LT8606/LT8606B
1
Rev. D
For more information www.analog.com
FEATURES
TYPICAL APPLICATION
DESCRIPTION
42V, 350mA Synchronous
Step-Down Regulator with
2.5µA Quiescent Current
The LT
®
8606 is a compact, high efficiency, high speed
synchronous monolithic step-down switching regulator
that consumes only 1.7µA of non-switching quiescent
current. The LT8606 can deliver 350mA of continuous
current. Low ripple Burst Mode operation enables high
efficiency down to very low output currents while keeping
the output ripple below 10mVP-P. Internal compensation
with peak current mode topology allows the use of small
inductors and results in fast transient response and good
loop stability. The EN/UV pin has an accurate 1V threshold
and can be used to program VIN undervoltage lockout or
to shut down the LT8606. The PG pin signals when VOUT
is within ±8.5% of the programmed output voltage as well
as fault conditions.
The MSOP package includes a SYNC pin to synchronize
to an external clock, or to select Burst Mode operation
or pulse-skipping with or without spread-spectrum; the
TR/SS pin programs soft-start or tracking. The DFN pack-
age omits these pins and can be purchased in pulse-skip-
ping or Burst Mode operation variety.
APPLICATIONS
n Wide Input Voltage Range: 3.0V to 42V
n Ultralow Quiescent Current Burst Mode
®
Operation:
n <3µA IQ Regulating 12VIN to 3.3VOUT
n Output Ripple <10mVP-P
n High Efficiency 2MHz Synchronous Operation:
n >92% Efficiency at 0.35A, 12VIN to 5VOUT
n 350mA Maximum Continuous Output
n Fast Minimum Switch-On Time: 35ns
n Adjustable and Synchronizable: 200kHz to 2.2MHz
n Spread Spectrum Frequency Modulation for Low EMI
n Allows Use of Small Inductors
n Low Dropout
n Peak Current Mode Operation
n Accurate 1V Enable Pin Threshold
n Internal Compensation
n Output Soft-Start and Tracking
n Small Thermally Enhanced 10-Lead MSOP Package
or 8-Pin 2mm × 2mm DFN Package
n AEC-Q100 Qualified for Automotive Applications
n General Purpose Step-Down Converter
n Low EMI Step Down
All registered trademarks and trademarks are the property of their respective owners.
5V, 2MHz Step-Down
12VIN to 5VOUT Efficiency
VIN BST
EN/UV C1
0.1µF
C5
10pF
R2
1M
C2
1µF
VIN
5.5V TO 42V
C6
10nF
C3
1µF
VOUT
5V
350mA
POWER GOOD
R3
187k
8606 TA01a
L1
10µH
SYNC
INTVCC
TR/SS
RT
LT8606
GND
SW
PG
FB
R4
100k
R1
18.2k
L1 = XFL3010-103ME
C4
10µF
X7R
0805
fSW = 2MHz
f
SW
= 2MHz
L = 10µH
I
OUT
(mA)
0
50
50
55
60
65
70
75
80
85
90
95
EFFICIENCY (%)
8606 TA01b
PACKAGE SYNC FUNCTIONALITY
LT8606MSE MSE Programmable
LT8606DFN DFN Burst Mode Operation
LT8606BDFN DFN Pulse-Skipping Mode
Document Feedback
LT8606/LT8606B
2
Rev. D
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PIN CONFIGURATION
ABSOLUTE MAXIMUM RATINGS
VIN, EN/UV, PG ..........................................................42V
FB, TR/SS . .................................................................4V
SYNC Voltage . ............................................................6V
(Note 1)
1
2
3
4
5
BST
SW
INTVCC
RT
SYNC
10
9
8
7
6
EN/UV
VIN
PG
TR/SS
FB
TOP VIEW
11
GND
MSE PACKAGE
10-LEAD PLASTIC MSOP
θJA = 40°C/W
EXPOSED PAD (PIN 11) IS GND, MUST BE SOLDERED TO PCB
TOP VIEW
BST
SW
INTVCC
RT
EN/UV
VIN
PG
FB
DC PACKAGE
8-LEAD (2mm × 2mm) PLASTIC DFN
θJA = 102°C/W
EXPOSED PAD (PIN 9) IS GND, MUST BE SOLDERED TO PCB
9
GND
4
1
2
36
5
7
8
ORDER INFORMATION
LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE
LT8606EMSE#PBF LT8606EMSE#TRPBF LTGXT 10-Lead Plastic MSOP –40°C to 125°C
LT8606IMSE#PBF LT8606IMSE#TRPBF LTGXT 10-Lead Plastic MSOP –40°C to 125°C
LT8606HMSE#PBF LT8606HMSE#TRPBF LTGXT 10-Lead Plastic MSOP –40°C to 150°C
LT8606EDC#TRMPBF LT8606EDC#TRPBF LGXV 8-Lead Plastic 2mm × 2mm DFN –40°C to 125°C
LT8606IDC#TRMPBF LT8606IDC#TRPBF LGXV 8-Lead Plastic 2mm × 2mm DFN –40°C to 125°C
LT8606HDC#TRMPBF LT8606HDC#TRPBF LGXV 8-Lead Plastic 2mm × 2mm DFN –40°C to 150°C
LT8606BEDC#TRMPBF LT8606BEDC#TRPBF LGXW 8-Lead Plastic 2mm × 2mm DFN –40°C to 125°C
LT8606BIDC#TRMPBF LT8606BIDC#TRPBF LGXW 8-Lead Plastic 2mm × 2mm DFN –40°C to 125°C
LT8606BHDC#TRMPBF LT8606BHDC#TRPBF LGXW 8-Lead Plastic 2mm × 2mm DFN –40°C to 150°C
AUTOMOTIVE PRODUCTS**
LT8606EMSE#WPBF LT8606EMSE#WTRPBF LTGXT 10-Lead Plastic MSOP –40°C to 125°C
LT8606IMSE#WPBF LT8606IMSE#WTRPBF LTGXT 10-Lead Plastic MSOP –40°C to 125°C
LT8606JMSE#WPBF LT8606JMSE#WTRPBF LTGXT 10-Lead Plastic MSOP –40°C to 150°C
LT8606HMSE#WPBF LT8606HMSE#WTRPBF LTGXT 10-Lead Plastic MSOP –40°C to 150°C
LT8606EDC#WTRMPBF LT8606EDC#WTRPBF LGXV 8-Lead Plastic 2mm × 2mm DFN –40°C to 125°C
LT8606IDC#WTRMPBF LT8606IDC#WTRPBF LGXV 8-Lead Plastic 2mm × 2mm DFN –40°C to 125°C
LT8606JDC#WTRMPBF LT8606JDC#WTRPBF LGXV 8-Lead Plastic 2mm × 2mm DFN –40°C to 150°C
LT8606HDC#WTRMPBF LT8606HDC#WTRPBF LGXV 8-Lead Plastic 2mm × 2mm DFN –40°C to 150°C
Contact the factory for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container.
Tape and reel specifications. Some packages are available in 500 unit reels through designated sales channels with #TRMPBF suffix.
**Versions of this part are available with controlled manufacturing to support the quality and reliability requirements of automotive applications. These
models are designated with a #W suffix. Only the automotive grade products shown are available for use in automotive applications. Contact your
local Analog Devices account representative for specific product ordering information and to obtain the specific Automotive Reliability reports for
thesemodels.
Operating Junction Temperature Range (Note 2)
LT8606E ............................................ –40°C to 125°C
LT8606I ............................................. –40°C to 125°C
LT8606J ............................................ –40°C to 150°C
LT8606H ............................................ –40°C to 150°C
Storage Temperature Range .................. –65°C to 150°C
LT8606/LT8606B
3
Rev. D
For more information www.analog.com
The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C.
