LT8610A/LT8610AB Series
1
8610abfa
For more information www.linear.com/LT8610A
TYPICAL APPLICATION
FEATURES DESCRIPTION
42V, 3.5A Synchronous
Step-Down Regulator with
2.5µA Quiescent Current
The LT
®
8610A/LT8610AB series are compact, high ef-
ficiency, high speed synchronous monolithic step-down
switching regulators that consume only 2.5µA of quies-
cent current. Compared to the LT8610, they have higher
maximum output currents of 3.5A and a faster minimum
switch-on time of 30ns. The LT8610A has the same low
ripple burst mode performance of the LT8610, while the
LT8610AB has even higher light load efficiency.
The other features of the LT8610 remain unchanged in the
LT8610A/LT8610AB series. A SYNC pin allows synchroni-
zation to an external clock. The EN/UV pin has an accurate
1V threshold for VIN undervoltage lockout or shut down.
A capacitor on the TR/SS pin programs the output voltage
ramp rate during startup. The PG flag signals when VOUT
is within ±9% of the programmed output voltage as well
as fault conditions.
OUTPUT
CURRENT
MINIMUM
ON TIME
1mA LOAD
EFFICIENCY**
LT8610* 2.5A 50ns 82%
LT8610A 3.5A 30ns 82%
LT8610AB 3.5A 30ns 91%
*See LT8610 data sheet. **VIN = 12V, VOUT = 3.3V, L = 4.7µH
5V 3.5A Step-Down Converter
APPLICATIONS
n LT8610 Feature Set, Plus:
3.5A Maximum Output Current
Fast 30ns Minimum Switch-On Time
Improved Burst Mode Efficiency (LT8610AB Only)
Improved EMI
n Wide Input Voltage Range: 3.4V to 42V
n Ultralow Quiescent Current Burst Mode
®
Operation:
2.5μA IQ Regulating 12VIN to 3.3VOUT
n Fixed Output Voltages: 3.3V, 5V
n Output Ripple < 10mVP-P (LT8610A Only)
n High Efficiency Synchronous Operation:
95% Efficiency at 1A, 5VOUT from 12VIN
93% Efficiency at 1A, 3.3VOUT from 12VIN
n Low Dropout Under All Conditions: 200mV at 1A
n Safely Tolerates Inductor Saturation in Overload
n Adjustable and Synchronizable Frequency:
200kHz to 2.2MHz
n Accurate 1V Enable Pin Threshold
n Output Soft-Start and Tracking
n Small Thermally Enhanced 16-Lead MSOP Package
n Automotive and Industrial Supplies
n GSM Power Supplies
L, LT , LT C , LT M , Burst Mode, Linear Technology and the Linear logo are registered trademarks
of Linear Technology Corporation. All other trademarks are the property of their respective
owners.
BSTVIN
EN/UV
PG
SYNC
INTVCC
TR/SS
RT
SW
LT8610AB-5
GND
BIAS
8610ab TA01a
VOUT
0.1µF
V
OUT
5V
3.5A
4.7µF
V
IN
5.5V TO 42V
1µF
10nF
4.7µH
f
SW
= 700kHz
60.4k
47µF
×2
LT8610AB Efficiency at 5VOUT
0.1 1 100010010
LOAD CURRENT (mA)
EFFICIENCY (%)
80
90
100
8610ab TA01b
70
50
60
40
30
VIN = 12V
VIN = 24V
VIN = 36V
LT8610A/LT8610AB Series
2
8610abfa
For more information www.linear.com/LT8610A
ABSOLUTE MAXIMUM RATINGS
VIN, EN/UV, PG ..........................................................42V
BIAS .......................................................................... 30V
BST Pin Above SW Pin................................................4V
