaches zero volts.
R/W Word Y L11 ms Y 8.0
0xD200
TOFF_MAX_WARN_LIMIT 0x66 Maximum allowed time, after TOFF_FALL
completed, for the unit to decay below 12.5%.
R/W Word Y L11 ms Y 150
0xF258
TOFF_DELAY
The TOFF_DELAY command sets the time, in milliseconds, from when a stop condition is received until the output
voltage starts to fall. Values from 0 to 83 seconds are valid.
This command is excluded from fault events.
This command has two data bytes and is formatted in Linear_5s_11s format.
TOFF_FALL
The TOFF_FALL command sets the time, in milliseconds, from the end of the turn-off delay time until the output volt-
age is commanded to zero. It is the ramp time of the VOUT DAC. When the VOUT DAC is zero, the part will three-state.
The part will maintain the mode of operation programmed. For defined TOFF_FALL times, the user should set the part
to continuous conduction mode. Loading the max value indicates the part will ramp down at the slowest possible rate.
The minimum supported fall time is 0.25ms. A value less than 0.25ms will result in a 0.25ms ramp. The maximum fall
time is 1.3 seconds. The maximum allowed slope is 4V/ms.
In discontinuous conduction mode, the controller will not draw current from the load and the fall time will be set by
the output capacitance and load current.
This command has two data bytes and is formatted in Linear_5s_11s format.
TOFF_MAX_WARN_LIMIT
The TOFF_MAX_WARN_LIMIT command sets the value, in milliseconds, on how long the unit can attempt to turn off
the output until a warning is asserted. The output is considered off when the VOUT voltage is less than 12.5% of the
programmed VOUT_COMMAND value. The calculation begins after TOFF_FALL is complete. TOFF_MAX_WARN is not
enabled in VOUT_DECAY is disabled.
A data value of 0ms means that there is no limit and that the unit can attempt to turn off the output voltage indefinitely.
Other than 0, values from 120ms to 524 seconds are valid.
This command has two data bytes and is formatted in Linear_5s_11s format.
Precondition for Restart
COMMAND NAME CMD CODE DESCRIPTION TYPE PAGED
DATA
FORMAT UNITS NVM
DEFAULT
VALUE
MFR_RESTART_ DELAY 0xDC Delay from actual RUN active edge to virtual
RUN active edge.
R/W Word Y L11 ms Y 500
0xFBE8
LTC3880/LTC3880-1
80
3880fg
For more information www.linear.com/LTC3880
PMBus
COMMAND DETAILS
MFR_RESTART_DELAY
This command specifies the minimum RUN off time in milliseconds. This device will pull the RUN pin low for this length
of time once a falling edge of RUN has been detected. The minimum recommended value is 136ms.
Note: The restart delay is different than the retry delay. The restart delay pulls run low for the specified time, after which
a standard start-up sequence is initiated. The minimum restart delay should be equal to TOFF_DELAY + TOFF_FALL
+ 136ms. Valid values are from 136ms to 65.52 seconds in 16ms increments. To assure a minimum off time, set
the MFR_RESTART_DELAY 16ms longer than the desired time. The output rail can be off longer than the MFR_
RESTART_DELAY after the RUN pin is pulled high if the output decay bit 1 is enabled in MFR_CHAN_CONFIG_LTC3880
and the output takes a long time to decay below 12.5% of the programmed value.
This command has two data bytes and is formatted in Linear_5s_11s format.
FAULT RESPONSE
Fault Responses All Faults
COMMAND NAME CMD CODE DESCRIPTION TYPE PAGED
DATA
FORMAT UNITS NVM
DEFAULT
VALUE
MFR_RETRY_ DELAY 0xDB Retry interval during FAULT retry mode. R/W Word Y L11 ms Y 350
0xFABC
MFR_RETRY_DELAY
This command sets the time in milliseconds between restarts if the fault response is to retry the controller at specified
intervals. This command value is used for all fault responses that require retry. The retry time starts once the fault has
been detected by the offending channel. Valid values are from 120ms to 83.88 seconds in 10µs increments.
Note: The retry delay time is determined by the longer of the MFR_RETRY_DELAY command or the time required
for the regulated output to decay below 12.5% of the programmed value. If the natural decay time of the output is
too long, it is possible to remove the voltage requirement of the MFR_RETRY_DELAY command by asserting bit 0 of
MFR_CHAN_CONFIG_LTC3880.
This command has two data bytes and is formatted in Linear_5s_11s format.
Fault Responses Input Voltage
COMMAND NAME CMD CODE DESCRIPTION TYPE PAGED
DATA
FORMAT UNITS NVM
DEFAULT
VALUE
VIN_OV_FAULT_RESPONSE 0x56 Action to be taken by the device when an
input supply overvoltage fault is detected.
R/W Byte Y Reg Y 0x80
VIN_OV_FAULT_RESPONSE
The VIN_OV_FAULT_RESPONSE command instructs the device on what action to take in response to an input over-
voltage fault. The data byte is in the format given in Table 9.
The device also:
• Sets the NONE_OF_THE_ABOVE bit in the STATUS_BYTE
• Set the INPUT bit in the upper byte of the STATUS_WORD
LTC3880/LTC3880-1
81
3880fg
For more information www.linear.com/LTC3880
PMBus
COMMAND DETAILS
• Sets the VIN Overvoltage Fault bit in the STATUS_INPUT command, and
• Notifies the host by asserting ALERT pin
This command has one data byte.
Fault Responses Output Voltage
COMMAND NAME CMD CODE DESCRIPTION TYPE PAGED
DATA
FORMAT UNITS NVM
DEFAULT
VALUE
VOUT_OV_FAULT_RESPONSE 0x41 Action to be taken by the device when an
output overvoltage fault is detected.
R/W Byte Y Reg Y 0xB8
VOUT_UV_FAULT_RESPONSE 0x45 Action to be taken by the device when an
output undervoltage fault is detected.
R/W Byte Y Reg Y 0xB8
TON_MAX_FAULT_
RESPONSE
0x63 Action to be taken by the device when a
TON_MAX_FAULT event is detected.
R/W Byte Y Reg Y 0xB8
VOUT_OV_FAULT_RESPONSE
The VOUT_OV_FAULT_RESPONSE command instructs the device on what action to take in response to an output
overvoltage fault. The data byte is in the format given in Table 5.
The device also:
• Sets the VOUT_OV bit in the STATUS_BYTE
• Sets the VOUT bit in the STATUS_WORD
• Sets the VOUT Overvoltage Fault bit in the STATUS_VOUT command
• Notifies the host by asserting ALERT pin
The only value recognized for this command are:
0x80–The device shuts down (disables the output) and the unit does not attempt to retry. The output remains disabled
until the fault is cleared (PMBus, Part II, Section 10.7).
0xB8–The device shuts down (disables the output) and device attempts retry continuously, without limitation, until
it is commanded OFF (by the RUN pin or OPERATION command or both), bias power is removed, or another fault
condition causes the unit to shut down.
0x4n The device shuts down and the unit does not attempt to retry. The output remains disabled until the part is com-
manded OFF then ON or the RUN pin is asserted low then high or RESET through the command or removal of VIN.
The OV fault must remain active for a period of n • 10µs, where n is a value from 0 to 7.
0x78+n The device shuts down and the unit attempts to retry continuously until either the fault condition is cleared
or the part is commanded OFF then ON or the RUN pin is asserted low then high or RESET through the command or
removal of VIN. The OV fault must remain active for a period of n • 10µs, where n is a value from 0 to 7.
Any other value will result in a CML fault and the write will be ignored.
This command has one data byte.
LTC3880/LTC3880-1
82
3880fg
For more information www.linear.com/LTC3880
PMBus
COMMAND DETAILS
Table 5. VOUT_OV_FAULT_RESPONSE Data Byte Contents
BITS DESCRIPTION VALUE MEANING
7:6 Response
For all values of bits [7:6], the LTC3880:
• Sets the corresponding fault bit in the status commands and
• Notifies the host by asserting ALERT pin
The fault bit, once set, is cleared only when one or more of the
following events occurs:
• The device receives a CLEAR_FAULTS command.
• The output is commanded through the RUNn pin, the
OPERATION command, or the combined action of the RUNn pin
and OPERATION command, to turn off and then to turn back on,
or
• Bias power is removed and reapplied to the LTC3880.
00 Part performs OV pull down only (i.e., turns off the top
MOSFET and turns on lower MOSFET while VOUT is >
VOUT_OV_FAULT)
01 The PMBus device continues operation for the delay time
specified by bits [2:0] and the delay time unit specified for that
particular fault. If the fault condition is still present at the end of
the delay time, the unit responds as programmed in the Retry
Setting (bits [5:3]).
10 The device shuts down immediately (disables the output) and
responds according to the retry setting in bits [5:3].
11 Not supported. Writing this value will generate a CML fault.
5:3 Retry Setting 000-110 The unit does not attempt to restart. The output remains
disabled until the fault is cleared until the device is commanded
OFF bias power is removed.
111 The PMBus device attempts to restart continuously, without
limitation, until it is commanded OFF (by the RUNn pin or
OPERATION command or both), bias power is removed, or
another fault condition causes the unit to shut down without
retry. Note: The retry interval is set by the MFR_RETRY_DELAY
command.
2:0 Delay Time XXX The delay time in 10µs increments. This delay time determines
how long the controller continues operating after a fault is
detected. Only valid for deglitched off state
VOUT_UV_FAULT_RESPONSE
The VOUT_UV_FAULT_RESPONSE command instructs the device on what action to take in response to an output
undervoltage fault. The data byte is in the format given in Table 6.
The device also:
• Sets the VOUT bit in the STATUS_WORD
• Sets the VOUT undervoltage fault bit in the STATUS_VOUT command
• Notifies the host by asserting ALERT pin
The UV fault and warn are masked until the following criteria are achieved:
1) The TON_MAX_FAULT_LIMIT has been reached
2) The TON_DELAY sequence has completed
3) The TON_RISE sequence has completed
4) The VOUT_UV_FAULT_LIMIT threshold has been reached
5) The IOUT_OC_FAULT_LIMIT is not present
The UV fault and warn are masked whenever the channel is not active.
The UV fault and warn are masked during TON_RISE and TOFF_FALL sequencing.
This command has one data byte.
LTC3880/LTC3880-1
83
3880fg
For more information www.linear.com/LTC3880
PMBus
COMMAND DETAILS
Table 6. VOUT_UV_FAULT_RESPONSE Data Byte Contents
BITS DESCRIPTION VALUE MEANING
7:6 Response
For all values of bits [7:6], the LTC3880:
• Sets the corresponding fault bit in the status commands and
• Notifies the host by asserting ALERT pin
The fault bit, once set, is cleared only when one or more of the
following events occurs:
• The device receives a CLEAR_FAULTS command
• The output is commanded through the RUNn pin, the
OPERATION command, or the combined action of the RUNn pin
and OPERATION command, to turn off and then to turn back on,
or
• Bias power is removed and reapplied to the LTC3880
00 The PMBus device continues operation without interruption.
(Ignores the fault functionally)
01 The PMBus device continues operation for the delay time
specified by bits [2:0] and the delay time unit specified for
that particular fault. If the fault condition is still present at the
end of the delay time, the unit responds as programmed in the
Retry Setting (bits [5:3]).