ELECTRICAL CHARACTERISTICS
PARAMETER CONDITIONS MIN TYP MAX UNITS
Minimum Input Voltage
l
2.5 3.0
3.2
V
VIN Quiescent Current VEN/UV = 0V
VEN/UV = 2V, Not Switching, VSYNC = 0V or LT8606 DFN, VIN ≤ 36V
l
1
1.7
5
12
µA
µA
VIN Current in Regulation VIN = 6V, VOUT = 2.7V, Output Load = 100µA
VIN = 6V, VOUT = 2.7V, Output Load = 1mA
l
l
56
500
90
700
µA
µA
Feedback Reference Voltage MSOP Package
VIN = 6V, ILOAD = 100mA
VIN = 6V, ILOAD = 100mA
l
0.774
0.762
0.778
0.778
0.782
0.798
V
V
DFN Package
VIN = 6V, ILOAD = 100mA
VIN = 6V, ILOAD = 100mA
l
0.771
0.753
0.778
0.778
0.785
0.803
V
V
Feedback Voltage Line Regulation VIN = 4.0V to 40V l±0.02 ±0.06 %/V
Feedback Pin Input Current VFB = 1V ±20 nA
Minimum On-Time ILOAD = 300mA, SYNC = 0V or LT8606 DFN
ILOAD = 300mA, SYNC = 1.9V or LT8606B DFN
l
l
35
35
65
60
ns
ns
Minimum Off Time ILOAD = 300mA l93 130 ns
Oscillator Frequency MSOP Package
RT = 221k, ILOAD = 250mA
RT = 60.4k, ILOAD = 250mA
RT = 18.2k, ILOAD = 250mA
l
l
l
155
640
1.90
200
700
2.00
245
760
2.10
kHz
kHz
MHz
DFN Package
RT = 221k, ILOAD = 250mA
RT = 60.4k, ILOAD = 250mA
RT = 18.2k, ILOAD = 250mA
l
l
l
140
610
1.85
200
700
2.00
260
790
2.15
kHz
kHz
MHz
Top Power NMOS On-Resistance ILOAD = 250mA 375 mΩ
Top Power NMOS Current Limit MSOP Package l0.65 0.9 1.15 A
DFN Package l0.65 1.1 1.4 A
Bottom Power NMOS On-Resistance 240 mΩ
SW Leakage Current VIN = 36V 5 µA
EN/UV Pin Threshold EN/UV Rising l0.99 1.05 1.11 V
EN/UV Pin Hysteresis 50 mV
EN/UV Pin Current VEN/UV = 2V ±20 nA
PG Upper Threshold Offset from VFB VFB Rising l5.0 8.5 13.0 %
PG Lower Threshold Offset from VFB VFB Falling l5.0 8.5 13.0 %
PG Hysteresis 0.5 %
PG Leakage VPG = 42V ±200 nA
PG Pull-Down Resistance VPG = 0.1V 550 1200 Ω
Sync Low Input Voltage MSOP Only l0.4 0.9 V
Sync High Input Voltage INTVCC = 3.5V, MSOP Only l2.7 3.2 V
TR/SS Source Current MSOP Only l1 2 3 µA
TR/SS Pull-Down Resistance Fault Condition, TR/SS = 0.1V, MSOP Only 300 900 Ω
Spread Spectrum Modulation Frequency VSYNC = 3.3V, MSOP Only 0.5 3 6 kHz
LT8606/LT8606B
4
Rev. D
For more information www.analog.com
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. Absolute Maximum Ratings are those values beyond
which the life of a device may be impaired.
Note 2: The LT8606E is guaranteed to meet performance specifications
from 0°C to 125°C junction temperature. Specifications over the –40°C
to 125°C operating junction temperature range are assured by design,
characterization, and correlation with statistical process controls. The
LT8606I is guaranteed over the full –40°C to 125°C operating junction
temperature range. The LT8606H is guaranteed over the full –40°C to
150°C operating junction temperature range. High junction temperatures
degrade operating lifetimes. Operating lifetime is derated at junction
temperatures greater than 125°C.
Note 3: This IC includes overtemperature protection that is intended to
protect the device during overload conditions. Junction temperature will
exceed 150°C when overtemperature protection is active. Continuous
operation above the specified maximum operating junction temperature
will reduce lifetime.
ELECTRICAL CHARACTERISTICS
FB Voltage Load Regulation
Efficiency (3.3V Output,
Burst Mode Operation)
TYPICAL PERFORMANCE CHARACTERISTICS
Efficiency (5V Output,
Burst Mode Operation)
Efficiency (5V Output,
Burst Mode Operation)
Efficiency (3.3V Output, Burst
Mode Operation)
I
OUT
(mA)
0
50
50
55
60
65
70
75
80
85
90
95
100
EFFICIENCY (%)
8606 G01
L = 10µH
fSW = 2MHz
SYNC = 0V OR LT8606 DFN
VIN = 12V
VIN = 24V
I
OUT
(mA)
0.001
0.01
0.1
1
10
0
10
20
30
40
50
60
70
80
90
EFFICIENCY (%)
8606 G02
VIN = 12V
VIN = 24V
L = 10µH
fSW = 2MHz
SYNC = 0V OR LT8606 DFN
I
OUT
(mA)
0
50
50
55
60
65
70
75
80
85
90
95
EFFICIENCY (%)
8606 G03
VIN = 12V
VIN = 24V
L = 6.8µH
fSW = 2MHz
SYNC = 0V OR LT8606 DFN
I
OUT
(mA)
0.001
0.01
0.1
1
10
0
10
20
30
40
50
60
70
80
90
100
EFFICIENCY (%)
8606 G04
VIN = 12V
VIN = 24V
L = 6.8µH
fSW = 2MHz
SYNC = 0V OR LT8606 DFN
TEMPERATURE (°C)
30
70
FB REGULATION VOLTAGE (mV)
8606 G05
OUTPUT CURRENT (mA)
0
50
–0.20
–0.15
–0.10
–0.05
0.00
0.05
0.10
0.15
0.20
CHANGE IN V
OUT
(%)
8606 G06
TA = 25°C, unless otherwise noted.
LT8606/LT8606B
5
Rev. D
For more information www.analog.com
TYPICAL PERFORMANCE CHARACTERISTICS
Line Regulation
No-Load Supply Current
(3.3V Output Switching)
No-Load Supply Current
vs Temperature (Not Switching)
Top FET Current Limit
vs Duty Cycle
Top FET Current Limit
vs Temperature
Switch Drop vs Temperature Switch Drop vs Switch Current
INPUT VOLTAGE (V)
2
10
18
26
34
42
–0.20
–0.15
–0.10
–0.05
0.00
0.05
0.10
0.15
0.20
CHANGE IN V
OUT
(%)
8606 G07
INPUT VOLTAGE (V)
2
10
18
26
34
42
2.00
2.25
2.50
2.75
3.00
3.25
3.50
3.75
4.00
4.25
4.50
I
IN
(µA)
8606 G08
L = 10µH
SYNC = 0V OR LT8606 DFN
TEMPERATURE (°C)
30
70
1.3
1.5
1.7
1.9
2.1
2.3
2.5
2.7
2.9
3.1
3.3
INPUT CURRENT (µA)
8606 G09
SYNC = 0V OR LT8606 DFN
DUTY CYCLE (%)
0
20
40
60
80
0.60
0.70
0.80
0.90
1.00
1.10
TOP FET CURRENT LIMIT (A)
8606 G10
DUTY CYCLE = 0
TEMPERATURE (°C)
30
70
0.90
0.95
1.00
1.05
1.10
TOP FET CURRENT LIMIT (A)
8606 G11
SWITCH CURRENT = 350mA
TEMPERATURE (°C)
10
30
50
70
90
0
50
SWITCH DROP (mV)
8606 G12
TOP SW
BOT SW
SWITCH CURRENT (mA)
0
50
0
25
50
75
SWITCH DROP (mV)
8606 G13
TOP SW
BOT SW
TA = 25°C, unless otherwise noted.