FB, TR/SS, RT, INTVCC . .............................................. 4V
VOUT, SYNC Voltage . ..................................................6V
Operating Junction Temperature Range (Note 2)
LT8610AE/LT8610ABE ........................... –40 to 125°C
LT8610AI/LT8610ABI ............................. –40 to 125°C
LT8610AH/LT8610ABH ..........................–40 to 150°C
Storage Temperature Range ......................–65 to 150°C
(Note 1)
ORDER INFORMATION
LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE
LT8610AEMSE#PBF LT8610AEMSE#TRPBF 8610A 16-Lead Plastic MSOP –40°C to 125°C
LT8610AEMSE-3.3#PBF LT8610AEMSE-3.3#TRPBF 610A33 16-Lead Plastic MSOP –40°C to 125°C
LT8610AEMSE-5#PBF LT8610AEMSE-5#TRPBF 8610A5 16-Lead Plastic MSOP –40°C to 125°C
LT8610AIMSE#PBF LT8610AIMSE#TRPBF 8610A 16-Lead Plastic MSOP –40°C to 125°C
LT8610AIMSE-3.3#PBF LT8610AIMSE-3.3#TRPBF 610A33 16-Lead Plastic MSOP –40°C to 125°C
LT8610AIMSE-5#PBF LT8610AIMSE-5#TRPBF 8610A5 16-Lead Plastic MSOP –40°C to 125°C
LT8610AHMSE#PBF LT8610AHMSE#TRPBF 8610A 16-Lead Plastic MSOP –40°C to 150°C
LT8610AHMSE-3.3#PBF LT8610AHMSE-3.3#TRPBF 610A33 16-Lead Plastic MSOP –40°C to 150°C
LT8610AHMSE-5#PBF LT8610AHMSE-5#TRPBF 8610A5 16-Lead Plastic MSOP –40°C to 150°C
LT8610ABEMSE#PBF LT8610ABEMSE#TRPBF 8610AB 16-Lead Plastic MSOP –40°C to 125°C
LT8610ABEMSE-3.3#PBF LT8610ABEMSE-3.3#TRPBF 10AB33 16-Lead Plastic MSOP –40°C to 125°C
LT8610ABEMSE-5#PBF LT8610ABEMSE-5#TRPBF 610AB5 16-Lead Plastic MSOP –40°C to 125°C
LT8610ABIMSE#PBF LT8610ABIMSE#TRPBF 8610AB 16-Lead Plastic MSOP –40°C to 125°C
LT8610ABIMSE-3.3#PBF LT8610ABIMSE-3.3#TRPBF 10AB33 16-Lead Plastic MSOP –40°C to 125°C
LT8610ABIMSE-5#PBF LT8610ABIMSE-5#TRPBF 610AB5 16-Lead Plastic MSOP –40°C to 125°C
LT8610ABHMSE#PBF LT8610ABHMSE#TRPBF 8610AB 16-Lead Plastic MSOP –40°C to 150°C
LT8610ABHMSE-3.3#PBF LT8610ABHMSE-3.3#TRPBF 10AB33 16-Lead Plastic MSOP –40°C to 150°C
LT8610ABHMSE-5#PBF LT8610ABHMSE-5#TRPBF 610AB5 16-Lead Plastic MSOP –40°C to 150°C
Consult LT C Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container.
Consult LT C Marketing for information on non-standard lead based finish parts.
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/
LT8610A, LT8610AB LT8610A-3.3, LT8610A-5, LT8610AB-3.3, LT8610AB-5
1
2
3
4
5
6
7
8
SYNC
TR/SS
RT
EN/UV
VIN
VIN
NC
GND
16
15
14
13
12
11
10
9
FB
PG
BIAS
INTV
CC
BST
SW
SW
SW
TOP VIEW
17
GND
MSE PACKAGE
16-LEAD PLASTIC MSOP
θJA = 40°C/W, θJC(PAD) = 10°C/W
EXPOSED PAD (PIN 17) IS GND, MUST BE SOLDERED TO PCB
1
2
3
4
5
6
7
8
SYNC
TR/SS
RT
EN/UV
VIN
VIN
NC
GND
16
15
14
13
12
11
10
9
VOUT
PG
BIAS
INTV
CC
BST
SW
SW
SW
TOP VIEW
17
GND
MSE PACKAGE
16-LEAD PLASTIC MSOP
θJA = 40°C/W, θJC(PAD) = 10°C/W
EXPOSED PAD (PIN 17) IS GND, MUST BE SOLDERED TO PCB
PIN CONFIGURATION
LT8610A/LT8610AB Series
3
8610abfa
For more information www.linear.com/LT8610A
ELECTRICAL CHARACTERISTICS
The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C.