10 The device shuts down (disables the output) and responds
according to the retry setting in bits [5:3].
11 Not supported. Writing this value will generate a CML fault.
5:3 Retry Setting 000-110 The unit does not attempt to restart. The output remains
disabled until the fault is cleared until the device is commanded
OFF bias power is removed.
111 The PMBus device attempts to restart continuously, without
limitation, until it is commanded OFF (by the RUNn pin or
OPERATION command or both), bias power is removed, or
another fault condition causes the unit to shut down without
retry. Note: The retry interval is set by the MFR_RETRY_DELAY
command.
2:0 Delay Time XXX The delay time in 10µs increments. This delay time determines
how long the controller continues operating after a fault is
detected. Only valid for deglitched off state.
TON_MAX_FAULT_RESPONSE
The TON_MAX_FAULT_RESPONSE command instructs the device on what action to take in response to a TON_MAX
fault. The data byte is in the format given in Table 9.
The device also:
• Sets the NONE_OF_THE_ABOVE bit in the STATUS_BYTE
• Sets the VOUT bit in the STATUS_WORD
• Sets the TON_MAX_FAULT bit in the STATUS_VOUT command, and
• Notifies the host by asserting ALERT pin
• A value of 0 disables the TON_MAX_FAULT_RESPONSE. It is not recommended to use 0.
This command has one data byte.
LTC3880/LTC3880-1
84
3880fg
For more information www.linear.com/LTC3880
Fault Responses Output Current
COMMAND NAME CMD CODE DESCRIPTION TYPE PAGED
DATA
FORMAT UNITS NVM
DEFAULT
VALUE
IOUT_OC_FAULT_RESPONSE 0x47 Action to be taken by the device when an
output overcurrent fault is detected.
R/W Byte Y Reg Y 0x00
IOUT_OC_FAULT_RESPONSE
The IOUT_OC_FAULT_RESPONSE command instructs the device on what action to take in response to an output
overcurrent fault. The data byte is in the format given in Table 7.
The device also:
• Sets the IOUT_OC bit in the STATUS_BYTE
• Sets the IOUT bit in the STATUS_WORD
• Sets the IOUT Overcurrent Fault bit in the STATUS_IOUT command, and
• Notifies the host by asserting ALERT pin
This command has one data byte.
Table 7. IOUT_OC_FAULT_RESPONSE Data Byte Contents
BITS DESCRIPTION VALUE MEANING
7:6 Response
For all values of bits [7:6], the LTC3880:
• Sets the corresponding fault bit in the status commands and
• Notifies the host by asserting ALERT pin
The fault bit, once set, is cleared only when one or more of the
following events occurs:
• The device receives a CLEAR_FAULTS command
• The output is commanded through the RUNn pin, the
OPERATION command, or the combined action of the RUNn pin
and OPERATION command, to turn off and then to turn back on,
or
• Bias power is removed and reapplied to the LTC3880.
00 The LTC3880 continues to operate indefinitely while maintaining
the output current at the value set by IOUT_OC_FAULT_LIMIT
without regard to the output voltage (known as constant-
current or brick-wall limiting).
01 Not supported.
10 The LTC3880 continues to operate, maintaining the output
current at the value set by IOUT_OC_FAULT_LIMIT without
regard to the output voltage, for the delay time set by bits [2:0].
If the device is still operating in current limit at the end of the
delay time, the device responds as programmed by the Retry
Setting in bits [5:3].
11 The LTC3880 shuts down immediately and responds as
programmed by the Retry Setting in bits [5:3].
5:3 Retry Setting 000-110 The unit does not attempt to restart. The output remains
disabled until the fault is cleared by cycling the RUNn pin or
removing bias power.
111 The device attempts to restart continuously, without limitation,
until it is commanded OFF (by the RUNn pin or OPERATION
command or both), bias power is removed, or another fault
condition causes the unit to shut down. Note: The retry interval
is set by the MFR_RETRY_DELAY command.
2:0 Delay Time XXX The number of delay time units in 16ms increments. This
delay time is used to determine the amount of time a unit is
to continue operating after a fault is detected before shutting
down. Only valid for deglitched off state.
PMBus
COMMAND DETAILS
LTC3880/LTC3880-1
85
3880fg
For more information www.linear.com/LTC3880
Fault Responses IC Temperature
COMMAND NAME CMD CODE DESCRIPTION TYPE PAGED
DATA
FORMAT UNITS NVM
DEFAULT
VALUE
MFR_OT_FAULT_
RESPONSE
0xD6 Action to be taken by the device when an
internal overtemperature fault is detected
R Byte N Reg 0xC0
MFR_OT_FAULT_RESPONSE
The MFR_OT_FAULT_RESPONSE command byte instructs the device on what action to take in response to an internal
overtemperature fault. The data byte is in the format given in Table 8.
The LTC3880 also:
• Sets the MFR bit in the STATUS_WORD, and
• Sets the Overtemperature Fault bit in the STATUS_MFR_SPECIFIC command
• Notifies the host by asserting ALERT pin
This command has one data byte.
Table 8. Data Byte Contents MFR_OT_FAULT_RESPONSE
BITS DESCRIPTION VALUE MEANING
7:6 Response
For all values of bits [7:6], the LTC3880:
• Sets the corresponding fault bit in the status commands and
• Notifies the host by asserting ALERT pin
The fault bit, once set, is cleared only when one or more of the
following events occurs:
• The device receives a CLEAR_FAULTS command
• The output is commanded through the RUNn pin, the
OPERATION command, or the combined action of the RUNn pin
and OPERATION command, to turn off and then to turn back on,
or
• Bias power is removed and reapplied to the LTC3880
00 Not supported. Writing this value will generate a CML fault.
01 Not supported. Writing this value will generate a CML fault
10 The device shuts down immediately (disables the output) and
responds according to the retry setting in bits [5:3].
11 The device’s output is disabled while the fault is present.
Operation resumes and the output is enabled when the fault
condition no longer exists.
5:3 Retry Setting 000 The unit does not attempt to restart. The output remains
disabled until the fault is cleared.
001-111 Not supported. Writing this value will generate CML fault.
2:0 Delay Time XXX Not supported. Value ignored
PMBus
COMMAND DETAILS
LTC3880/LTC3880-1
86
3880fg
For more information www.linear.com/LTC3880
Fault Responses External Temperature
COMMAND NAME CMD CODE DESCRIPTION TYPE PAGED
DATA
FORMAT UNITS NVM
DEFAULT
VALUE
OT_FAULT_ RESPONSE 0x50 Action to be taken by the device when an external
overtemperature fault is detected,
R/W Byte Y Reg Y 0xB8
UT_FAULT_ RESPONSE 0x54 Action to be taken by the device when an external
undertemperature fault is detected.
R/W Byte Y Reg Y 0xB8
OT_FAULT_RESPONSE
The OT_FAULT_RESPONSE command instructs the device on what action to take in response to an external overtem-
perature fault on the external temp sensors. The data byte is in the format given in Table 9.
The device also:
• Sets the TEMPERATURE bit in the STATUS_BYTE
• Sets the Overtemperature Fault bit in the STATUS_TEMPERATURE command, and
• Notifies the host by asserting ALERT pin
This condition is detected by the ADC so the response time may be up to 90ms.
This command has one data byte.
UT_FAULT_RESPONSE
The UT_FAULT_RESPONSE command instructs the device on what action to take in response to an external under-
temperature fault on the external temp sensors. The data byte is in the format given in Table 9.
The device also:
• Sets the TEMPERATURE bit in the STATUS_BYTE
• Sets the Undertemperature Fault bit in the STATUS_TEMPERATURE command, and
• Notifies the host by asserting ALERT pin
This condition is detected by the ADC so the response time may be up to 90ms.
This command has one data byte.
PMBus
COMMAND DETAILS
LTC3880/LTC3880-1
87
3880fg
For more information www.linear.com/LTC3880
Table 9. Data Byte Contents: TON_MAX_FAULT_RESPONSE, VIN_OV_FAULT_RESPONSE,
OT_FAULT_RESPONSE, UT_FAULT_RESPONSE
BITS DESCRIPTION VALUE MEANING
7:6 Response
For all values of bits [7:6], the LTC3880:
• Sets the corresponding fault bit in the status commands, and
• Notifies the host by asserting ALERT pin
The fault bit, once set, is cleared only when one or more of the
following events occurs:
• The device receives a CLEAR_FAULTS command
• The output is commanded through the RUNn pin, the
OPERATION command, or the combined action of the RUNn pin
and OPERATION command, to turn off and then to turn back on,
or
• Bias power is removed and reapplied to the LTC3880
00 The PMBus device continues operation without interruption.
01 Not supported. Writing this value will generate a CML fault.
10 The device shuts down immediately (disables the output) and
responds according to the retry setting in bits [5:3].
11 Not supported. Writing this value will generate a CML fault.
5:3 Retry Setting 000-110 The unit does not attempt to restart. The output remains
disabled until the fault is cleared until the device is commanded
OFF bias power is removed.
111 The PMBus device attempts to restart continuously, without
limitation, until it is commanded OFF (by the RUNn pin or
OPERATION command or both), bias power is removed, or
another fault condition causes the unit to shut down without
retry. Note: The retry interval is set by the MFR_RETRY_DELAY
command.
2:0 Delay Time XXX Not supported. Values ignored
FAULT SHARING
Fault Sharing Propagation
COMMAND NAME CMD CODE DESCRIPTION TYPE PAGED
DATA
FORMAT UNITS NVM
DEFAULT
VALUE
MFR_GPIO_
PROPAGATE_LTC 3880
0xD2 Configuration that determines which faults are
propagated to the GPIO pins.
R/W Word Y Reg Y 0x2993
MFR_GPIO_PROPAGATE_LTC3880
The MFR_GPIO_PROPAGATE_LTC3880 command enables the faults that can cause the GPIOn pin to assert low. The
command is formatted as shown in Table 10. Faults can only be propagated to the GPIO if they are programmed to
respond to faults.
This command has two data bytes.
Table 10: GPIOn Propagate Fault Configuration
The GPIO0 and GPIO1 pins are designed to provide electrical notification of selected events to the user. Some of these events are common to both output
channels. Others are specific to an output channel. They can also be used to share faults between channels.