LT8606/LT8606B
6
Rev. D
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TYPICAL PERFORMANCE CHARACTERISTICS
TA = 25°C, unless otherwise noted.
Minimum On-Time
vs Temperature
Minimum Off-Time
vs Temperature
Dropout Voltage vs Output Current
Switching Frequency
vs Temperature
Burst Frequency vs Output Current
Minimum Load to Full Frequency
(SYNC Float to 1.9V)
(MSOP Package)
I
OUT
= 350mA
TEMPERATURE (°C)
10
30
50
70
90
30
31
32
33
34
35
36
37
38
39
40
MINIMUM ON–TIME (ns)
8606 G14
I
OUT
= 300mA
TEMPERATURE (°C)
10
30
50
70
90
80
85
90
95
MINIMUM OFF–TIME (ns)
8606 G15
L = XFL3010–682ME
0
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0
50
DROPOUT VOLTAGE (mV)
8606 G16
OUTPUT CURRENT (A)
R
T
= 18.2kΩ
TEMPERATURE (°C)
30
70
1975
1980
1985
1990
1995
2000
2005
2010
2015
2020
2025
SWITCHING FREQUENCY (kHz)
8606 G17
OUTPUT CURRENT (mA)
0
25
50
75
0
1000
1250
1500
1750
2000
2250
2500
SWITCHING FREQUENCY (kHz)
8606 G18
L = 6.8µH
VIN = 12V
VOUT = 3.3V
SYNC = 0V OR LT8606 DFN
L = 10µH
VIN = 12V
VOUT = 5V
RT = 18.2kΩ
INPUT VOLTAGE (V)
0
5
10
15
20
25
30
35
40
45
0
5
10
15
20
OUTPUT CURRENT (mA)
8606 G19
LT8606/LT8606B
7
Rev. D
For more information www.analog.com
TYPICAL PERFORMANCE CHARACTERISTICS
TA = 25°C, unless otherwise noted.
Frequency Foldback
Soft-Start Tracking
(MSOP Package)
Soft-Start Current vs Temperature
(MSOP Package) VIN UVLO
Start-Up Dropout Start-Up Dropout
FB VOLTAGE (V)
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
0
1000
1250
1500
1750
2000
2250
2500
FREQUENCY (kHz)
8606 G20
SYNC = 0V OR LT8606 DFN
RT = 18.2kΩ
SS VOLTAGE (V)
0
0.1
0.2
0.4
0.5
0.6
0.7
0.8
1.0
1.1
1.2
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
FB VOLTAGE (V)
8606 G21
TEMPERATURE (°C)
10
30
50
70
90
1.5
1.6
1.7
1.8
1.9
2.0
2.1
2.2
2.3
2.4
2.5
SOFT START CURRENT (µA)
8606 G22
TEMPERATURE (°C)
10
30
50
70
90
2.00
2.25
2.50
2.75
3.00
3.25
V
IN
UVLO (V)
8606 G23
R
LOAD
= 50Ω
INPUT VOLTAGE (V)
0
1
2
3
4
5
6
7
0
1
2
3
4
5
6
7
0
1
2
3
4
5
6
7
INPUT VOLTAGE (V)
OUTPUT VOLTAGE (V)
8606 G24
VIN
VOUT
R
LOAD
= 15Ω
INPUT VOLTAGE (V)
0
1
2
3
4
5
6
7
0
1
2
3
4
5
6
7
0
1
2
3
4
5
6
7
INPUT VOLTAGE (V)
OUTPUT VOLTAGE (V)
8606 G25
VIN
VOUT
LT8606/LT8606B
8
Rev. D
For more information www.analog.com
TYPICAL PERFORMANCE CHARACTERISTICS
Transient Response Transient Response
Switching Waveforms Switching Waveforms Switching Waveforms
200ns/DIV
VSW
5V/DIV
ILOAD
100mA/DIV
8606 G26
12VIN TO 5VOUT AT 250mA
2MHz
200ns/DIV
VSW
10V/DIV
ILOAD
100mA/DIV
8606 G27
36VIN TO 5VOUT AT 250mA
2MHz
2µs/DIV
SW
5V/DIV
ILOAD
100mA/DIV
VOUT
20mV/DIV
8606 G28
12VIN TO 5VOUT AT 5mA
10µF COUT
200µs/DIV
VOUT
100mV/DIV
ILOAD
100mA/DIV
8606 G29
VIN =12V, VOUT = 5V
25mA TO 275mA
COUT = 22µF
fSW = 2MHz
200µs/DIV
VOUT
100mV/DIV
ILOAD
100mA/DIV
8606 G30
VIN =12V, VOUT = 5V
100mA TO 350mA
COUT = 22µF
fSW = 2MHz
TA = 25°C, unless otherwise noted.
FREQUENCY (MHz)
AMPLITUDE (dBµV)
50
–5
40
25
15
5
30
45
35
20
10
0
–10
8606 G31
0500 900300 700 1000400 800200 600100
VERTICAL POLARIZATION
PEAK DETECTOR
CLASS 5 PEAK LIMIT
SPREAD SPECTRUM MODE
FIXED FREQUENCY
DC2564A DEMO BOARD
WITH EMI FILTER INSTALLED
14V INPUT TO 5V OUTPUT AT 350mA, fSW = 2MHz
Radiated EMI Performance
(CISPR25 Radiated Emission Test with Class 5 Peak Limits)
LT8606/LT8606B
9
Rev. D
For more information www.analog.com
PIN FUNCTIONS
BST: This pin is used to provide a drive voltage, higher
than the input voltage, to the topside power switch. Place
a 0.1µF boost capacitor as close as possible to the IC. Do
not place a resistor in series with this pin.
SW: The SW pin is the output of the internal power
switches. Connect this pin to the inductor and boost
capacitor. This node should be kept small on the PCB for
good performance.
INTVCC Internal 3.5V Regulator Bypass Pin. The internal
power drivers and control circuits are powered from this
voltage. INTVCC max output current is 20mA. Voltage
on INTVCC will vary between 2.8V and 3.5V. Decouple
this pin to power ground with at least a 1μF low ESR
ceramic capacitor. Do not load the INTVCC pin with exter-
nal circuitry.
RT: A resistor is tied between RT and ground to set the
switching frequency. When synchronizing, the R
T
resistor
should be chosen to set the LT8606 switching frequency
to equal or below the lowest synchronization input.
SYNC (MSOP Only): External Clock Synchronization Input.
Ground this pin for low ripple Burst Mode operation at low
output loads. Tie to a clock source for synchronization
to an external frequency. Leave floating for pulse-skip-
ping mode with no spread spectrum modulation. Tie to
INTV
CC
or tie to a voltage between 3.2V and 5.0V for
pulse-skipping mode with spread spectrum modulation.
When in pulse-skipping mode, the IQ regulating no load
will increase to several mA. There is no SYNC pin on the
LT8606 DFN package. The LT8606 DFN package internally
ties SYNC to ground. The LT8606B package internally
floats SYNC.
FB: The LT8606 regulates the FB pin to 0.778V. Connect
the feedback resistor divider tap to this pin.
TR/SS (MSOP Only): Output Tracking and Soft-Start Pin.