PARAMETER CONDITIONS MIN TYP MAX UNITS
Minimum Input Voltage (Note 4) l2.9 3.4 V
VIN Quiescent Current VEN/UV = 0V
l
1.0
1.0
3
8
µA
µA
VEN/UV = 2V, Not Switching, VSYNC = 0V
l
1.7
1.7
4
10
µA
µA
VEN/UV = 2V, Not Switching, VSYNC = 2V 0.26 0.5 mA
VIN Current in Regulation VOUT = 0.97V, VIN = 6V, Output Load = 100µA (LT8610A)
VOUT = 0.97V, VIN = 6V, Output Load = 1mA (LT8610A)
VOUT = 0.97V, VIN = 6V, Output Load = 100µA (LT8610AB)
VOUT = 0.97V, VIN = 6V, Output Load = 1mA (LT8610AB)
l
l
l
l
24
210
24
210
50
350
50
350
µA
µA
µA
µA
VIN Current in Regulation VOUT = 3.3V, VIN = 8V, Output Load = 100µA (LT8610A-3.3)
VOUT = 3.3V, VIN = 8V, Output Load = 1mA (LT8610A-3.3)
VOUT = 3.3V, VIN = 8V, Output Load = 100µA (LT8610AB-3.3)
VOUT = 3.3V, VIN = 8V, Output Load = 1mA (LT8610AB-3.3)
VOUT = 5V, VIN = 8V, Output Load = 100µA (LT8610A-5)
VOUT = 5V, VIN = 8V, Output Load = 1mA (LT8610A-5)
VOUT = 5V, VIN = 8V, Output Load = 100µA (LT8610AB-5)
VOUT = 5V, VIN = 8V, Output Load = 1mA (LT8610AB-5)
l
l
l
l
l
l
l
l
60
540
55
500
100
790
80
730
120
900
100
800
180
1200
150
1100
µA
µA
µA
µA
µA
µA
µA
µA
Feedback Reference Voltage
(LT8610A/LT8610AB)
VIN = 6V, ILOAD = 0.5A
VIN = 6V, ILOAD = 0.5A
l
0.964
0.958
0.970
0.970
0.976
0.982
V
V
Output Voltage
(LT8610A-3.3/LT8610AB-3.3)
VIN = 8V, ILOAD = 0.5A
VIN = 8V, ILOAD = 0.5A
l
3.28
3.26
3.30
3.30
3.32
3.34
V
V
Output Voltage
(LT8610A-5/LT8610AB-5)
VIN = 8V, ILOAD = 0.5A
VIN = 8V, ILOAD = 0.5A
l
4.97
4.94
5.00
5.00
5.03
5.06
V
V
Feedback Voltage Line Regulation
(LT8610A/LT8610AB)
VIN = 4V to 42V, ILOAD = 1A l0.004 0.02 %/V
Voltage Line Regulation
(LT8610A-3.3/LT8610AB-3.3)
VIN = 4V to 42V, ILOAD = 1A l0.004 0.02 %/V
Voltage Line Regulation
(LT8610A-5/LT8610AB-5)
VIN = 6V to 42V, ILOAD = 1A l0.004 0.02 %/V
Feedback Pin Input Current
(LT8610A/LT8610AB)
VFB = 1V –20 20 nA
Internal Feedback Resistor Divider
(LT8610A-3.3/LT8610AB-3.3)
14.3 MΩ
Internal Feedback Resistor Divider
(LT8610A-5/LT8610AB-5)
12.5 MΩ
INTVCC Voltage ILOAD = 0mA, VBIAS = 0V
ILOAD = 0mA, VBIAS = 3.3V
3.23
3.25
3.4
3.29
3.57
3.35
V
V
INTVCC Undervoltage Lockout 2.5 2.6 2.7 V
BIAS Pin Current Consumption VBIAS = 3.3V, ILOAD = 1A, 2MHz 9 mA
Minimum On-Time ILOAD = 1A, SYNC = 0V
ILOAD = 1A, SYNC = 3.3V
l
l
15
15
30
30
45
45
ns
ns
Minimum Off-Time 95 125 ns
LT8610A/LT8610AB Series
4
8610abfa
For more information www.linear.com/LT8610A
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
Oscillator Frequency RT = 221k, ILOAD = 1A
RT = 60.4k, ILOAD = 1A
RT = 18.2k, ILOAD = 1A
l
l
l
180
665
1.85
210
700
2.00
240
735
2.15
kHz
kHz
MHz
Top Power NMOS On-Resistance ISW = 1A 120 mΩ
Top Power NMOS Current Limit LT8610A
LT8610AB
l
l
5
5
6.7
6.7
8
8
A
A
Bottom Power NMOS On-Resistance VINTVCC = 3.4V, ISW = 1A 65 mΩ
Bottom Power NMOS Current Limit VINTVCC = 3.4V 3.4 4.3 5.4 A
SW Leakage Current VIN = 42V, VSW = 0V, 42V –1.5 1.5 µA
EN/UV Pin Threshold EN/UV Rising l0.94 1.0 1.06 V
EN/UV Pin Hysteresis 40 mV
EN/UV Pin Current VEN/UV = 2V –20 20 nA
PG Upper Threshold Offset from VFB VFB Falling l6 9.0 12 %
PG Lower Threshold Offset from VFB VFB Rising l–12 –9.0 –6 %
PG Hysteresis 1.3 %
PG Leakage VPG = 3.3V –40 40 nA
PG Pull-Down Resistance VPG = 0.1V l680 2000 Ω
SYNC Threshold SYNC Falling
SYNC Rising
0.8
1.6
1.1
2.0
1.4
2.4
V
V
SYNC Pin Current VSYNC = 6V –40 40 nA
TR/SS Source Current l1.0 2.0 3.2 µA
TR/SS Pull-Down Resistance Fault Condition, TR/SS = 0.1V 230 Ω
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 LT8610AE/LT8610ABE 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 LT8610AI/LT8610ABI is guaranteed over the full –40°C to 125°C
operating junction temperature range. The LT8610AH 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.