BIT(S) SYMBOL OPERATION
B[15] VOUT disabled while not decayed. This is used in a PolyPhase configuration when bit 0 of the MFR_CHAN_CONFIG_LT C 3880 is a
zero. If the channel is turned off, by toggling the RUN pin or commanding the part OFF, and then
the RUN is reasserted or the part is commanded back on before the output has decayed, VOUT
will not restart until the 12.5% decay is honored. The GPIO pin is asserted during this condition if
bit 15 is asserted.
PMBus
COMMAND DETAILS
LTC3880/LTC3880-1
88
3880fg
For more information www.linear.com/LTC3880
BIT(S) SYMBOL OPERATION
B[14] Mfr_gpio_propagate_short_CMD_cycle 0: No action
1: Asserts low if commanded off then on before the output has sequenced off. Re-asserts high
120ms after sequence off.
b[13] Mfr_gpio_propagate_ton_max_fault 0: No action if a TON_MAX_FAULT fault is asserted
1: Associated output will be asserted low if a TON_MAX_FAULT fault is asserted
GPIO0 is associated with page 0 TON_MAX_FAULT faults
GPIO1 is associated with page 1 TON_MAX_FAULT faults
b[12] Mfr_gpio0_propagate_vout_uvuf,
Mfr_gpio1_propagate_vout_uvuf
Unfiltered VOUT_UV_FAULT_LIMIT (PGOOD) comparator output
GPIO0 is associated with channel 0
GPIO1 is associated with channel 1
b[11] Mfr_gpio0_propagate_int_ot,
Mfr_gpio1_propagate_int_ot
0: No action if the MFR_OT_FAULT_LIMIT fault is asserted
1: Associated output will be asserted low if the MFR_OT_FAULT_LIMIT fault is asserted
b[10] Reserved Always set to 0
b[9] Reserved Always set to 0
b[8] Mfr_gpio0_propagate_ut,
Mfr_gpio1_propagate_ut
0: No action if the UT_FAULT_LIMIT fault is asserted
1: Associated output will be asserted low if the UT_FAULT_LIMIT fault is asserted
GPIO0 is associated with page 0 UT faults
GPIO1 is associated with page 1 UT faults
b[7] Mfr_gpio0_propagate_ot,
Mfr_gpio1_propagate_ot
0: No action if the OT_FAULT_LIMIT fault is asserted
1: Associated output will be asserted low if the OT_FAULT_LIMIT fault is asserted
GPIO0 is associated with page 0 OT faults
GPIO1 is associated with page 1 OT faults
b[6] Reserved
b[5] Reserved
b[4] Mfr_gpio0_propagate_input_ov,
Mfr_gpio1_propagate_input_ov
0: No action if the VIN_OV_FAULT_LIMIT fault is asserted
1: Associated output will be asserted low if the VIN_OV_FAULT_LIMIT fault is asserted
b[3] Reserved
b[2] Mfr_gpio0_propagate_iout_oc,
Mfr_gpio1_propagate_iout_oc
0: No action if the IOUT_OC_FAULT_LIMIT fault is asserted
1: Associated output will be asserted low if the IOUT_OC_FAULT_LIMIT fault is asserted
GPIO0 is associated with page 0 OC faults
GPIO1 is associated with page 1 OC faults
b[1] Mfr_gpio0_propagate_vout_uv,
Mfr_gpio1_propagate_vout_uv
0: No action if the VOUT_UV_FAULT_LIMIT fault is asserted
1: Associated output will be asserted low if the VOUT_UV_FAULT_LIMIT fault is asserted
GPIO0 is associated with page 0 UV faults
GPIO1 is associated with page 1 UV faults
b[0] Mfr_gpio0_propagate_vout_ov,
Mfr_gpio1_propagate_vout_ov
0: No action if the VOUT_OV_FAULT_LIMIT fault is asserted
1: Associated output will be asserted low if the VOUT_OV_FAULT_LIMIT fault is asserted
GPIO0 is associated with page 0 OV faults
GPIO1 is associated with page 1 OV faults
Note 1: The PWRGD status is designed as an indicator and not to be used for power supply sequencing.
PMBus
COMMAND DETAILS
LTC3880/LTC3880-1
89
3880fg
For more information www.linear.com/LTC3880
Fault Sharing Response
COMMAND NAME CMD CODE DESCRIPTION TYPE PAGED
DATA
FORMAT UNITS NVM
DEFAULT
VALUE
MFR_GPIO_RESPONSE 0xD5 Action to be taken by the device when the GPIO pin
is asserted low.
R/W Byte Y Reg Y 0xC0
MFR_GPIO_RESPONSE
This command determines the controller’s response to the GPIOn pin being pulled low by an external source.
VALUE MEANING
0xC0 GPIO_INHIBIT The LTC3880 will three-state the output in response to the GPIO pin pulled low.
0x00 GPIO_IGNORE The LTC3880 continues operation without interruption.
The device also:
• Sets the NONE_OF_THE_ABOVE bit in the STATUS_BYTE
• Sets the MFR bit in the STATUS_WORD
• Sets the GPIOB bit in the STATUS_MFR_SPECIFIC command, and
• Notifies the host by asserting ALERT pin. The ALERT pin pulled low can be disabled by setting bit[1] of MFR_CHAN_
CFG_LTC3880.
This command has one data byte.
SCRATCHPAD
COMMAND NAME CMD CODE DESCRIPTION TYPE PAGED
DATA
FORMAT UNITS NVM
DEFAULT
VALUE
USER_DATA_00 0xB0 OEM reserved. Typically used for part serialization. R/W Word N Reg Y NA
USER_DATA_01 0xB1 Manufacturer reserved for LTpowerPlay. R/W Word Y Reg Y NA
USER_DATA_02 0xB2 OEM reserved. Typically used for part serialization. R/W Word N Reg Y NA
USER_DATA_03 0xB3 A NVM word available for the user. R/W Word Y Reg Y 0x0000
USER_DATA_04 0xB4 A NVM word available for the user. R/W Word N Reg Y 0x0000
USER_DATA_00 through USER_DATA_04
These commands are non-volatile memory locations for customer storage. The customer has the option to write any
value to the USER_DATA_nn at any time. However, the LTpowerPlay software and contract manufacturers use some
of these commands for inventory control. Modifying the reserved USER_DATA_nn commands may lead to undesirable
inventory control and incompatibility with these products.
These commands have 2 data bytes and are in register format.
PMBus
COMMAND DETAILS
LTC3880/LTC3880-1
90
3880fg
For more information www.linear.com/LTC3880
IDENTIFICATION
COMMAND NAME CMD CODE DESCRIPTION TYPE PAGED
DATA
FORMAT UNITS NVM
DEFAULT
VALUE
PMBUS_REVISION 0x98 PMBus revision supported by this device. Current revision
is 1.1.
R Byte N Reg 0x11
CAPABILITY 0x19 Summary of PMBus optional communication protocols
supported by this device.
R Byte N Reg 0xB0
MFR_ID 0x99 The manufacturer ID of the LTC3880 in ASCII. R String N ASC LTC
MFR_MODEL 0x9A Manufacturer part number in ASCII. R String N ASC LTC3880
MFR_SERIAL 0x9E Serial number of this specific unit in ASCII. R Block N CF NA
MFR_SPECIAL_ID 0xE7 Manufacturer code representing the LTC3880. R Word N Reg 402x
PMBus_REVISION
The PMBUS_REVISION command indicates the revision of the PMBus to which the device is compliant. The LTC3880
is PMBus Version 1.1 compliant in both Part I and Part II.
This read-only command has one data byte.
CAPABILITY
This command provides a way for a host system to determine some key capabilities of a PMBus device.
The LTC3880 supports packet error checking, 400kHz bus speeds, and ALERT pin.
This read-only command has one data byte.
MFR_ID
The MFR_ID command indicates the manufacturer ID of the LTC3880 using ASCII characters.
This read-only command is in block format.
MFR_MODEL
The MFR_MODEL command indicates the manufacturer’s part number of the LTC3880 using ASCII characters.
This read-only command is in block format.
MFR_SERIAL
The MFR_SERIAL command contains up to 9 bytes of custom formatted data used to uniquely identify the LTC3880
configuration.
This read-only command is in block format.
MFR_SPECIAL_ID
The 16-bit word representing the part name. 0x402 denotes the part is an LTC3880, X is adjustable by the manufacturer.
This read-only command has 2 data bytes.
PMBus
COMMAND DETAILS
LTC3880/LTC3880-1
91
3880fg
For more information www.linear.com/LTC3880
FAULT WARNING AND STATUS
COMMAND NAME CMD CODE DESCRIPTION TYPE PAGED FORMAT UNITS NVM
DEFAULT
VALUE
CLEAR_FAULTS 0x03 Clear any fault bits that have been set. Send Byte N NA
MFR_CLEAR_PEAKS 0xE3 Clears all peaks values. Send Byte N NA
STATUS_BYTE 0x78 One byte summary of the unit’s fault
condition.
R/W Byte Y Reg NA
STATUS_WORD 0x79 Tw o byte summary of the unit’s fault condition. R/W Word Y Reg NA
STATUS_VOUT 0x7A Output voltage fault and warning status. R/W Byte Y Reg NA
STATUS_IOUT 0x7B Output current fault and warning status. R/W Byte Y Reg NA
STATUS_INPUT 0x7C Input supply fault and warning status. R/W Byte N Reg NA
STATUS_ TEMPERATURE 0x7D External temperature fault and warning status
for READ_TEMERATURE_1.
R/W Byte Y Reg NA
STATUS_CML 0x7E Communication and memory fault and
warning status.
R/W Byte N Reg NA
STATUS_MFR_ SPECIFIC 0x80 Manufacturer specific fault and state
information.
R/W Byte Y Reg NA
MFR_PADS 0xE5 Digital status of the I/O pads. R Word N Reg NA
MFR_COMMON 0xEF Manufacturer status bits that are common
across multiple LTC chips.
R Byte N Reg NA
MFR_INFO 0xB6 Manufacturing specific information R Byte N Reg NA
CLEAR_FAULTS
The CLEAR_FAULTS command is used to clear any fault bits that have been set. This command clears all bits in all
status commands simultaneously. At the same time, the device negates (clears, releases) its ALERT pin signal output
if the device is asserting the ALERT pin signal.
The CLEAR_FAULTS does not cause a unit that has latched off for a fault condition to restart. Units that have shut down
for a fault condition are restarted when:
• The output is commanded through the RUN pin, the OPERATION command, or the combined action of the RUN pin
and OPERATION command, to turn off and then to turn back on, or
• MFR_RESET command is issued.
• Bias power is removed and reapplied to the integrated circuit
If the fault is still present when the bit is cleared, the fault bit will remain set and the host notified by asserting the
ALERT pin pin low. CLEAR_FAULTS can take up to 10µs to process. If a fault occurs within that time frame it may be
cleared before the status register is set.