This pin allows user control of output voltage ramp rate
during start-up. A TR/SS voltage below 0.778V forces
the LT8606 to regulate the FB pin to equal the TR/SS pin
voltage. When TR/SS is above 0.778V, the tracking func-
tion is disabled and the internal reference resumes control
of the error amplifier. An internal 2μA pull-up current from
INTVCC on this pin allows a capacitor to program out-
put voltage slew rate. This pin is pulled to ground with a
300Ω MOSFET during shutdown and fault conditions; use
a series resistor if driving from a low impedance output.
There is no TR/SS pin on the LT8606 or LT8606B DFN
and the node is internally floated.
PG: The PG pin is the open-drain output of an internal
comparator. PG remains low until the FB pin is within
±8.5% of the final regulation voltage, and there are no
fault conditions. PG is valid when VIN is above 3.2V and
when EN/UV is high. PG is pulled low when VIN is above
3.2V and EN/UV is low. If VIN is near zero, PG will be high
impedance.
VIN: The VIN pin supplies current to the LT8606 internal
circuitry and to the internal topside power switch. This pin
must be locally bypassed. Be sure to place the positive
terminal of the input capacitor as close as possible to the
VIN pins, and the negative capacitor terminal as close as
possible to the GND pins.
EN/UV: The LT8606 is shut down when this pin is low
and active when this pin is high. The hysteretic threshold
voltage is 1.05V going up and 1.00V going down. Tie
to V
IN
if the shutdown feature is not used. An external
resistor divider from VIN can be used to program a VIN
threshold below which the LT8606 will shut down.
GND: Exposed Pad Pin. The exposed pad must be con-
nected to the negative terminal of the input capacitor
and soldered to the PCB in order to lower the thermal
resistance.
LT8606/LT8606B
10
Rev. D
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BLOCK DIAGRAM
+
+
–
+
–
SLOPE COMP
INTERNAL 0.778V REF
OSCILLATOR
200kHz TO 2.2MHz
BURST
DETECT
3.5V
REG
M1
M2
CBST
COUT
V
OUT
8606 BD
SW L
BST
SWITCH
LOGIC
AND
ANTI-
SHOOT
THROUGH
ERROR
AMP
SHDN
±8.5%
VC
SHDN
TSD
INTVCC UVLO
VIN UVLO
SHDN
TSD
VIN UVLO
EN/UV
1V +
–INTVCC
GND
PG
FB
R1
RPG
R2
RT
CSS
VOUT
CFF
TR/SS (MSOP ONLY)
2µA
RT
SYNC (MSOP ONLY)
VIN
VIN
CIN
CVCC
R3
OPT
R4
OPT
LT8606/LT8606B
11
Rev. D
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OPERATION
The LT8606 is a monolithic constant frequency current
mode step-down DC/DC converter. An oscillator with
frequency set using a resistor on the RT pin turns on
the internal top power switch at the beginning of each
clock cycle. Current in the inductor then increases until
the top switch current comparator trips and turns off the
top power switch. The peak inductor current at which the
top switch turns off is controlled by the voltage on the
internal VC node. The error amplifier servos the VC node
by comparing the voltage on the VFB pin with an inter-
nal 0.778V reference. When the load current increases
it causes a reduction in the feedback voltage relative to
the reference leading the error amplifier to raise the VC
voltage until the average inductor current matches the
new load current. When the top power switch turns off
the synchronous power switch turns on until the next
clock cycle begins or inductor current falls to zero. If over-
load conditions result in excess current flowing through
the bottom switch, the next clock cycle will be delayed
until switch current returns to a safe level.
If the EN/UV pin is low, the LT8606 is shut down and
draws 1µA from the input. When the EN/UV pin is above
1.05V, the switching regulator becomes active.
To optimize efficiency at light loads, the LT8606 enters
Burst Mode operation during light load situations.
Between bursts, all circuitry associated with controlling
the output switch is shut down, reducing the input supply
current to 1.7μA. In a typical application, 3.0μA will be
consumed from the input supply when regulating with no
load. The SYNC pin is tied low to use Burst Mode opera-
tion and can be floated to use pulse-skipping mode. If a
clock is applied to the SYNC pin the part will synchronize
to an external clock frequency and operate in pulse-skip-
ping mode. While in pulse-skipping mode the oscillator
operates continuously and positive SW transitions are
aligned to the clock. During light loads, switch pulses are
skipped to regulate the output and the quiescent current
will be several mA. The SYNC pin may be tied high for
spread spectrum modulation mode, and the LT8606 will
operate similar to pulse-skipping mode but vary the clock
frequency to reduce EMI. The LT8606 DFN has no SYNC
pin and will always operate in Burst Mode operation. The
LT8606B has no SYNC pin and will operate in pulse-skip-
ping mode.
Comparators monitoring the FB pin voltage will pull the PG
pin low if the output voltage varies more than ±8.5% (typ-
ical) from the set point, or if a fault condition is present.
The oscillator reduces the LT8606’s operating frequency
when the voltage at the FB pin is low and the part is in
Burst Mode operation. This frequency foldback helps to
control the inductor current when the output voltage is
lower than the programmed value which occurs during
start-up.
LT8606/LT8606B
12
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APPLICATIONS INFORMATION
Achieving Ultralow Quiescent Current
To enhance efficiency at light loads, the LT8606 enters
into low ripple Burst Mode operation, which keeps the
output capacitor charged to the desired output voltage
while minimizing the input quiescent current and mini-
mizing output voltage ripple. In Burst Mode operation the
LT8606 delivers single small pulses of current to the out-
put capacitor followed by sleep periods where the output
power is supplied by the output capacitor. While in sleep
mode the LT8606 consumes 1.7μA.
As the output load decreases, the frequency of single cur-
rent pulses decreases (see Figure1) and the percentage
of time the LT8606 is in sleep mode increases, result-
ing in much higher light load efficiency than for typical
converters. By maximizing the time between pulses, the
converter quiescent current approaches 3.0µA for a typ-
ical application when there is no output load. Therefore,
to optimize the quiescent current performance at light
loads, the current in the feedback resistor divider must
be minimized as it appears to the output as load current.
While in Burst Mode operation the current limit of the
top switch is approximately 150mA resulting in output
voltage ripple shown in Figure3. Increasing the output
capacitance will decrease the output ripple proportionally.
As load ramps upward from zero the switching frequency
will increase but only up to the switching frequency
programmed by the resistor at the RT pin as shown in
Table1. The output load at which the LT8606 reaches the
programmed frequency varies based on input voltage,
output voltage, and inductor choice.
For some applications it is desirable for the LT8606 to oper-
ate in pulse-skipping mode, offering two major differences
from Burst Mode operation. First is the clock stays awake at
all times and all switching cycles are aligned to the clock. In
this mode much of the internal circuitry is awake at all times,
increasing quiescent current to several hundred µA. Second
is that full switching frequency is reached at lower output
load than in Burst Mode operation as shown in Figure2. Full
Switching Frequency Minimum Load vs VIN in Pulse Skipping
Mode (MSOP ONLY). To enable pulse-skipping mode the
SYNC pin is floated. To achieve spread spectrum modula-
tion with pulse-skipping mode, the SYNC pin is tied high.
Figure2. Full Switching Frequency Minimum Load vs VIN in
Pulse Skipping Mode (MSOP ONLY)
Figure3. Burst Mode Operation
Figure1. SW Burst Mode Frequency vs Output Current
0
25
50
75
0
1000
1250
1500
1750
2000
2250
2500
SWITCHING FREQUENCY (kHz)
8606 F01
L = 6.8µH
VIN = 12V
VOUT = 3.3V
SYNC = 0V
OUTPUT CURRENT (mA)
INPUT VOLTAGE (V)
0
5
10
15
20
25
30
35
40
45
0
5
10
15
20
OUTPUT CURRENT (mA)
8606 F02
L = 10µH
VIN = 12V
VOUT = 5V
RT = 18.2kΩ
2µs/DIV
SW
5V/DIV
ILOAD
100mA/DIV
VOUT
20mV/DIV
8606 F03
While a clock is applied to the SYNC pin the LT8606 will also
operate in pulse-skipping mode. The LT8606 DFN is always
programmed for Burst Mode operation and cannot enter
pulse-skipping mode. The LT8606B DFN is programmed for
pulse-skipping mode and cannot enter Burst Mode operation.