Note 4: For fixed output voltage versions, minimum input voltage will be
limited by output voltage.
LT8610A/LT8610AB Series
5
8610abfa
For more information www.linear.com/LT8610A
TYPICAL PERFORMANCE CHARACTERISTICS
LT8610AB Efficiency at 3.3VOUT LT8610A Efficiency at 5VOUT LT8610A Efficiency at 5VOUT
LT8610A Efficiency at 3.3VOUT LT8610A Efficiency at 3.3VOUT
LT8610A/LT8610AB
Efficiency vs Frequency at 1A
LT8610AB Efficiency at 5VOUT LT8610AB Efficiency at 5VOUT LT8610AB Efficiency at 3.3VOUT
LOAD CURRENT (A)
0
EFFICIENCY (%)
80
90
100
2 3
8610ab G01
70
60
75
85
95
65
55
50 0.5 11.5
3.5
2.5
fSW = 700kHz
L = IHLP-2020BZ-01, 4.7µH
VIN = 12V
VIN = 24V
VIN = 36V
LOAD CURRENT (mA)
EFFICIENCY (%)
0.01 101 1000100
8610ab G03
0.1
80
90
100
70
50
60
40
20
30 VIN = 12V
VIN = 24V
VIN = 36V
fSW = 700kHz
L = IHLP-2020BZ-01, 4.7µH
0 2 3
0.5 11.5
3.5
2.5
LOAD CURRENT (A)
EFFICIENCY (%)
80
90
100
8610ab G02
70
60
75
85
95
65
55
50
VIN = 12V
VIN = 24V
VIN = 36V
fSW = 700kHz
L = IHLP-2020BZ-01, 4.7µH
0.01 101 10001000.1
VIN = 12V
VIN = 24V
VIN = 36V
LOAD CURRENT (mA)
30
EFFICIENCY (%)
90
100
80
50
70
60
40
8610ab G04
20
fSW = 700kHz
L = IHLP-2020BZ-01, 4.7µH
LOAD CURRENT (A)
0
EFFICIENCY (%)
80
90
100
2 3
8610ab G42
70
60
75
85
95
65
55
50 0.5 11.5
3.5
2.5
fSW = 700kHz
L = IHLP-2020BZ-01, 4.7µH
VIN = 12V
VIN = 24V
VIN = 36V
LOAD CURRENT (mA)
EFFICIENCY (%)
0.01 101 1000100
8610ab G43
0.1
80
90
100
70
50
60
40
20
30 VIN = 12V
VIN = 24V
VIN = 36V
fSW = 700kHz
L = IHLP-2020BZ-01, 4.7µH
0 2 3
0.5 11.5
3.5
2.5
LOAD CURRENT (A)
EFFICIENCY (%)
80
90
100
8610ab G44
70
60
75
85
95
65
55
50
VIN = 12V
VIN = 24V
VIN = 36V
fSW = 700kHz
L = IHLP-2020BZ-01, 4.7µH
0.01 101 10001000.1
VIN = 12V
VIN = 24V
VIN = 36V
LOAD CURRENT (mA)
30
EFFICIENCY (%)
90
100
80
50
70
60
40
8610ab G45
20
fSW = 700kHz
L = IHLP-2020BZ-01, 4.7µH
SWITCHING FREQUENCY (MHz)
0.25
80
85
100
1.75
8610ab G05
75
70
0.75 1.25
2.25
1.50
0.50 1.00 2.00
65
60
90
95
EFFICIENCY (%)
VIN = 12V
VIN = 24V
VOUT = 3.3V
L = IHLP-2020BZ-01, 4.7µH
LT8610A/LT8610AB Series
6
8610abfa
For more information www.linear.com/LT8610A
TYPICAL PERFORMANCE CHARACTERISTICS
Line Regulation
LT8610A No Load Supply Current
LT8610AB No Load
Supply Current No Load Supply Current
Reference Voltage LT8610A-3.3 Output Voltage LT8610AB-3.3 Output Voltage
EN Pin Thresholds Load Regulation
TEMPERATURE (°C)
–55
0.955
REFERENCE VOLTAGE (V)
0.958
0.964
0.967
0.970
0.985
0.976
565 95 125
8610ab G06
0.961
0.979
0.982
0.973
–25 35
155
TEMPERATURE (°C)
–55
3.240
OUTPUT VOLTAGE (V)
3.255
3.285
3.300
3.315
3.360
3.345
565 95 125
8610ab G46
3.270
3.330
–25 35
155