This write-only command has no data bytes.
MFR_CLEAR_PEAKS
The MFR_CLEAR_PEAKS command clears the MFR_*_PEAK data values. A reset will initiate this command.
This write-only command has no data bytes.
PMBus
COMMAND DETAILS
LTC3880/LTC3880-1
92
3880fg
For more information www.linear.com/LTC3880
STATUS_BYTE
The STATUS_BYTE command returns a one-byte summary of the most critical faults.
STATUS_BYTE Message Contents:
BIT STATUS BIT NAME MEANING
7* BUSY A fault was declared because the LTC3880 was unable to respond.
6 OFF This bit is set if the channel is not providing power to its output, regardless of the reason, including simply not
being enabled.
5 VOUT_OV An output overvoltage fault has occurred.
4 IOUT_OC An output overcurrent fault has occurred.
3 VIN_UV Not supported (LTC3880 returns 0).
2 TEMPERATURE A temperature fault or warning has occurred.
1 CML A communications, memory or logic fault has occurred.
0* NONE OF THE ABOVE A fault Not listed in bits[7:1] has occurred.
Any supported fault bit in this command will initiate an ALERT event.
This command has one data byte.
STATUS_WORD
The STATUS_WORD command returns a two-byte summary of the channel’s fault condition. The low byte of the
STATUS_WORD is typically the same as the STATUS_BYTE command: However, if a fault occurs at the exact right
time, the read value can have a bit set in the lower byte with no corresponding bits set in the upper byte. An immediate
second read of STATUS_WORD will have the corresponding bits in the upper byte set.
STATUS_WORD High Byte Message Contents:
BIT STATUS BIT NAME MEANING
15 VOUT An output voltage fault or warning has occurred.
14 IOUT An output current fault or warning has occurred.
13 INPUT An input voltage fault or warning has occurred.
12 MFR_SPECIFIC A fault or warning specific to the LTC3880 has occurred.
11 POWER_GOOD# The POWER_GOOD state is false if this bit is set.
10 FANS Not supported (LTC3880 returns 0).
9 OTHER Not supported (LTC3880 returns 0).
8 UNKNOWN Not supported (LTC3880 returns 0).
Any supported fault bit in this command will initiate an ALERT event.
This command has two data bytes.
PMBus
COMMAND DETAILS
LTC3880/LTC3880-1
93
3880fg
For more information www.linear.com/LTC3880
STATUS_VOUT
The STATUS_VOUT commands returns one byte of VOUT status information
.
STATUS_VOUT Message Contents:
BIT MEANING
7 VOUT overvoltage fault.
6 VOUT overvoltage warning.
5 VOUT undervoltage warning.
4 VOUT undervoltage fault.
3 VOUT_MAX warning.
2 TON_MAX fault.
1 TOFF_MAX warning.
0 Not supported by the LTC3880 (returns 0).
ALERT can be asserted if any of bits[7:1] are set. These may be cleared by writing a 1 to their bit position in STATUS_VOUT, in lieu of a CLEAR_FAULTS
command.
This command has one data byte.
STATUS_IOUT
The STATUS_IOUT commands returns one byte of IOUT status information.
STATUS_IOUT Message Contents:
BIT MEANING
7 IOUT overcurrent fault.
6 Not supported (LTC3880 returns 0).
5 IOUT overcurrent warning.
4:0 Not supported (LTC3880 returns 0).
ALERT can be asserted if any supported bits are set. Any supported bit may be cleared by writing a 1 to that bit position in STATUS_IOUT, in lieu of a
CLEAR_FAULTS command.
This command has one data byte.
PMBus
COMMAND DETAILS
LTC3880/LTC3880-1
94
3880fg
For more information www.linear.com/LTC3880
STATUS_INPUT
The STATUS_INPUT commands returns one byte of VIN (VINSNS) status information.
STATUS_INPUT Message Contents:
BIT MEANING
7 VIN overvoltage fault.
6 Not supported (LTC3880 returns 0).
5 VIN undervoltage warning.
4 Not supported (LTC3880 returns 0).
3 Unit off for insufficient VIN.
2 Not supported (LTC3880 returns 0).
1 Input over current warning.
0 Not supported (LTC3880 returns 0)
ALERT can be asserted if bit 7 is set. Bit 7 may be cleared by writing it to a 1, in lieu of a CLEAR_FAULTS command.
This command has one data byte.
STATUS_TEMPERATURE
The STATUS_TEMPERATURE commands returns one byte of sensed external temperature status information.
STATUS_TEMPERATURE Message Contents:
BIT MEANING
7 External overtemperature fault.
6 External overtemperature warning.
5 Not supported (LTC3880 returns 0).
4 External undertemperature fault.
3:0 Not supported (LTC3880 returns 0).
ALERT can be asserted if any supported bits are set. Any supported bit may be cleared by writing a 1 to that bit position in STATUS_TEMPERATURE, in
lieu of a CLEAR_FAULTS command.
This command has one data byte.
PMBus
COMMAND DETAILS
LTC3880/LTC3880-1
95
3880fg
For more information www.linear.com/LTC3880
PMBus
COMMAND DETAILS
STATUS_CML
The STATUS_CML commands returns one byte of status information on received commands, internal memory and logic.
STATUS_CML Message Contents:
BIT MEANING
7 Invalid or unsupported command received.
6 Invalid or unsupported data received.
5 Packet error check failed.
4 Memory fault detected.
3 Processor fault detected.
2 Reserved (LTC3880 returns 0).
1 Other communication fault.
0 Other memory or logic fault.
ALERT can be asserted if any supported bits are set. Any supported bit may be cleared by writing a 1 to that bit position in STATUS_CML, in lieu of a
CLEAR_FAULTS command.
This command has one data byte.
STATUS_MFR_SPECIFIC
The STATUS_MFR_SPECIFIC commands returns one byte with the manufacturer specific status information.
Each channel has a copy of the same information. Only bit 0 is page specific.
The format for this byte is:
BIT MEANING
7 Internal Temperature Fault Limit Exceeded.
6 Internal Temperature Warn Limit Exceeded.
5 NVM CRC Fault.
4 PLL is Unlocked
3 Fault Log Present
2 VDD33 UV or OV Fault
0GPIO Pin Asserted Low by External Device (paged)
If any of these bits are set, the MFR bit in the STATUS_WORD will be set.
The user is permitted to write a 1 to any bit in this command to clear a specific fault. This permits the user to clear
status by means other than using the CLEAR_FAULTS command. Exception: The fault log present bit can only be
cleared by issuing the MFR_FAULT_LOG_CLEAR command.
Any supported fault bit in this command will initiate an ALERT event.
This command has one data byte.
LTC3880/LTC3880-1
96
3880fg
For more information www.linear.com/LTC3880
PMBus
COMMAND DETAILS
Summary of the Status Registers
(PAGED)
MFR_PADS_LTC3880
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
VDD33 0V
VDD33 UV
(reads 0)
(reads 0)
Invalid ADC Result(s)
SYNC Output Disabled Externally
Channel 1 is POWER_GOOD
Channel 0 is POWER_GOOD
LTC3880 Forcing RUN1 Low
LTC3880 Forcing RUN0 Low
RUN1 Pin State
RUN0 Pin State
LTC3880 Forcing GPIO1 Low
LTC3880 Forcing GPIO0 Low
GPIO1 Pin State
GPIO0 Pin State
STATUS_MFR_SPECIFIC
7
6
5
4
3
2
1
0
(PAGED)
3880 SR01
STATUS_INPUT
7
6
5
4
3
2
1
0
MFR_INFO
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
Reserved
Reserved
Reserved
Reserved
Reserved
Reserved
Reserved
Reserved
Reserved
Reserved
Reserved
EEPROM ECC Status
Reserved
Reserved
Reserved
Reserved
STATUS_WORD
STATUS_BYTE
7
6
5
4
3
2
1
0
(PAGED)
MFR_COMMON
7
6
5
4
3
2
1
0
Chip Not Driving ALERT Low
Chip Not Busy
Internal Calculations Not Pending
Output Not In Transition
EEPROM Initialized
(reads 0)
SHARE_CLK_LOW
WP Pin High
STATUS_TEMPERATURE
7
6
5
4
3
2
1
0
STATUS_CML
7
6
5
4
3
2
1
0
STATUS_VOUT*
7
6
5
4
3
2
1
0
(PAGED)
STATUS_IOUT
7
6
5
4
3
2
1
0
(PAGED)
MASKABLEDESCRIPTION
General Fault or Warning Event
Dynamic
Status Derived from Other Bits
Yes
No
No
GENERATES ALERT
Yes
No
Not Directly
BIT CLEARABLE
Yes
No
No
VOUT_OV Fault
VOUT_OV Warning
VOUT_UV Warning
VOUT_UV Fault
VOUT_MAX Warning
TON_MAX Fault
TOFF_MAX Warning
(reads 0)
IOUT_OC Fault
(reads 0)
IOUT_OC Warning
(reads 0)
(reads 0)
(reads 0)
(reads 0)
(reads 0)
OT Fault
OT Warning
(reads 0)
UT Fault
(reads 0)
(reads 0)
(reads 0)
(reads 0)
Invalid/Unsupported Command
Invalid/Unsupported Data
Packet Error Check Failed
Memory Fault Detected
Processor Fault Detected
(reads 0)
Other Communication Fault
Other Memory or Logic Fault
Internal Temperature Fault
Internal Temperature Warning
EEPROM CRC Error
Internal PLL Unlocked
Fault Log Present
(reads 0)
VOUT Short Cycled
GPIO Pulled Low By External Device
VIN_OV Fault
(reads 0)
VIN_UV Warning
(reads 0)
Unit Off for Insuffcient VIN
(reads 0)
IIN_OC Warning
(reads 0)
15
14
13
12
11
10
9
8
VOUT
IOUT
INPUT
MFR_SPECIFIC
POWER_GOOD#
(reads 0)
(reads 0)
(reads 0)
BUSY
OFF
VOUT_OV
IOUT_OC
(reads 0)
TEMPERATURE
CML
NONE OF THE ABOVE
LTC3880/LTC3880-1
97
3880fg
For more information www.linear.com/LTC3880
PMBus
COMMAND DETAILS
MFR_PADS
This command provides the user a means of directly reading the digital status of the I/O pins of the device. The bit
assignments of this command are as follows:
BIT ASSIGNED DIGITAL PIN
15 VDD33 OV Fault
14 VDD33 UV Fault
13 Reserved
12 Reserved
11 ADC Values Invalid, Occurs
During Start-Up
10 Device Driving ALERT Low
9 PowerGood1
8 PowerGood0
7 Device Driving RUN1 Low
6 Device Driving RUN0 Low
5 RUN1
4 RUN0
3 Device Driving GPIO1 Low
2 Device Driving GPIO0 Low
1GPIO1
0GPIO0
A 1 indicates the condition is true.