LT8606/LT8606B
13
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APPLICATIONS INFORMATION
FB Resistor Network
The output voltage is programmed with a resistor divider
between the output and the FB pin. Choose the resistor
values according to:
R1=R2
V
OUT
0.778V –1
⎛
⎝
⎜⎞
⎠
⎟
1% resistors are recommended to maintain output voltage
accuracy.
The total resistance of the FB resistor divider should be
selected to be as large as possible when good low load
efficiency is desired: The resistor divider generates a
small load on the output, which should be minimized to
optimize the quiescent current at low loads.
When using large FB resistors, a 10pF phase lead capac-
itor should be connected from VOUT to FB.
Setting the Switching Frequency
The LT8606 uses a constant frequency PWM architec-
ture that can be programmed to switch from 200kHz
to 2.2MHz by using a resistor tied from the RT pin to
ground. A table showing the necessary R
T
value for a
desired switching frequency is in Table1. When in spread
spectrum modulation mode, the frequency is modulated
upwards of the frequency set by RT.
Table1. SW Frequency vs RT Value
fSW (MHz) RT (kΩ)
0.2 221
0.300 143
0.400 110
0.500 86.6
0.600 71.5
0.700 60.4
0.800 52.3
0.900 46.4
1.000 40.2
1.200 33.2
1.400 27.4
1.600 23.7
1.800 20.5
2.000 18.2
2.200 16.2
Operating Frequency Selection and Trade-Offs
Selection of the operating frequency is a trade-off between
efficiency, component size, and input voltage range. The
advantage of high frequency operation is that smaller
inductor and capacitor values may be used. The disad-
vantages are lower efficiency and a smaller input voltage
range.
The highest switching frequency (fSW(MAX)) for a given
application can be calculated as follows:
fSW(MAX) =VOUT +VSW(BOT)
tON(MIN) VIN – VSW(TOP) +VSW(BOT)
( )
where VIN is the typical input voltage, VOUT is the output
voltage, V
SW(TOP)
and V
SW(BOT)
are the internal switch
drops (~0.13V, ~0.06V, respectively at max load) and
t
ON(MIN)
is the minimum top switch on-time (see Electrical
Characteristics). This equation shows that slower switch-
ing frequency is necessary to accommodate a high VIN/
VOUT ratio.
For transient operation V
IN
may go as high as the Abs Max
rating regardless of the R
T
value, however the LT8606
will reduce switching frequency as necessary to maintain
control of inductor current to assure safe operation.
The LT8606 is capable of maximum duty cycle approach-
ing 100%, and the VIN to VOUT dropout is limited by the
RDS(ON) of the top switch. In this mode the LT8606 skips
switch cycles, resulting in a lower switching frequency
than programmed by RT.
For applications that cannot allow deviation from the pro-
grammed switching frequency at low VIN/VOUT ratios use
the following formula to set switching frequency:
VIN(MIN) =VOUT +VSW(BOT)
1– fSW • tOFF(MIN)
– VSW(BOT) +VSW(TOP)
where VIN(MIN) is the minimum input voltage without
skipped cycles, VOUT is the output voltage, VSW(TOP) and
VSW(BOT) are the internal switch drops (~0.13V, ~0.06V,
respectively at max load), fSW is the switching frequency
(set by RT), and tOFF(MIN) is the minimum switch off-
time. Note that higher switching frequency will increase
the minimum input voltage below which cycles will be
dropped to achieve higher duty cycle.
LT8606/LT8606B
14
Rev. D
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APPLICATIONS INFORMATION
Inductor Selection and Maximum Output Current
The LT8606 is designed to minimize solution size by
allowing the inductor to be chosen based on the output
load requirements of the application. During overload or
short circuit conditions the LT8606 safely tolerates oper-
ation with a saturated inductor through the use of a high
speed peak-current mode architecture.
A good first choice for the inductor value is:
L=
V
OUT
+V
SW(BOT)
f
SW
• 4
where f
SW
is the switching frequency in MHz, V
OUT
is
the output voltage, VSW(BOT) is the bottom switch drop
(~0.06V) and L is the inductor value in μH.
To avoid overheating and poor efficiency, an inductor
must be chosen with an RMS current rating that is greater
than the maximum expected output load of the applica-
tion. In addition, the saturation current (typically labeled
ISAT) rating of the inductor must be higher than the load
current plus 1/2 of in inductor ripple current:
IL(PEAK) =ILOAD(MAX) +
1
2
ΔL
where ∆I
L
is the inductor ripple current as calculated sev-
eral paragraphs below and I
LOAD(MAX)
is the maximum
output load for a given application.
As a quick example, an application requiring 0.25A output
should use an inductor with an RMS rating of greater
than 0.5A and an ISAT of greater than 0.7A. To keep the
efficiency high, the series resistance (DCR) should be less
than 0.04Ω, and the core material should be intended for
high frequency applications.
The LT8606 limits the peak switch current in order to
protect the switches and the system from overload faults.
The top switch current limit (ILIM) is at least 0.65A at
low duty cycles and decreases linearly to at least 0.5A
at D=0.8. The inductor value must then be sufficient to
supply the desired maximum output current (IOUT(MAX)),
which is a function of the switch current limit (ILIM) and
the ripple current:
IOUT(MAX) =ILIM –
ΔI
L
2
The peak-to-peak ripple current in the inductor can be
calculated as follows:
ΔIL=VOUT
L • fSW
1– VOUT
VIN(MAX)
⎛
⎝
⎜⎞
⎠
⎟
where fSW is the switching frequency of the LT8606, and
L is the value of the inductor. Therefore, the maximum
output current that the LT8606 will deliver depends on
the switch current limit, the inductor value, and the input
and output voltages. The inductor value may have to be
increased if the inductor ripple current does not allow
sufficient maximum output current (IOUT(MAX)) given the
switching frequency, and maximum input voltage used in
the desired application.
The optimum inductor for a given application may differ
from the one indicated by this design guide. A larger value
inductor provides a higher maximum load current and
reduces the output voltage ripple. For applications requir-
ing smaller load currents, the value of the inductor may
be lower and the LT8606 may operate with higher ripple
current. This allows use of a physically smaller inductor,
or one with a lower DCR resulting in higher efficiency. Be
aware that low inductance may result in discontinuous
mode operation, which further reduces maximum load
current.
For more information about maximum output current and
discontinuous operation, see Analog Devices Application
Note 44.
Finally, for duty cycles greater than 50% (VOUT/VIN > 0.5),
a minimum inductance is required to avoid sub-harmonic
oscillation. See Analog Devices Application Note 19.
Input Capacitor
Bypass the input of the LT8606 circuit with a ceramic
capacitor of X7R or X5R type. Y5V types have poor perfor-
mance over temperature and applied voltage, and should
not be used. A 4.7μF to 10μF ceramic capacitor is ade-
quate to bypass the LT8606 and will easily handle the rip-
ple current. Note that larger input capacitance is required
when a lower switching frequency is used. If the input
power source has high impedance, or there is significant
LT8606/LT8606B
15
Rev. D
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APPLICATIONS INFORMATION
inductance due to long wires or cables, additional bulk
capacitance may be necessary. This can be provided with
a low performance electrolytic capacitor.