TEMPERATURE (°C)
–55
4.900
OUTPUT VOLTAGE (V)
4.925
4.975
5.000
5.025
5.100
5.075
5 65 95 125
8610ab G47
4.950
5.050
–25 35
155
TEMPERATURE (°C)
–55
EN THRESHOLD (V)
65
8610ab G07
5
–25 95 125
35
155
0.95
0.96
0.98
0.99
1.00
1.02
0.97
1.01
EN RISING
EN FALLING
LOAD CURRENT (A)
0
–0.25
CHANGE IN V
OUT
(%)
–0.15
–0.05
0.05
0.5 11.5 2
8610ab G08
2.5
0.15
0.25
–0.20
–0.10
0
0.10
0.20
3.5
3
VOUT = 3.3V
VIN = 12V
INPUT VOLTAGE (V)
0
CHANGE IN V
OUT
(%)
0.03
0.09
0.15
40
8610ab G09
–0.03
–0.09
0
0.06
0.12
–0.06
–0.12
–0.15 105 2015 30 35
45
25
VOUT = 3.3V
ILOAD = 0.5A
INPUT VOLTAGE (V)
0
0
INPUT CURRENT (µA)
0.5
1.5
2.0
2.5
5.0
3.5
10 20 25
40
8610ab G10
1.0
4.0
4.5
3.0
5 15 30 35
TESTED IN REGULATION
8610A: VOUT = 3.3V
8610A-3.3
8610A-5
8610A
INPUT VOLTAGE (V)
0
0
INPUT CURRENT (µA)
0.5
1.5
2.0
2.5
5.0
3.5
10 20 25
40
8610ab G48
1.0
4.0
4.5
3.0
5 15 30 35
TESTED IN REGULATION
8610AB: VOUT = 3.3V
8610AB-3.3
8610AB-5
8610AB
TEMPERATURE (°C)
–55 –25
0
INPUT CURRENT (µA)
10
25
565 95
8610ab G11
5
20
15
35 125
155
VOUT = 3.3V
VIN = 12V
IN REGULATION
LT8610A/LT8610AB Series
7
8610abfa
For more information www.linear.com/LT8610A
Top FET Current Limit vs Duty Cycle Top FET Current Limit Bottom FET Current Limit
DUTY CYCLE
0
CURRENT LIMIT (A)
3.5
4.0
4.5
0.6
1.0
8610ab G13
3.0 0.2 0.4 0.8
5.0
5.5
8.0
7.0
7.5
6.5
6.0
TEMPERATURE (°C)
–55
4.50
CURRENT LIMIT (A)
4.75
5.00
5.25
5.50
5.75
6.00
6.25
6.50
6.75
7.00
–25 5 35 65
8610ab G14
95
125
30% DC
TEMPERATURE (°C)
–55
3.00
CURRENT LIMIT (A)
3.25
3.50
3.75
4.00
5.50
–25 5 35 65
8610ab G15
95
155
125
4.25
4.50
4.75
5.00
5.25
TYPICAL PERFORMANCE CHARACTERISTICS
Minimum On-Time
Minimum Off-Time Dropout Voltage Switching Frequency
Switch Drop Switch Drop
TEMPERATURE (°C)
–55 –25
0
SWITCH DROP (mV)
100
250
565 95
8610ab G40
50
200
150
35 125
155
TOP SW
BOT SW
SWITCH CURRENT = 1A
SWITCH CURRENT (A)
0
0
SWITCH DROP (mV)
50
150
200
250
2
450
8610ab G41
100
1
0.5 2.5
1.5
3
300
350
400
TOP SW
BOT SW
TEMPERATURE (°C)
–55
25
27
29
31
MINIMUM ON-TIME (ns)
33
35
37
39
45
5 65 95 125
8610ab G17
43
41
–25 35
155
VOUT = 3.3V
VOUT = 0.97V
ILOAD = 1.5A
VSYNC = 0V
TEMPERATURE (°C)
–50
MINIMUM OFF-TIME (ns)
95
35
8610ab G18
80
–25 5 65
75
125
120
115
110
105
100
90
85
95 125
155
VOUT = 3.3V
ILOAD = 0.5A
LOAD CURRENT (A)
DROPOUT VOLTAGE (V)
400
8610ab G19
200
0
600
800
300
100
500
700
0 0.5 11.5 2 2.5
3.5
3
TEMPERATURE (°C)
–55
SWITCHING FREQUENCY (kHz)
730
35
8610ab G20
700
680
–25 5 65
670
660
740
RT = 60.4k
720
710
690
95 125
155
LT8610A/LT8610AB Series
8
8610abfa
For more information www.linear.com/LT8610A
TYPICAL PERFORMANCE CHARACTERISTICS