This read-only command has two data bytes.
MFR_COMMON
The MFR_COMMON command contains bits that are common to all LTC digital power and telemetry products.
BIT MEANING
7 CHIP NOT DRIVING ALERT LOW
6 CHIP NOT BUSY
5 CALCULATIONS NOT PENDING
4 OUTPUT NOT IN TRANSITION
3 NVM Initialized
2 Reserved
1 SHARE_CLK Timeout
0 WP Pin Status
This read-only command has one data byte.
LTC3880/LTC3880-1
98
3880fg
For more information www.linear.com/LTC3880
PMBus
COMMAND DETAILS
MFR_INFO
The MFR_INFO command contains additional status bits that are LTC3880-specific and may be common to multiple
LTC PSM products.
MFR_INFO Data Contents:
BIT MEANING
15:6 Reserved.
5 EEPROM ECC status.
0: Corrections made in the EEPROM user space.
1: No corrections made in the EEPROM user space.
4:0 Reserved
EEPROM ECC status is updated after each RESTORE_USER_ALL or RESET command, a power-on reset or an EEPROM
bulk read operation. This read-only command has two data bytes.
TELEMETRY
COMMAND NAME
CMD
CODE DESCRIPTION TYPE PAGED FORMAT UNITS NVM
DEFAULT
VALUE
READ_VIN 0x88 Measured input supply voltage. R Word N L11 V NA
READ_VOUT 0x8B Measured output voltage. R Word Y L16 V NA
READ_IIN 0x89 Calculated input supply current. R Word N L11 A NA
MFR_READ_IIN 0xED Calculated input current per channel. R Word Y L11 A NA
READ_IOUT 0x8C Measured output current. R Word Y L11 A NA
READ_TEMPERATURE_1 0x8D External diode junction temperature. This is the value
used for all temperature related processing, including
IOUT_CAL_GAIN.
R Word Y L11 C NA
READ_TEMPERATURE_2 0x8E Internal junction temperature. Does not affect any
other registers.
R Word N L11 C NA
READ_DUTY_CYCLE 0x94 Duty cycle of the top gate control signal. R Word Y L11 % NA
READ_POUT 0x96 Calculated output power. R Word Y L11 W NA
MFR_VOUT_PEAK 0xDD Maximum measured value of READ_VOUT since last
MFR_CLEAR_PEAKS.
R Word Y L16 V NA
MFR_VIN_PEAK 0xDE Maximum measured value of READ_VIN since last
MFR_CLEAR_PEAKS.
R Word N L11 V NA
MFR_TEMPERATURE_1_PEAK 0xDF Maximum measured value of external Temperature
(READ_TEMPERATURE_1) since last MFR_CLEAR_
PEAKS.
R Word Y L11 C NA
MFR_TEMPERATURE_2_PEAK 0xF4 Maximum measured value of external Temperature
(READ_TEMPERATURE_2) since last MFR_CLEAR_
PEAKS.
R Word N L11 C NA
MFR_IOUT_PEAK 0xD7 Report the maximum measured value of READ_IOUT
since last MFR_CLEAR_PEAKS.
R Word Y L11 A NA
READ_VIN
The READ_VIN command returns the measured input voltage, in volts.
This read-only command has two data bytes and is formatted in Linear_5s_11s format.
LTC3880/LTC3880-1
99
3880fg
For more information www.linear.com/LTC3880
READ_VOUT
The READ_VOUT command returns the measured output voltage in the same format as set by the VOUT_MODE
command.
This read-only command has two data bytes and is formatted in Linear_16u format.
READ_IIN
The READ_IIN command returns the input current in Amperes. Note: Input current is calculated from READ_IOUT
current and the READ_DUTY_CYCLE value from both outputs plus the MFR_IIN_OFFSET. For accurate values at low
currents the part must be in continuous conduction mode. The greatest source of error if DCR sensing is used, is the
accuracy of the inductor parasitic DC resistance (DCR) at room temperature IOUT_CAL_GAIN.
READ_IIN = MFR_READ_IIN_PAGE0 + MFR_READ_IIN_PAGE1
This read-only command has two data bytes and is formatted in Linear_5s_11s format.
MFR_READ_IIN
The MFR_READ_IIN command is a paged reading of the input current that applies the paged MFR_IIN_OFFSET
parameter. This calculation is similar to READ_IIN except the paged values are used.
MFR_READ_IIN = MFR_IIN_OFFSET + (IOUT • DUTYCYCLE)
This command has 2 data bytes and is formatted in Linear_5s_11s format.
READ_IOUT
The READ_IOUT command returns the average output current in amperes. The IOUT value is a function of:
a) the differential voltage measured across the ISENSE pins
b) the IOUT_CAL_GAIN value
c) the MFR_IOUT_CAL_GAIN_TC value, and
d) READ_TEMPERATURE_1 value
e) The MFR_TEMP_1_GAIN and the MFR_TEMP_1_OFFSET
This read-only command has two data bytes and is formatted in Linear_5s_11s format.
READ_TEMPERATURE_1
The READ_TEMPERATURE_1 command returns the temperature, in degrees Celsius, of the external sense element.
This read-only command has two data bytes and is formatted in Linear_5s_11s format.
READ_TEMPERATURE_2
The READ_TEMPERATURE_2 command returns the temperature, in degrees Celsius, of the internal sense element.
This read-only command has two data bytes and is formatted in Linear_5s_11s format.
PMBus
COMMAND DETAILS
LTC3880/LTC3880-1
100
3880fg
For more information www.linear.com/LTC3880
READ_DUTY_CYCLE
The READ_DUTY_CYCLE command returns the duty cycle of controller, in percent.
This read-only command has two data bytes and is formatted in Linear_5s_11s format.
READ_POUT
The READ_POUT command is a paged reading of the DC/DC converter output power in Watts. The POUT is calculated
based on the most recent correlated output voltage and current readings.
This command has 2 data bytes and is formatted in Linear_5s_11s format.
MFR_VOUT_PEAK
The MFR_VOUT_PEAK command reports the highest voltage, in volts, reported by the READ_VOUT measurement.
This command is cleared using the MFR_CLEAR_PEAKS command.
This read-only command has two data bytes and is formatted in Linear_16u format.
MFR_VIN_PEAK
The MFR_VIN_PEAK command reports the highest voltage, in volts, reported by the READ_VIN measurement.
This command is cleared using the MFR_CLEAR_PEAKS command.
This read-only command has two data bytes and is formatted in Linear_5s_11s format.
MFR_TEMPERATURE_1_PEAK
The MFR_TEMPERATURE_1_PEAK command reports the highest temperature, in degrees Celsius, reported by the
READ_TEMPERATURE_1 measurement.
This command is cleared using the MFR_CLEAR_PEAKS command.
This read-only command has two data bytes and is formatted in Linear_5s_11s format.
MFR_TEMPERATURE_2_PEAK
The MFR_TEMPERATURE_2_PEAK command reports the highest temperature, in degrees Celsius, reported by the
READ_TEMPERATURE_2 measurement.
This command is cleared using the MFR_CLEAR_PEAKS command.
This read-only command has two data bytes and is formatted in Linear_5s_11s format.
MFR_IOUT_PEAK
The MFR_IOUT_PEAK command reports the highest current, in amperes, reported by the READ_IOUT measurement.
This command is cleared using the MFR_CLEAR_PEAKS command.
This read-only command has two data bytes and is formatted in Linear_5s_11s format.
PMBus
COMMAND DETAILS
LTC3880/LTC3880-1
101
3880fg
For more information www.linear.com/LTC3880
NVM MEMORY COMMANDS
Store/Restore
COMMAND NAME
CMD
CODE DESCRIPTION TYPE PAGED FORMAT UNITS NVM
DEFAULT
VALUE
STORE_USER_ALL 0x15 Store user operating memory to EEPROM. Send Byte N NA
RESTORE_USER_ALL 0x16 Restore user operating memory from EEPROM. Send Byte N NA
MFR_COMPARE_USER_ALL 0xF0 Compares current command contents with NVM. Send Byte N NA
STORE_USER_ALL
The STORE_USER_ALL command instructs the PMBus device to copy the non-volatile user contents of the Operating
Memory to the matching locations in the non-volatile User NVM memory.
Executing this command if the die temperature exceeds 85°C is not recommended and the data retention of 10 years
cannot be guaranteed. If the die temperature exceeds 130°C, the STORE_USER_ALL command is disabled. The com-
mand is re-enabled when the IC temperature drops below 125°C.
Communication with the LTC3880 and programming of the NVM can be initiated when VDD33 is available and VIN
is not applied. To enable the part in this state, using global address 0x5B write 0x2B followed by 0xC4. The part
can now be communicated with, and the project file updated. To write the updated project file to the NVM issue a
STORE_USER_ALL command. When VIN is applied, a MFR_RESET must be issued to allow the PWM to be enabled
and valid ADCs to be read.
This write-only command has no data bytes.
RESTORE_USER_ALL
The RESTORE_USER_ALL command instructs the PMBus device to copy the contents of the non-volatile User memory
to the matching locations in the Operating Memory. The values in the Operating Memory are overwritten by the value
retrieved from the User commands. When a RESTORE_USER_ALL command is issued, the RUN pins and SHARE_CLK
pin are asserted low until the restore is complete. The RUN pins and SHARE_CLK pin are then released. The run pins
are held low for the MFR_RESTART_DELAY. The RESTORE_USER_ALL command will place the value of all commands
stored in NVM into the RAM ignoring the pin-strapped resistor configuration pins including ASEL. The MFR_RESET
command is recommended to be used instead of RESTORE_USER_ALL because the MFR_RESET command always
honors the ASEL pins and will honor the pin-strapped RCONFIG pins if the part is programmed to respect them.
RESTORE_USER_ALL. RESTORE_USER_ALL commands are disabled if the die exceeds 130°C and are not re-enabled
until the die temperature drops below 125°C.
This write-only command has no data bytes.
MFR_COMPARE_USER_ALL
The MFR_COMPARE_USER_ALL command instructs the PMBus device to compare current command contents with
what is stored in non-volatile memory. If the compare operation detects differences, a CML bit 0 fault will be generated.
This write-only command has no data bytes.
PMBus
COMMAND DETAILS
LTC3880/LTC3880-1
102
3880fg
For more information www.linear.com/LTC3880
Fault Log Operation
A conceptual diagram of the fault log is shown in Figure 32. The fault log provides telemetry recording capability to
the LTC3880. During normal operation, the contents of the status registers, the output voltage readings, temperature
readings as well as peak values of these quantities are stored in a continuously updated buffer in RAM. You can think
of the operation as being similar to a strip chart recorder. When a fault occurs, the contents are written into EEPROM
for nonvolatile storage. The EEPROM fault log is then locked. The part can be powered down with the fault log available
for reading at a later time. As a consequence of adding ECC, the area in the EEPROM available for fault log is reduced.