Step-down regulators draw current from the input sup-
ply in pulses with very fast rise and fall times. The input
capacitor is required to reduce the resulting voltage rip-
ple at the LT8606 and to force this very high frequency
switching current into a tight local loop, minimizing EMI.
A 4.7μF capacitor is capable of this task, but only if it is
placed close to the LT8606 (see the PCB Layout section).
A second precaution regarding the ceramic input capac-
itor concerns the maximum input voltage rating of the
LT8606. A ceramic input capacitor combined with trace
or cable inductance forms a high quality (under damped)
tank circuit. If the LT8606 circuit is plugged into a live
supply, the input voltage can ring to twice its nominal
value, possibly exceeding the LT8606’s voltage rating.
This situation is easily avoided (see Analog Devices
Application Note 88).
Output Capacitor and Output Ripple
The output capacitor has two essential functions. Along
with the inductor, it filters the square wave generated
by the LT8606 to produce the DC output. In this role it
determines the output ripple, thus low impedance at the
switching frequency is important. The second function is
to store energy in order to satisfy transient loads and sta-
bilize the LT8606’s control loop. Ceramic capacitors have
very low equivalent series resistance (ESR) and provide
the best ripple performance. A good starting value is:
COUT =
100
V
OUT
• f
SW
where fSW is in MHz, and COUT is the recommended
output capacitance in μF. Use X5R or X7R types. This
choice will provide low output ripple and good tran-
sient response. Transient performance can be improved
with a higher value output capacitor and the addition of
a feedforward capacitor placed between VOUT and FB.
Increasing the output capacitance will also decrease the
output voltage ripple. A lower value of output capacitor
can be used to save space and cost but transient per-
formance will suffer and may cause loop instability. See
the Typical Applications in this data sheet for suggested
capacitor values.
When choosing a capacitor, special attention should be
given to the data sheet to calculate the effective capaci-
tance under the relevant operating conditions of voltage
bias and temperature. A physically larger capacitor or one
with a higher voltage rating may be required.
Ceramic Capacitors
Ceramic capacitors are small, robust and have very low
ESR. However, ceramic capacitors can cause problems
when used with the LT8606 due to their piezoelectric
nature. When in Burst Mode operation, the LT8606’s
switching frequency depends on the load current, and at
very light loads the LT8606 can excite the ceramic capacitor
at audio frequencies, generating audible noise. Since the
LT8606 operates at a lower current limit during Burst Mode
operation, the noise is typically very quiet to a casual ear.
If this is unacceptable, use a high performance tantalum
or electrolytic capacitor at the output.
A final precaution regarding ceramic capacitors concerns
the maximum input voltage rating of the LT8606. As pre-
viously mentioned, a ceramic input capacitor combined
with trace or cable inductance forms a high quality (under
damped) tank circuit. If the LT8606 circuit is plugged into
a live supply, the input voltage can ring to twice its nom-
inal value, possibly exceeding the LT8606’s rating. This
situation is easily avoided (see Analog Devices Application
Note 88).
Enable Pin
The LT8606 is in shutdown when the EN pin is low and
active when the pin is high. The rising threshold of the EN
comparator is 1.05V, with 50mV of hysteresis. The EN pin
can be tied to VIN if the shutdown feature is not used, or
tied to a logic level if shutdown control is required.
Adding a resistor divider from V
IN
to EN programs the
LT8606 to regulate the output only when VIN is above
a desired voltage (see Block Diagram). Typically, this
threshold, VIN(EN), is used in situations where the input
LT8606/LT8606B
16
Rev. D
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supply is current limited, or has a relatively high source
resistance. A switching regulator draws constant power
from the source, so source current increases as source
voltage drops. This looks like a negative resistance load
to the source and can cause the source to current limit or
latch low under low source voltage conditions. The V
IN(EN)
threshold prevents the regulator from operating at source
voltages where the problems might occur. This threshold
can be adjusted by setting the values R3 and R4 such that
they satisfy the following equation:
VIN(EN) =
R3
R4 +1
⎛
⎝
⎜⎞
⎠
⎟•1V
where the LT8606 will remain off until VIN is above VIN(EN).
Due to the comparator’s hysteresis, switching will not
stop until the input falls slightly below VIN(EN).
When in Burst Mode operation for light-load currents, the
current through the VIN(EN) resistor network can easily be
greater than the supply current consumed by the LT8606.
Therefore, the VIN(EN) resistors should be large to mini-
mize their effect on efficiency at low loads.
INTVCC Regulator
An internal low dropout (LDO) regulator produces the 3.5V
supply from VIN that powers the drivers and the internal
bias circuitry. The INTVCC can supply enough current for
the LT8606’s circuitry and must be bypassed to ground
with a minimum of 1μF ceramic capacitor. Good bypass-
ing is necessary to supply the high transient currents
required by the power MOSFET gate drivers. Applications
with high input voltage and high switching frequency will
increase die temperature because of the higher power
dissipation across the LDO. Do not connect an external
load to the INTVCC pin.
Output Voltage Tracking and Soft-Start (MSOP ONLY)
The LT8606 allows the user to program its output voltage
ramp rate by means of the TR/SS pin. An internal 2μA
pulls up the TR/SS pin to INTVCC. Putting an external
capacitor on TR/SS enables soft-starting the output to
prevent current surge on the input supply. During the soft-
start ramp the output voltage will proportionally track the
APPLICATIONS INFORMATION
TR/SS pin voltage. For output tracking applications, TR/
SS can be externally driven by another voltage source.
From 0V to 0.778V, the TR/SS voltage will override the
internal 0.778V reference input to the error amplifier, thus
regulating the FB pin voltage to that of TR/SS pin. When
TR/SS is above 0.778V, tracking is disabled and the feed-
back voltage will regulate to the internal reference voltage.
An active pull-down circuit is connected to the TR/SS pin
which will discharge the external soft-start capacitor in
the case of fault conditions and restart the ramp when the
faults are cleared. Fault conditions that clear the soft-start
capacitor are the EN/UV pin transitioning low, VIN voltage
falling too low, or thermal shutdown. The LT8606 and
LT8606B DFN does not have TR/SS pin or functionality.
Output Power Good
When the LT8606’s output voltage is within the ±8.5%
window of the regulation point, which is a VFB voltage in
the range of 0.716V to 0.849V (typical), the output voltage
is considered good and the open-drain PG pin goes high
impedance and is typically pulled high with an external
resistor. Otherwise, the internal drain pull-down device
will pull the PG pin low. To prevent glitching both the
upper and lower thresholds include 0.5% of hysteresis.
The PG pin is also actively pulled low during several fault
conditions: EN/UV pin is below 1V, INTVCC has fallen too
low, VIN is too low, or thermal shutdown.
Synchronization (MSOP ONLY)
To select low ripple Burst Mode operation, tie the SYNC
pin below 0.4V (this can be ground or a logic low out-
put). To synchronize the LT8606 oscillator to an external
frequency connect a square wave (with 20% to 80% duty
cycle) to the SYNC pin. The square wave amplitude should
have valleys that are below 0.9V and peaks above 2.7V
(up to 5V).
The LT8606 will not enter Burst Mode operation at low
output loads while synchronized to an external clock, but
instead will pulse skip to maintain regulation. The LT8606
may be synchronized over a 200kHz to 2.2MHz range. The
RT resistor should be chosen to set the LT8606 switching
frequency equal to or below the lowest synchronization
LT8606/LT8606B
17
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APPLICATIONS INFORMATION
input. For example, if the synchronization signal will be
500kHz and higher, the R
T
should be selected for 500kHz.