Soft-Start Tracking Soft-Start Current PG High Thresholds
RT Programmed Switching
FrequencyPG Low Thresholds VIN UVLO
TR/SS VOLTAGE (V)
0
FB VOLTAGE (V)
0.8
1.0
1.2
0.6 1.0
8610ab G23
0.6
0.4
0.2 0.4 0.8 1.2
1.4
0.2
0
TEMPERATURE (°C)
–50
SS PIN CURRENT (µA)
2.3
35
8610ab G24
2.0
1.8
–25 5 65
1.7
1.6
2.4
2.2
2.1
1.9
95 125
155
VSS = 0.5V
TEMPERATURE (°C)
–55
7.0
PG THRESHOLD OFFSET FROM V
REF
(%)
7.5
8.5
9.0
9.5
12.0
10.5
565 95 125
8610ab G25
8.0
11.0
11.5
10.0
–25 35
155
FB RISING
FB FALLING
SWITCHING FREQUENCY (MHz)
0.2
RT PIN RESISTOR (kΩ)
150
200
250
1.8
8610ab G27
100
50
125
175
225
75
25
00.6 11.4
2.2
TEMPERATURE (°C)
–55
INPUT VOLTAGE (V)
3.4
35
8610ab G28
2.8
2.4
–25 5 65
2.2
2.0
3.6
3.2
3.0
2.6
95 125
155
TEMPERATURE (°C)
–55
–12.0
PG THRESHOLD OFFSET FROM V
REF
(%)
–11.5
–10.5
–10.0
–9.5
–7.0
–8.5
565 95 125
8610ab G26
–11.0
–8.0
–7.5
–9.0
–25 35
155
FB RISING
FB FALLING
Minimum Load to Full Frequency Burst Frequency Frequency Foldback
INPUT VOLTAGE (V)
LOAD CURRENT (mA)
60
70
80
15 25
40
8610ab G39
40
20
0
50
30
10
5 10 20 30 35
VOUT = 3.3V
fSW = 700kHz
PULSE-SKIPPING MODE
FB VOLTAGE (V)
0
SWITCHING FREQUENCY (kHz)
300
400
500
0.6
1
8610ab G22
200
100
00.2 0.4 0.8
600
700
800
VOUT = 3.3V
VIN = 12V
VSYNC = 0V
RT = 60.4k
LOAD CURRENT (mA)
0
SWITCHING FREQUENCY (kHz)
400
500
600
800
8610ab G21
300
200
0200 400 600 700100 300 500
100
800
VIN = 12V
VOUT = 3.3V
L = 4.7µH
LT8610A
LT8610AB
700
LT8610A/LT8610AB Series
9
8610abfa
For more information www.linear.com/LT8610A
Bias Pin Current Bias Pin Current
INPUT VOLTAGE (V)
5
BIAS PIN CURRENT (mA)
4.5
5.5
45
8610ab G29
3.5
2.5 15 25 35
10 20 30 40
6.5
4.0
5.0
3.0
6.0
VBIAS = 5V
VOUT = 5V
ILOAD = 1A
fSW = 700kHz
SWITCHING FREQUENCY (MHz)
0
0
BIAS PIN CURRENT (mA)
2
4
6
8
10
12
0.5 1 1.5 2
8610ab G30
2.5
VBIAS = 5V
VOUT = 5V
VIN = 12V
ILOAD = 1A
TYPICAL PERFORMANCE CHARACTERISTICS
Switching Waveforms
Switching Waveforms Switching Waveforms
LT8610A/LT8610AB
Transient Response
LT8610A/LT8610AB
Transient Response Start-Up Dropout Performance Start-Up Dropout Performance
IL
1A/DIV
VSW
5V/DIV
500ns/DIV
12VIN TO 5VOUT AT 1A
8610ab
G31
IL
200mA/DIV
VSW
5V/DIV
500µs/DIV
12VIN TO 5VOUT AT 10mA
VSYNC = 0V
(LT8610A)
8610ab
G32
IL
1A/DIV
VSW
10V/DIV
500ns/DIV
36VIN TO 5VOUT AT 1A
8610ab
G33
IL
2A/DIV
VOUT
200mV/DIV
50µs/DIV
1.5A TO 3.5A TRANSIENT
12VIN, 3.3VOUT
COUT
= 47µF
8610ab
G34
IL
2A/DIV
VOUT
200mV/DIV
50µs/DIV
30mA TO 2A TRANSIENT
12VIN, 3.3VOUT
C
OUT
= 47µF
8610ab
G35
VIN
2V/DIV
VOUT
2V/DIV
100ms/DIV
2.5Ω LOAD
(2A IN REGULATION)
8610ab
G37
VIN
VOUT
VIN
2V/DIV
VOUT
2V/DIV
100ms/DIV
20Ω LOAD
(250mA IN REGULATION)
8610ab