When reading the fault log from RAM, all 6 events of cyclical data remain. However, when the fault log is read from
EEPROM (after a reset), the last 2 events are lost. The read length of 147 bytes remains the same, but the fifth and
sixth events are a repeat of the fourth event.
3880 F32
TIME OF FAULT
TRANSFER TO
EEPROM AND
LOCK
AFTER FAULT
READ FROM
EEPROM AND
LOCK BUFFER
ADC READINGS
CONTINUOUSLY
FILL BUFFER
RAM EEPROM
8
•
•
•
•
•
•
Figure 32. Fault Log Conceptual Diagram
Fault Logging
COMMAND NAME CMD CODE DESCRIPTION TYPE PAGED
DATA
FORMAT UNITS NVM
DEFAULT
VALUE
MFR_FAULT_LOG 0xEE Fault log data bytes. This sequentially retrieved
data is used to assemble a complete fault log.
R Block N CF Y NA
MFR_FAULT_LOG_ STORE 0xEA Command a transfer of the fault log from RAM to
EEPROM. This causes the part to behave as if a
channel has faulted off.
Send Byte N NA
MFR_FAULT_LOG_CLEAR 0xEC Initialize the EEPROM block reserved for fault
logging and clear any previous fault logging
locks.
Send Byte N NA
PMBus
COMMAND DETAILS
LTC3880/LTC3880-1
103
3880fg
For more information www.linear.com/LTC3880
MFR_FAULT_LOG
The MFR_FAULT_LOG command allows the user to read the contents of the FAULT_LOG after the first fault occurrence
since the last MFR_FAULT_LOG_CLEAR command was last written. The contents of this command are stored in non-
volatile memory, and are cleared by the MFR_FAULT_LOG_CLEAR command. The length and content of this command
are listed in Table 11. If the user accesses the MFR_FAULT_LOG command and no fault log is present, the command
will return a data length of 0. If a fault log is present, the MFR_FAUTL_LOG will always return a block of data 147
bytes long. If a fault occurs within the first second of applying power, some of the earlier pages in the fault log may
not contain valid data.
NOTE: The approximate transfer time for this command is 3.4ms using a 400kHz clock.
This read-only command is in block format.
MFR_FAULT_LOG_STORE
The MFR_FAULT_LOG_STORE command forces the fault log operation to be written to NVM just as if a fault event
occurred. This command will generate a MFR_SPECIFIC fault if the “Enable Fault Logging” bit is set in the MFR_
CONFIG_ALL_LTC3880 command.
If the die temperature exceeds 130°C, the MFR_FAULT_LOG_STORE command is disabled until the IC temperature
drops below 125°C.
Up-Time Counter is in the Fault Log header. The counter is the time since the last reset in 200µs increments. This is
a 48-bit binary counter.
This write-only command has no data bytes.
PMBus
COMMAND DETAILS
LTC3880/LTC3880-1
104
3880fg
For more information www.linear.com/LTC3880
Table 11. Fault Logging
This table outlines the format of the block data from a read block data of the MFR_FAULT_LOG command.
Data Format Definitions LIN 11 = PMBus = Rev 1.1, Part 2, section 7.1
LIN 16 = PMBus Rev 1.1, Part 2, section 8. Mantissa portion only
BYTE = 8 bits interpreted per definition of this command
DATA BITS
DATA
FORMAT BYTE NUM BLOCK READ COMMAND
Block Length BYTE 147 The MFR_FAULT_LOG command is a fixed length of 147 bytes
The block length will be zero if a data log event has not been captured
HEADER INFORMATION
Position_Fault BYTE 0 Indicates the fault that caused the fault log to be activated.
MFR_REAL_TIME [7:0} BYTE 1 48-bit binary counter. The value is the time since the last reset in 200µs
increments.
[15:8} BYTE 2
[23:16] BYTE 3
[31:24] BYTE 4
[39:32] BYTE 5
[47:40] BYTE 6
MFR_VOUT_PEAK (PAGE 0) [15:8] LIN 16 7 Peak READ_VOUT page 0 since last MFR_CLEAR_PEAKS.
[7:0] LIN 16 8
MFR_VOUT_PEAK (PAGE 1) [15:8] LIN 16 9 Peak READ_VOUT page 1 since last MFR_CLEAR_PEAKS.
[7:0] LIN 16 10
MFR_IOUT_PEAK (PAGE 0) [15:8] LIN 11 11 Peak READ_IOUT page 0 since last MFR_CLEAR_PEAKS.
[7:0] LIN 11 12
MFR_IOUT_PEAK (PAGE 1) [15:8] LIN 11 13 Peak READ_IOUT page 1 since last MFR_CLEAR_PEAKS.
[7:0] LIN 11 14
MFR_VIN_PEAK [15:8] LIN 11 15 Peak READ_VIN since last MFR_CLEAR_PEAKS.
[7:0] LIN 11 16
READ_TEMPERATURE_1 (PAGE 0) [15:8] LIN 11 17 External temperature sensor 0 during last event
[7:0] LIN 11 18
READ_TEMPERATURE_1 (PAGE 1) [15:8] LIN 11 19 External temperature sensor 1 during last event
[7:0] LIN 11 20
READ_TEMPERATURE_2 [15:8] LIN 11 21 Internal temperature sensor during last event
[7:0] LIN 11 22
MFR_TEMPERATURE1_PEAK (PAGE 0) [15:8] LIN 11 23 Peak READ_TEMPERATURE_1 page 0 since MFR_CLEAR_PEAKS.
[7:0] LIN 11 24
MFR_TEMPERATURE1_PEAK (PAGE 1) [15:8] LIN 11 25 Peak READ_TEMPERATURE_1 page 1 since MFR_CLEAR_PEAKS.
[7:0] LIN 11 26
PMBus
COMMAND DETAILS
LTC3880/LTC3880-1
105
3880fg
For more information www.linear.com/LTC3880
CYCLICAL DATA
EVENT n
(Data at Which Fault Occurred; Most Recent Data)
Event “n” represents one complete cycle of ADC reads through the MUX
at time of fault. Example: If the fault occurs when the ADC is processing
step 15, it will continue to take readings through step 25 and then store
the header and all 6 event pages to EEPROM
READ_VOUT (PAGE 0) [15:8] LIN 16 27
[7:0] LIN 16 28
READ_VOUT (PAGE 1) [15:8] LIN 16 29
[7:0] LIN 16 30
READ_IOUT (PAGE 0) [15:8] LIN 11 31
[7:0] LIN 11 32
READ_IOUT (PAGE 1) [15:8] LIN 11 33
[7:0] LIN 11 34
READ_VIN [15:8] LIN 11 35
[7:0] LIN 11 36
READ_IIN [15:8] LIN 11 37
[7:0] LIN 11 38
STATUS_VOUT (PAGE 0) BYTE 39
STATUS_VOUT (PAGE 1) BYTE 40
STATUS_WORD (PAGE 0) [15:8] WORD 41
[7:0] WORD 42
STATUS_WORD (PAGE 1) [15:8] WORD 43
[7:0] WORD 44
STATUS_MFR_SPECIFIC (PAGE 0) BYTE 45
STATUS_MFR_SPECIFIC (PAGE 1) BYTE 46
EVENT n-1
(Data Measured Before Fault Was Detected)
READ_VOUT (PAGE 0) [15:8] LIN 16 47
[7:0] LIN 16 48
READ_VOUT (PAGE 1) [15:8] LIN 16 49
[7:0] LIN 16 50
READ_IOUT (PAGE 0) [15:8] LIN 11 51
[7:0] LIN 11 52
READ_IOUT (PAGE 1) [15:8] LIN 11 53
[7:0] LIN 11 54
READ_VIN [15:8] LIN 11 55
[7:0] LIN 11 56
READ_IIN [15:8] LIN 11 57
[7:0] LIN 11 58
STATUS_VOUT (PAGE 0) BYTE 59
STATUS_VOUT (PAGE 1) BYTE 60
STATUS_WORD (PAGE 0) [15:8] WORD 61
[7:0] WORD 62
STATUS_WORD (PAGE 1) [15:8] WORD 63
[7:0] WORD 64
STATUS_MFR_SPECIFIC (PAGE 0) BYTE 65
STATUS_MFR_SPECIFIC (PAGE 1) BYTE 66
*
*
*
PMBus
COMMAND DETAILS
LTC3880/LTC3880-1
106
3880fg
For more information www.linear.com/LTC3880
EVENT n-5
(Oldest Recorded Data)
READ_VOUT (PAGE 0) [15:8] LIN 16 127
[7:0] LIN 16 128
READ_VOUT (PAGE 1) [15:8] LIN 16 129
[7:0] LIN 16 130
READ_IOUT (PAGE 0) [15:8] LIN 11 131
[7:0] LIN 11 132
READ_IOUT (PAGE 1) [15:8] LIN 11 133
[7:0] LIN 11 134
READ_VIN [15:8] LIN 11 135
[7:0] LIN 11 136
READ_IIN [15:8] LIN 11 137
[7:0] LIN 11 138
STATUS_VOUT (PAGE 0) BYTE 139
STATUS_VOUT (PAGE 1) BYTE 140
STATUS_WORD (PAGE 0) [15:8] WORD 141
[7:0] WORD 142
STATUS_WORD (PAGE 1) [15:8] WORD 143
[7:0] WORD 144
STATUS_MFR_SPECIFIC (PAGE 0) BYTE 145
STATUS_MFR_SPECIFIC (PAGE 1) BYTE 146
PMBus
COMMAND DETAILS
LTC3880/LTC3880-1
107
3880fg
For more information www.linear.com/LTC3880
Table 11a: Explanation of Position_Fault Values
POSITION_FAULT VALUE SOURCE OF FAULT LOG
0xFF MFR_FAULT_LOG_STORE
0x00 TON_MAX_FAULT Channel 0
0x01 VOUT_OV_FAULT Channel 0
0x02 VOUT_UV_FAULT Channel 0
0x03 IOUT_OC_FAULT Channel 0
0x05 OT_FAULT Channel 0
0x06 UT_FAULT Channel 0
0x07 VIN_OV_FAULT Channel 0
0x0A MFR_OT_FAULT Channel 0
0x10 TON_MAX_FAULT Channel 1
0x11 VOUT_OV_FAULT Channel 1
0x12 VOUT_UV_FAULT Channel 1
0x13 IOUT_OC_FAULT Channel 1
0x15 OT_FAULT Channel 1
0x16 UT_FAULT Channel 1
0x17 VIN_OV_FAULT Channel 1
0x1A MFR_OT_FAULT Channel 1
MFR_FAULT_LOG_CLEAR
The MFR_FAULT_LOG_CLEAR command will erase the fault log file stored values. It will also clear bit 3 in the
STATUS_MFR_SPECIFIC command. After a clear is issued, the status can take up to 8ms to clear.