The slope compensation is set by the RT value, while the
minimum slope compensation required to avoid subhar-
monic oscillations is established by the inductor size,
input voltage, and output voltage. Since the synchroniza-
tion frequency will not change the slopes of the inductor
current waveform, if the inductor is large enough to avoid
subharmonic oscillations at the frequency set by R
T
, then
the slope compensation will be sufficient for all synchro-
nization frequencies.
For some applications it is desirable for the LT8606 to
operate in pulse-skipping mode, offering two major differ-
ences from Burst Mode operation. First is the clock stays
awake at all times and all switching cycles are aligned
to the clock. Second is that full switching frequency is
reached at lower output load than in Burst Mode operation
as shown in Figure2. Full Switching Frequency Minimum
Load vs VIN in Pulse Skipping Mode (MSOP ONLY) in an
earlier section. These two differences come at the expense
of increased quiescent current. To enable pulse-skipping
mode the SYNC pin is floated.
For some applications, reduced EMI operation may be
desirable, which can be achieved through spread spec-
trum modulation. This mode operates similar to pulse
skipping mode operation, with the key difference that the
switching frequency is modulated up and down by a 3kHz
triangle wave. The modulation has the frequency set by R
T
as the low frequency, and modulates up to approximately
20% higher than the frequency set by RT. To enable spread
spectrum mode, tie SYNC to INTVCC or drive to a voltage
between 3.2V and 5V.
The LT8606 does not operate in forced continuous mode
regardless of SYNC signal. The LT8606 DFN is always
programmed for Burst Mode operation and cannot enter
pulse-skipping mode. The LT8606B DFN is programmed
for pulse-skipping mode and cannot enter Burst Mode
operation.
Shorted and Reversed Input Protection
The LT8606 will tolerate a shorted output. Several features
are used for protection during output short-circuit and
brownout conditions. The first is the switching frequency
will be folded back while the output is lower than the set
point to maintain inductor current control. Second, the
bottom switch current is monitored such that if inductor
current is beyond safe levels switching of the top switch
will be delayed until such time as the inductor current
falls to safe levels. This allows for tailoring the LT8606
to individual applications and limiting thermal dissipation
during short circuit conditions.
Frequency foldback behavior depends on the state of the
SYNC pin: If the SYNC pin is low, the switching frequency
will slow while the output voltage is lower than the pro-
grammed level. If the SYNC pin is connected to a clock
source, tied high or floated, the LT8606 will stay at the
programmed frequency without foldback and only slow
switching if the inductor current exceeds safe levels.
There is another situation to consider in systems where
the output will be held high when the input to the LT8606
is absent. This may occur in battery charging applications
or in battery backup systems where a battery or some
other supply is diode ORed with the LT8606’s output.
If the VIN pin is allowed to float and the EN pin is held
high (either by a logic signal or because it is tied to VIN),
then the LT8606’s internal circuitry will pull its quiescent
current through its SW pin. This is acceptable if the sys-
tem can tolerate several μA in this state. If the EN pin is
grounded the SW pin current will drop to near 0.7µA.
However, if the V
IN
pin is grounded while the output is
held high, regardless of EN, parasitic body diodes inside
the LT8606 can pull current from the output through the
SW pin and the VIN pin. Figure4 shows a connection of
the VIN and EN/UV pins that will allow the LT8606 to run
only when the input voltage is present and that protects
against a shorted or reversed input.
VIN
VIN
LT8606
GND
D1
8606 F04
EN/UV
Figure4. Reverse VIN Protection
LT8606/LT8606B
18
Rev. D
For more information www.analog.com
APPLICATIONS INFORMATION
the ground plane as much as possible, and add thermal
vias under and near the LT8606 to additional ground
planes within the circuit board and on the bottom side.
Thermal Considerations
For higher ambient temperatures, care should be taken in
the layout of the PCB to ensure good heat sinking of the
LT8606. Figure5 shows the recommended component
placement with trace, ground plane and via locations.
The exposed pad on the bottom of the package must be
soldered to a ground plane. This ground should be tied
to large copper layers below with thermal vias; these lay-
ers will spread heat dissipated by the LT8606. Placing
additional vias can reduce thermal resistance further. The
maximum load current should be derated as the ambient
temperature approaches the maximum junction rating.
Power dissipation within the LT8606 can be estimated
by calculating the total power loss from an efficiency
measurement and subtracting the inductor loss. The
die temperature is calculated by multiplying the LT8606
power dissipation by the thermal resistance from junction
to ambient. The LT8606 will stop switching and indicate
a fault condition if safe junction temperature is exceeded.
PCB Layout
For proper operation and minimum EMI, care must be
taken during printed circuit board layout. Note that large,
switched currents flow in the LT8606’s VIN pins, GND
pins, and the input capacitor (CIN). The loop formed
by the input capacitor should be as small as possible
by placing the capacitor adjacent to the VIN and GND
pins. When using a physically large input capacitor the
resulting loop may become too large in which case using
a small case/value capacitor placed close to the VIN and
GND pins plus a larger capacitor further away is pre-
ferred. These components, along with the inductor and
output capacitor, should be placed on the same side of
the circuit board, and their connections should be made
on that layer. Place a local, unbroken ground plane under
the application circuit on the layer closest to the surface
layer. The SW and BOOST nodes should be as small as
possible. Finally, keep the FB and RT nodes small so
that the ground traces will shield them from the SW and
BOOST nodes. The exposed pad on the bottom of the
package must be soldered to ground so that the pad is
connected to ground electrically and also acts as a heat
sink thermally. To keep thermal resistance low, extend
Figure5. PCB Layout
8606 F05
GND VIA VIN VIA VOUT VIA EN/UV VIA OTHER SIGNAL VIA
COUT
CIN
CBST
CVCC
GROUND PLANE ON LAYER 2
RT
L
CIN(OPT)
R1
CFF R2
R4
R3
RPG
1
CSS
LT8606/LT8606B
19
Rev. D
For more information www.analog.com
TYPICAL APPLICATIONS
VIN BST
EN/UV C1
0.1µF
C5
10pF
R2
1M
VIN
5.5V TO 42V
C6
10nF
C3
1µF
VOUT
5V
350mA
POWER GOOD
R3
187k
8606 TA02
L1
10µH
SYNC
INTVCC
TR/SS
RT
LT8606
GND
SW
PG
FB
R4
100k
R1
18.2k
L1 = XFL3010-103ME
C4
10µF
X7R
0805
fSW = 2MHz
C2
1µF
X7R
0805
VIN BST
EN/UV C1
0.1µF
C5
10pF
R2
1M
VIN
3.8V TO 42V
C6
10nF
C3
1µF
VOUT
3.3V
350mA
POWER GOOD
R3
309k
8606 TA03
L1
6.8µH
SYNC
INTVCC
TR/SS
RT
LT8606
GND
SW
PG
FB
R4
100k
R1
18.2k
L1 = XFL3010-682ME
C4
10µF
X7R
0805
fSW = 2MHz
C2
1µF
X7R
0805
VIN BST
EN/UV C1
0.1µF
C5
100pF
R2
1M
VIN
12.7V TO 42V
C6
10nF
C3
1µF
VOUT
12V
350mA
POWER GOOD
R3
69.8k
8606 TA04
L1
47µH
SYNC
INTVCC
TR/SS
RT
LT8606
GND
SW
PG
FB
R4
100k
R1
40.2k
L1 = MSS6132-473MLB
C4
22µF
X7R
1210
fSW = 1MHz
C2
4.7µF
X7R
1206
5V 2MHz Step Down
3.3V 2MHz Step Down
12V 1MHz Step Down
LT8606/LT8606B
20
Rev. D
For more information www.analog.com
VIN BST
EN/UV C1
0.1µF
C5
10pF
R2
1M
VIN
3.2V TO 20V
(42V TRANSIENT)
C6
10nF
C3
1µF
VOUT
1.8V
350mA
POWER GOOD
R3
768k
8606 TA05
L1
3.3µH
SYNC
INTVCC
TR/SS
RT
LT8606
GND
SW
PG
FB
R4
100k
R1
18.2k
L1 = XFL3010-332ME
C4
22µF
X7R
1206
fSW = 2MHz
C2
4.7µF
VIN BST
EN/UV C1
0.1µF
C5
47pF
R2
1M
VIN
5.8 TO 40V
C6
10nF
C3
1µF
VOUT
5V
350mA
POWER GOOD
R3
187k
8606 TA06
L1
27µH
L3
4.7µH
L2
BEAD
SYNC
INTVCC
TR/SS
RT
LT8606
(MSOP)
GND
SW
PG
FB
R4
100k
R1
60.4k
C4
22µF
X7R
1206
fSW = 700kHz
C2
4.7µF
C9
33µF
C7
4.7µF
C8
4.7µF
C8, C7, C2: X7R 1206
C9: 63SXV33M
L1: MSS5121-273
L2: MPZ2012S221AT000
L3: XAL4030-472
Ultralow EMI 5V 1.5A Step Down
1.8V 2MHz Step Down
TYPICAL APPLICATIONS
LT8606/LT8606B
21
Rev. D
For more information www.analog.com
PACKAGE DESCRIPTION
MSOP (MSE) 0213 REV I
0.53 ±0.152
(.021 ±.006)
SEATING
PLANE
0.18
(.007)
1.10
(.043)
MAX
0.17 –0.27
(.007 – .011)
TYP
0.86
(.034)
REF
0.50
(.0197)
BSC
1234 5
4.90 ±0.152
(.193 ±.006)
0.497 ±0.076
(.0196 ±.003)
REF
8910
10
1
76
3.00 ±0.102
(.118 ±.004)
(NOTE 3)
3.00 ±0.102
(.118 ±.004)
(NOTE 4)
NOTE:
1. DIMENSIONS IN MILLIMETER/(INCH)
2. DRAWING NOT TO SCALE
3. DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS.
MOLD FLASH, PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.152mm (.006") PER SIDE
4. DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS.
INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.152mm (.006") PER SIDE
5. LEAD COPLANARITY (BOTTOM OF LEADS AFTER FORMING) SHALL BE 0.102mm (.004") MAX
6. EXPOSED PAD DIMENSION DOES INCLUDE MOLD FLASH. MOLD FLASH ON E-PAD
SHALL NOT EXCEED 0.254mm (.010") PER SIDE.
0.254
(.010) 0° – 6° TYP
DETAIL “A”
DETAIL “A”
GAUGE PLANE
5.10
(.201)
MIN
3.20 – 3.45
(.126 – .136)
0.889 ±0.127
(.035 ±.005)
RECOMMENDED SOLDER PAD LAYOUT
1.68 ±0.102
(.066 ±.004)
1.88 ±0.102
(.074 ±.004)
0.50
(.0197)
BSC
0.305 ± 0.038
(.0120 ±.0015)
TYP
BOTTOM VIEW OF
EXPOSED PAD OPTION
1.68
(.066)
1.88
(.074)
0.1016 ±0.0508
(.004 ±.002)
DETAIL “B”
DETAIL “B”
CORNER TAIL IS PART OF
THE LEADFRAME FEATURE.
FOR REFERENCE ONLY
NO MEASUREMENT PURPOSE
0.05 REF
0.29
REF
MSE Package
10-Lead Plastic MSOP, Exposed Die Pad
(Reference LTC DWG # 05-08-1664 Rev I)
LT8606/LT8606B
22
Rev. D
For more information www.analog.com
PACKAGE DESCRIPTION
2.00 ±0.05
(4 SIDES)
2.00 SQ ±0.05
NOTE:
1. DRAWING IS NOT A JEDEC PACKAGE OUTLINE
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 0.15mm ON ANY SIDE
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
0.55 ±0.05
BOTTOM VIEW—EXPOSED PAD
0.23
REF
0.335
REF
0.335 REF
0.75 ±0.05
1
4
85
PIN 1 BAR
TOP MARK
(SEE NOTE 6)
0.200 REF
0.00 – 0.05
(DC8MA) DFN 0113 REV Ø
0.23 ±0.05
0.45 BSC
0.25 ±0.05
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED
0.90
REF
0.23
REF
0.85 ±0.05
1.8 REF
1.8 REF
2.60 ±0.05
PACKAGE
OUTLINE
0.45 BSC
PIN 1 NOTCH
R = 0.15
DC8 Package
8-Lead Plastic DFN (2mm × 2mm)
(Reference LTC DWG # 05-08-1939 Rev Ø)
Exposed Pad Variation AA
LT8606/LT8606B
23
Rev. D
For more information www.analog.com
Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog
Devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use. Specifications
subject to change without notice. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices.
REVISION HISTORY
REV DATE DESCRIPTION PAGE NUMBER
A 06/17 Added DFN package option
Clarified electrical parameters for DFN package option
Clarified graphs for MSOP package option
Clarified Pin Functions for DFN package option
Clarified Operation section to include DFN option
Clarified Applications last paragraph and Figure 2 to include DFN option
Clarified Applications section to include DFN operation
Added DFN Package Description
1,2
2,3
6,7
9
11
12
16,17
22
B 11/17 Added H-grade option
Clarified Oscillator Frequency RT conditions
Clarified efficiency graphs
Clarified Frequency Foldback graph
Clarified Switching Waveform graph
Clarified Block Diagram
Added Figure 5
Clarified Typical Applications for MSOP package option
2, 3
3
4
7
8
10
18
20, 24
C 07/18 Added B version
Added table to clarify versions
Modified text in Description to add DFN functionality
Added B version to Order Information
Clarified Minimum On-Time Conditions
Clarified Efficiency graphs
Clarified No-Load Supply Current graphs
Clarified Burst Frequency vs Output Current graph
Clarified Frequency Foldback graph
Clarified Pin Functions on SYNC and TR/SS
Clarified Operation third paragraph
Clarified last paragraph to include DFN B version
Clarified Applications Information to include DFN B version
Clarified Figure 5 PCB Layout
All
1
1
2
3
4
5
6
7
9
11
12
16, 17
18
D 11/20 AEC-Q100 Qualified for Automotive Applications
Added J-Grade to Operating Junction
Updated suffix for DC package
#W Materials added on
Changed Minimum On-Time conditions in the Electrical Characteristics table
1
2
2
2
3
LT8606/LT8606B
24
Rev. D
For more information www.analog.com
ANALOG DEVICES, INC. 2017-2020
D17104-0-11/20
www.analog.com
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5V and 3.3V with Ratio Tracking
VIN BST
EN/UV C1
0.1µF
C11, 10pF
R6, 1M
R2, 1M
R10
22k
R9
80.6k
C12
1µF
VOUT
3.3V
350mA
POWER GOOD
R7
309k
8606 TA07
L2
6.8µH
SYNC
INTVCC
TR/SS
RT
LT8606
(MSOP)
GND
SW
PG
FB
R8
100k
R5
18.2k
C2, C4, C8, C10: X7R 0805
L1: XFL3010-103ME
L2: XFL3010-682ME
C10
10µF
fSW = 2MHz
C8
1µF
VIN BST
EN/UV C1
0.1µF
C5, 10pF
VIN
5.6V TO 42V
C6
10nF
C3
1µF
VOUT
5V
350mA
POWER GOOD
R3
187k
L1
10µH
SYNC
INTVCC
TR/SS
RT
LT8606
(MSOP)
GND
SW
PG
FB
R4
100k
R1
18.2k
C4
10µF
fSW = 2MHz
C2
1µF