G38
VIN
VOUT
LT8610A/LT8610AB Series
10
8610abfa
For more information www.linear.com/LT8610A
PIN FUNCTIONS
SYNC (Pin 1): 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. Apply a DC voltage of 3V or higher
or tie to INTVCC for pulse-skipping mode. When in pulse-
skipping mode, the IQ will increase to several hundred µA.
Do not float this pin.
TR/SS (Pin 2): Output Tracking and Soft-Start Pin. This
pin allows user control of output voltage ramp rate dur-
ing start-up. A TR/SS voltage below 0.97V forces the
LT8610A/LT8610AB to regulate the FB pin to equal the
TR/SS pin voltage. When TR/SS is above 0.97V, the
tracking function is disabled and the internal reference
resumes control of the error amplifier. An internal 2.2μA
pull-up current from INTVCC on this pin allows a capacitor
to program output voltage slew rate. This pin is pulled to
ground with an internal 230Ω MOSFET during shutdown
and fault conditions; use a series resistor if driving from
a low impedance output. This pin may be left floating if
the tracking function is not needed.
RT (Pin 3): A resistor is tied between RT and ground to
set the switching frequency.
EN/UV (Pin 4): The LT8610A/LT8610AB is shut down
when this pin is low and active when this pin is high. The
hysteretic threshold voltage is 1.00V going up and 0.96V
going down. Tie to VIN if the shutdown feature is not
used. An external resistor divider from VIN can be used
to program a VIN threshold below which the LT8610A/
LT8610AB will shut down.
VIN (Pins 5, 6): The VIN pins supply current to the LT8610A/
LT8610AB internal circuitry and to the internal topside
power switch. These pins must be tied together and 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.
NC (Pin 7): No Connect. This pin is not connected to
internal circuitry.
SW (Pins 9, 10, 11): The SW pins are the outputs of the
internal power switches. Tie these pins together and con-
nect them to the inductor and boost capacitor. This node
should be kept small on the PCB for good performance.
BST (Pin 12): 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.
INTVCC (Pin 13): Internal 3.4V Regulator Bypass Pin.
The internal power drivers and control circuits are pow-
ered from this voltage. INTVCC maximum output cur-
rent is 20mA. Do not load the INTVCC pin with external
circuitry. INTVCC current will be supplied from BIAS if
VBIAS > 3.1V, otherwise current will be drawn from VIN.
Voltage on INTVCC will vary between 2.8V and 3.4V when
VBIAS is between 3.0V and 3.6V. Decouple this pin to power
ground with at least a 1μF low ESR ceramic capacitor
placed close to the IC.