This write-only command is send bytes.
Block Memory Write/Read
COMMAND NAME CMD CODE DESCRIPTION TYPE PAGED
DATA
FORMAT UNITS NVM
DEFAULT
VALUE
MFR_EE_UNLOCK 0xBD Unlock user EEPROM for access by MFR_EE_ERASE and
MFR_EE_DATA commands.
R/W Byte N Reg NA
MFR_EE_ERASE 0xBE Initialize user EEPROM for bulk programming by MFR_EE_
DATA.
R/W Byte N Reg NA
MFR_EE_DATA 0xBF Data transferred to and from EEPROM using sequential
PMBus word reads or writes. Supports bulk programming.
R/W
Word
N Reg NA
All the NVM commands are disabled if the die temperature exceeds 130°C. NVM commands are re-enabled when the
die temperature drops below 125°C.
PMBus
COMMAND DETAILS
LTC3880/LTC3880-1
108
3880fg
For more information www.linear.com/LTC3880
MFR_EE_UNLOCK
Multiple writes to MFR_EE_UNLOCK with the appropriate unlock keys are used to enable MFR_EE_ERASE and MFR_
EE_DATA access and configure PEC.
Communication with the LTC3880 and programming of the NVM can be initiated when VDD33 is applied and VIN is
not. To enable the part in this state, use global address 0x5B command 0xBD data 0x2B followed by address 0x5B
command 0xBD data 0xC4. When VIN is applied, a MFR_RESET must be issued to allow the PWM to be enabled and
valid ADCs to be read.
Writing 0x2B followed by 0xD4 clears PEC, resets the EEPROM address pointer and unlocks the part for EEPROM
erase and data command writes.
Writing 0x2B followed by 0xD5 sets the PEC, resets the EEPROM address pointer and unlocks the part for EEPROM
erase and data command writes.
Writing 0x2B followed by 0x91 and 0xE4 clears PEC, resets the EEPROM address pointer and unlocks the part for
EEPROM data reads of all locations.
Writing 0x2B followed by 0x91 and 0xE5 sets PEC, resets the EEPROM address pointer and unlocks the part for
EEPROM data reads of all locations.
MFR_EE_ERASE
A single write after the appropriate unlock key erases the EEPROM allowing subsequent data writes. This register may
be read to indicate if an EEPROM access is in progress.
A value of 0x2B will erase the EEPROM. If the part is busy writing or erasing the EEPROM a non-zero value will be
returned.
MFR_EE_DATA
Sequential writes or reads perform block loads or restores from the EEPROM. Successive MFR_EE_DATA word writes
will enter the EEPROM until it is full. Extra writes will lock the part. The first write is to the lowest address. The first
read returns the 16 bit EEPROM packing revision ID. The second read returns the number of 16 bit words available.
Subsequent reads return EEPROM data starting with the lowest address.
PMBus
COMMAND DETAILS
LTC3880/LTC3880-1
109
3880fg
For more information www.linear.com/LTC3880
TYPICAL APPLICATIONS
High Efficiency Dual 500kHz 5V/3.3V Step-Down Converter with Sense Resistors
VIN
VDD33 VDD25
SGND
TG0
0.1µF
4.99k
0.1µF
1µF
1µF
L0, L1: VISHAY IHLP-2525CZ01 2.2µH
M1, M2: VISHAY Si4816BDY
1µF
4700pF
1000pF 1000pF
4700pF
22µF
V
IN
6V TO 24V
10µF
+
530µF
D2
10k
15.8k
VDD25
M1 M2
V
OUT1
5V
5A
4.99k 4.99k
L1
2.2µH 0.005Ω
L0
2.2µH
0.005Ω
D1
TG1
BG0
SYNC
10k
10k
23.2k
20k
11k
16.2k
20.5k
20k
12.7k
GPIO0
10k
GPIO1
10k
SDA
10k
SCL
10k
ALERT
10k
RUN0
FREQ_CFG
VOUT0_CFG
VOUT1_CFG
VTRIM0_CFG
VTRIM1_CFG
ASEL
10k
RUN1
WP
10k
100Ω
100Ω 100Ω
100Ω
SHARE_CLK
VDD33
BG1
PGND
BOOST0 BOOST1
SW0 SW1
INTVCC
LTC3880
TSNS0 TSNS1
ITHO ITH1
ISENSEO+ISENSE1+
VSENSEO+VSENSE1
VSENSEO–
ISENSEO–ISENSE1–
VOUT0
3.3V
5A
VOUT1
1.8V
15A
+
530µF
3880 TA03
220pF 220pF10nF 10nF
LTC3880/LTC3880-1
110
3880fg
For more information www.linear.com/LTC3880
TYPICAL APPLICATIONS
High Efficiency 350kHz 2-Phase 1.5V Dual Step-Down Converter with External VCC and Sense Resistors
VIN
VDD33 VDD25
SGND
TG0
0.1µF
4.99k
0.1µF
1µF
1µF1µF
4700pF
1000pF 1000pF
22µF
V
IN
6V TO 24V
10µF
+
530µF
D2
M2
M4
VDD25
M1
5VCC
M3
V
OUT1
1.5V
40A
2.55k
L1
0.42µH 0.0015Ω
L0
0.42µH
0.0015Ω
D1
TG1
BG0
SYNC
10k
24.9k
7.32k
20k
17.8k
GPIO0
10k
GPIO1
10k
SDA
SCL
10k
ALERT
10k
RUN0
FREQ_CFG
VOUT0_CFG
VOUT1_CFG
VTRIM0_CFG
VTRIM1_CFG
ASEL
RUN1
WP
10k
100Ω
100Ω 100Ω
100Ω
SHARE_CLK
VDD33
BG1
PGND
BOOST0 BOOST1
SW0 SW1
EXTVCC
LTC3880-1
TSNS0 TSNS1
ITHO ITH1
ISENSEO+ISENSE1+
VSENSEO+VSENSE1
VSENSEO–
ISENSEO–ISENSE1–
+
530µF
3880 TA04
220pF10nF 10nF
L0, L1: VITEC 59PR9875 0.42µH
M1, M2: INFINEON BSC050N03LS
M3, M4: INFINEON BSC010NE2LSI
LTC3880/LTC3880-1
111
3880fg
For more information www.linear.com/LTC3880
TYPICAL APPLICATIONS
High Efficiency 425kHz 1V Step-Down Dual Phase Converter with Power Blocks
VIN
GND
VIN
P1
PWMH
PWML
VGATE
VDD33 VDD25
SGND
TG0
4.99k
1µF10µF
1µF 1µF
1µF1µF
4700pF
0.22µF 0.22µF
1µF
22µF
V
IN
7V TO 13.2V
7V
GATE DRIVE
+
530µF
VDD25
V
OUT1
1.0V
60A
2.55k
TG1
BG0
SYNC
10k
24.9k
4.32k
20k
17.8k
16.2k
17.4k
GPIO0
10k
GPIO1
10k
SDA
SCL
10k
ALERT
10k
RUN0
FREQ_CFG
VOUT0_CFG
VOUT1_CFG
VTRIM0_CFG
VTRIM1_CFG
ASEL
RUN1
WP
10k
1.2k
SHARE_CLK
VDD33
BG1
PGND
BOOST0
VOUT
CS–
CS+
TEMP+
TEMP–
GND
VIN
P2
PWMH
PWML
VGATE
VOUT
CS–
CS+
TEMP+
TEMP–
BOOST1
SW0 SW1
INTVCC
LTC3880
TSNS0 TSNS1
ITHO ITH1
ISENSEO+ISENSE1+
VSENSEO+VSENSE1
VSENSEO–
ISENSEO–ISENSE1–
+
530µF
3880 TA05
220pF
P1, P2: VRA001-4C3G ACBEL POWER BLOCK
1µF
1.2k
LTC3880/LTC3880-1
112
3880fg
For more information www.linear.com/LTC3880
TYPICAL APPLICATIONS
High Efficiency 425kHz 3-Phase 1.8V and 1-Phase 2.5V Step-Down Converter
L0 TO L3: VISHAY IHLP-4040DZ-11 0.56µH, 1µH
M1, M2, M5, M6: INFINEON BSC050N03LS
M3, M4, M7, M8: INFINEON BSC010NE2LSI
VIN
SGND
TG0
0.1µF 0.1µF
1µF
0.22µF 0.22µF
4700pF
22µF
10µF
+
530µF
D2
M2
M4
24.9k
11.3k
VDD25
M1
M3
2.55k
1.58k
1µF 1µF
L1
0.56µH
L2
0.56µH
L3
1µH
L0
0.56µH
D1
TG1
BG0
SYNC
10k
1µF
1µF
1.58k 1.58k
15.8k
20k
17.8k
GPIO0
GPIO1
SDA
SCL
ALERT
RUN0
FREQ_CFG
VOUT0_CFG
VOUT1_CFG
VTRIM0_CFG
VTRIM1_CFG
ASEL
RUN1
WP
1.58k 1.58k
SHARE_CLK
VDD33
BG1
PGND
BOOST0 BOOST1
SW0 SW1
INTVCC
LTC3880
TSNS0 TSNS1
ITHO ITH1
ISENSEO+ISENSE1+
VSENSEO+VSENSE1
VSENSEO–
ISENSEO–ISENSE1–
V
OUT0
1.8V
75A
+
530µF
220pF
10nF
10nF
VIN
SGND
TG0
0.1µF 0.1µF
1µF
2200pF 2200pF
220pF
0.22µF
1µF
0.22µF
22µF
VIN
6V TO 24V
10µF
+
530µF
D4
M6
M8
24.9k
11.3k
VDD25
M5
M7
V
OUT1
2.5V
25A
4.99k 6.04k
1µF
D3
TG1
BG0
SYNC
20k
1µF
1µF
2k
15k
20k
15k
GPIO0
GPIO1
SDA
SCL
ALERT
RUN0
10k
FREQ_CFG
VOUT0_CFG
VOUT1_CFG
VTRIM0_CFG
VTRIM1_CFG
ASEL
RUN1
WP
1.58k
10k
10k
10k
10k
10k
5k
5k
4.99k
2k
SHARE_CLK
VDD33
BG1
PGND
BOOST0 BOOST1
SW0 SW1
INTVCC
LTC3880
TSNS0 TSNS1
ITHO ITH1
ISENSEO+ISENSE1+
VSENSEO+VSENSE1
VSENSEO–
ISENSEO–ISENSE1–
+
530µF
3880 TA06
220pF
10nF 10nF
LTC3880/LTC3880-1
113
3880fg
For more information www.linear.com/LTC3880
TYPICAL APPLICATIONS
High Efficiency 425kHz 4-Phase 1.0V Step-Down 1V Converter with an LTC3880 and LTC3870 PSM Slave
L0 TO L3: VISHAY IHLP-4040DZ-11 0.36µH
M1, M2, M5, M6: INFINEON BSC050N03LS
M3, M4, M7, M8: INFINEON BSC010NE2LSI
VIN
SGND
TG0
0.1µF 0.1µF
1µF
4700pF
220pF
0.22µF 0.22µF
22µF
10µF
+
530µF
D2
M2
M4
M1
M3
2.55k
1.58k
1µF
L1
0.36µH
L2
0.36µH
L3
0.36µH
L0
0.36µH
D1
TG1
BG0
SYNC 1µF
1µF
1.58k 1.58k
GPIO0
GPIO1
SDA
SCL
ALERT
RUN0
FREQ_CFG
VOUT0_CFG
VOUT1_CFG
VTRIM0_CFG
VTRIM1_CFG
ASEL
RUN1
WP
1.58k 1.58k
SHARE_CLK
VDD33
BG1
PGND
BOOST0 BOOST1
SW0 SW1
INTVCC
LTC3880
TSNS0 TSNS1
ITHO ITH1
ISENSEO+ISENSE1+
VSENSEO+VSENSE1
VSENSEO–
ISENSEO–ISENSE1–
+
530µF
10nF 10nF
VIN
SGND
TG0
0.1µF 0.1µF
1µF
220pF
0.22µF 0.22µF
22µF
VIN
6V TO 24V
10µF
+
530µF
D4
M6
M8
100k
FREQ
M5
M7
V
OUT1
1.0V
80A
1µF
1µF
D3
TG1
BG0
SYNC EXTVCC 1µF
1.58k
FAULT0
FAULT1
MODE0
MODE1
RUN0
10k
ILIM
PHASMD
RUN1
1.58k
10k
10k
10k
5k
5k
4.99k
1.58k
BG1
PGND
BOOST0 BOOST1
SW0 SW1
INTVCC
LTC3870
ITHO ITH1
ISENSEO+ISENSE1+
ISENSEO–ISENSE1–
+
530µF
3880 TA07
24.9k
4.32k
VDD25
20k
15k
20k
15k
LTC3880/LTC3880-1
114
3880fg
For more information www.linear.com/LTC3880
PACKAGE DESCRIPTION
6.00 ±0.10
(4 SIDES)
NOTE:
1. DRAWING IS A JEDEC PACKAGE OUTLINE VARIATION OF (WJJD-2)
2. DRAWING NOT TO SCALE
3. ALL DIMENSIONS ARE IN MILLIMETERS
4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE
MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.20mm ON ANY SIDE, IF PRESENT
5. EXPOSED PAD SHALL BE SOLDER PLATED
6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE TOP AND BOTTOM OF PACKAGE
PIN 1 TOP MARK
(SEE NOTE 6)
PIN 1 NOTCH
R = 0.45 OR
0.35 × 45°
CHAMFER
0.40 ±0.10
4039
1
2
BOTTOM VIEW—EXPOSED PAD
4.50 REF
(4-SIDES)
4.42 ±0.10
4.42 ±0.10
4.42 ±0.05
4.42 ±0.05
0.75 ±0.05 R = 0.115
TYP
0.25 ±0.05
0.50 BSC
0.200 REF
0.00 – 0.05
(UJ40) QFN REV Ø 0406
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED
0.70 ±0.05
4.50 ±0.05
(4 SIDES)
5.10 ±0.05
6.50 ±0.05
0.25 ±0.05
0.50 BSC
PACKAGE OUTLINE
R = 0.10
TYP
UJ Package
40-Lead Plastic QFN (6mm × 6mm)
(Reference LTC DWG # 05-08-1728 Rev Ø)
Please refer to http://www.linear.com/product/LTC3880#packaging for the most recent package drawings.
LTC3880/LTC3880-1
115
3880fg
For more information www.linear.com/LTC3880
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no representa-
tion that the interconnection of its circuits as described herein will not infringe on existing patent rights.
REVISION HISTORY
REV DATE DESCRIPTION PAGE NUMBER
A 10/11 Added I-grade, all sections updated 1-112
B 11/13 Amended upper limit of ISENSE0/1
Amended parametric errors and typical values
Amended Pin Function errors
Amended 2nd left paragraph under Operation
Amended 3rd left paragraph under Operation
Amended commands on Table 2
Amended formula on Figure 18a
Amended component on Figure 27
Amended Scratchpad table
Amended Identification table
Amended PMBus Command Details table
Amended components on Typical Application page
5
6
13
17
23
31
38
56
88
89
100
106
C 05/14 Added Initialization Time
Reduced readback time
Edit equations
Changed schematic MOSFET part numbers
Edit VOUT_MAX description
Edit MFR_VOUT_MAX description
Added STATUS Message content
5
Throughout
40, 57, 58
56, 106, 108,
109
31
33
90, 91, 92, 93
D 12/14 Added (PGOOD) after VOUT_UVUF 19, 24, 43,
65, 88
E 7/16 Added LTC3880-1 to VIN pin description
Added LTC3887/LTC3887-1 comparison table
14
1
F 9/16 Widened storage temperature range 4
G 04/17 Added ECC
Reduced initialization
Reduced conversion time
1, 16, 17, 24
5
6
LTC3880/LTC3880-1
116
3880fg
For more information www.linear.com/LTC3880
LINEAR TECHNOLOGY CORPORATION 2011
LT 0417 REV G • PRINTED IN USA
www.linear.com/LTC3880
RELATED PARTS
TYPICAL APPLICATION
High Efficiency Dual 425kHz 2.5V/1.8V Step-Down Converter
VIN
VDD33 VDD25
SGND
TG0
0.1µF
4.99k
0.1µF
1µF
1µF
L0, L1: VISHAY IHLP-4040DZ-11 1µH, 0.56µH
M1, M2: INFINEON BSC050N03LS
M3, M4: INFINEON BSC010NE2LS
1µF
2200pF
0.22µF 0.22µF
2200pF
22µF
V
IN
6V TO 24V
10µF
+
530µF
D2
M2
M4
20k
15k
VDD25
M1
M3
V
OUT1
1.8V
20A
6.04k 4.99k
2.0k
1µF
L1
0.56µH
L0
1.0µH
D1
TG1
BG0
SYNC
10k
24.9k
11.3k
10k
1µF
1.58k
15.8k
16.2k
17.4k
GPIO0
10k
GPIO1
10k
SDA
10k
SCL
10k
ALERT
10k
RUN0
FREQ_CFG
VOUT0_CFG
VOUT1_CFG
VTRIM0_CFG
VTRIM1_CFG
ASEL
10k
RUN1
WP
10k
2.0k 1.58k
SHARE_CLK
VDD33
BG1
PGND
BOOST0 BOOST1
SW0 SW1
INTVCC
LTC3880
TSNS0 TSNS1
ITHO ITH1
ISENSEO+ISENSE1+
VSENSEO+VSENSE1
VSENSEO–
ISENSEO–ISENSE1–
V
OUT0
2.5V
20A
VOUT1
1.8V
15A
+
530µF
3880 TA02
220pF 220pF10nF 10nF
PART NUMBER DESCRIPTION COMMENTS
LTM4676A Dual 13A or Single 26A Step-Down DC/DC µModule
Regulator with Digital Power System Management
VIN Up to 26.5V; 0.5V ≤ VOUT (±0.5%) ≤ 5.4V, ±2% IOUT ADC Accuracy, Fault
Logging, I2C/PMBus Interface, 16mm × 16mm × 5mm, BGA Package
LTM4675 Dual 9A or Single 18A Step-Down DC/DC μModule
Regulator with Digital Power System Management
4.5V ≤ VIN ≤17V; 0.5V ≤ VOUT ≤ 5.5V, ±0.5% VOUT Accuracy I2C/PMBus
Interface, 11.9mm × 16mm × 3.5mm, BGA Package
LTM4677 Dual 18A or Single 36A μModule Regulator with Digital
Power System Management
4.5V ≤ VIN ≤16V; 0.5V ≤ VOUT (±0.5%) ≤ 1.8V, I2C/PMBus Interface,
16mm × 16mm × 5mm, BGA Package
LTC3870/
LTC3870-1
Dual Output Multiphase Step-Down Slave Controller VIN Up to 60V, 0.5V ≤ VOUT ≤ 14V, Very High Output Current, Accurate Current
Sharing, Current Mode Applications
LTC3884 Dual Output MultiPhase Step-Down Controller with Sub
MilliOhm DCR Sensing Current Mode Control and Digital
Power System Management
4.5V ≤ VIN ≤ 38V, 0.5V ≤ VOUT (±0.5%) ≤ 5.5V, I2C/PMBus Interface,
Programmable Analog Loop Compensation, Input Current Sense
LTC3887 Dual Output Multiphase Step-Down DC/DC Controller
with Digital Power System Management
VIN Up to 24V, 0.5V ≤ VOUT0,1 ≤ 5.5V, 70mS Start-Up, Analog Control Loop,
I2C/PMBus Interface with EEPROM and 16-Bit ADC
LTC3886 60V Dual Output Step-Down Controller with Digital
Power System Management
4.5V ≤ VIN ≤ 60V, 0.5V ≤ VOUT0,1 (±0.5%) ≤ 13.8V,
I2C/PMBus Interface, Input Current Sense
LTC3883/
LTC3883-1
Single Phase Step-Down DC/DC Controller with Digital
Power System Management
VIN Up to 24V, 0.5V ≤ VOUT ≤ 5.5V, Input Current Sense Amplifier,
I2C/PMBus Interface with EEPROM and 16-Bit ADC
LTC3882/
LTC3882-1
Dual Output Multiphase Step-Down DC/DC Voltage
Mode Controller with Digital Power System Management
VIN Up to 38V, 0.5V ≤ VOUT1,2 ≤ 5.25V, ±0.5%, VOUT Accuracy I2C/PMBus
Interface with EEPROM and 16-Bit ADC
LTC3815 6A Monolithic Synchronous DC/DC Step-Down
Converter with Digital Power System Management
2.25V ≤ VIN ≤ 5.5V, 0.4V ≤ VOUT ≤ 0.72 VIN, Programmable VOUT Range
±25% with 0.1% Resolution, Up to 3MHz Operation with 13-Bit ADC
LTC3874 Multiphase Step-Down Synchronous Slave Controller for
Sub-MilliOhm DCR Sensing
4.5V ≤ VIN ≤ 38V, VOUT up to 5.5V, Very High Output Current, Accurate
Current Sharing, Current Mode Applications
This product has a license from PowerOne, Inc. related to digital power technology as set forth in U.S. Patent 7000125 and other related patents owned by PowerOne, Inc.
This license does not extend to standalone power supply products.