BIAS (Pin 14): The internal regulator will draw current from
BIAS instead of VIN when BIAS is tied to a voltage higher
than 3.1V. For output voltages of 3.3V and above this pin
should be tied to VOUT. If this pin is tied to a supply other
than VOUT use a 1µF local bypass capacitor on this pin.
PG (Pin 15): The PG pin is the open-drain output of an
internal comparator. PG remains low until the FB pin is
within ±9% of the final regulation voltage, and there are
no fault conditions. PG is valid when VIN is above 3.4V,
regardless of EN/UV pin state.
FB (Pin 16, LT8610A/LT8610AB Only): The LT8610A/
LT8610AB regulates the FB pin to 0.970V. Connect the
feedback resistor divider tap to this pin. Also, connect a
phase lead capacitor between FB and VOUT. Typically, this
capacitor is 4.7pF to 10pF.
VOUT (Pin 16, LT8610A-3.3/LT8610A-5/LT8610AB-3.3/
LT8610AB-5 Only): The LT8610A-3.3 and LT8610AB-3.3
regulate the VOUT pin to 3.3V. This pin connects to a 14.3MΩ
internal feedback divider that programs the fixed output.
The LT8610A-5 and LT8610AB-5 regulate the VOUT pin
to 5V. This pin connects to a 12.5MΩ internal feedback
divider that programs the fixed output.
GND (Pin 8, Exposed Pad Pin 17): Ground. These pins
are the return path of the internal bottom-side switch and
must be tied together. Place the negative terminal of the
input capacitor as close to the GND pin and exposed pad
as possible. The exposed pad must be soldered to the PCB
in order to lower the thermal resistance.
LT8610A/LT8610AB Series
11
8610abfa
For more information www.linear.com/LT8610A
BLOCK DIAGRAM
+
+
–
+
–
SLOPE COMP
INTERNAL 0.97V REF
OSCILLATOR
200kHz TO 2.2MHz
BURST
DETECT
3.4V
REG
M1
M2
CBST
COUT
V
OUT
8610ab BD
SW L
BST
9-11
SWITCH
LOGIC
AND
ANTI-
SHOOT
THROUGH
ERROR
AMP
SHDN
±9%
VC
SHDN
TSD
INTVCC UVLO
VIN UVLO
LT8610A-3.3/LT8610A-5
LT8610AB-3.3/LT8610AB-5
ONLY
LT8610A/LT8610AB
ONLY
SHDN
TSD
VIN UVLO
EN/UV
1V +
–
4
12
3RT 1SYNC 17
GND
INTVCC 13
BIAS 14
GND
8
PG
15
FB
R1C1
R3
OPT
R4
OPT
R2
R2
RT
CSS
OPT
VOUT
16
TR/SS
2.2µA
2
VIN
VIN
CIN
CVCC
5, 6
R1
C1
VOUT
VOUT 16
LT8610A/LT8610AB Series
12
8610abfa
For more information www.linear.com/LT8610A
OPERATION
The LT8610A/LT8610AB 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 internal 0.97V 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 overload conditions result in more than 3.3A
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 LT8610A/LT8610AB is shut
down and draws 1µA from the input. When the EN/UV pin
is above 1V, the switching regulator will become active.
To optimize efficiency at light loads, the LT8610A/
LT8610AB operates in Burst Mode operation in 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, 2.5μA
will be consumed from the input supply when regulating
with no load. The SYNC pin is tied low to use Burst Mode
operation and can be tied to a logic high 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-skipping 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 hundred µA.
To improve efficiency across all loads, supply current to
internal circuitry can be sourced from the BIAS pin when
biased at 3.3V or above. Else, the internal circuitry will
draw current from VIN. The BIAS pin should be connected
to VOUT if the LT8610A/LT8610AB output is programmed
at 3.3V or above.
Comparators monitoring the FB pin voltage (or VOUT pin
voltages for fixed output versions) will pull the PG pin low
if the output voltage varies more than ±9% (typical) from
the set point, or if a fault condition is present.
The oscillator reduces the LT8610A/LT8610AB’s operating
frequency when the voltage at the FB pin (or VOUT pin for
fixed output versions) is low. This frequency foldback helps
to control the inductor current when the output voltage is
lower than the programmed value which occurs during
start-up or overcurrent conditions. When a clock is ap-
plied to the SYNC pin or the SYNC pin is held DC high, the
frequency foldback is disabled and the switching frequency
will slow down only during overcurrent conditions.
The LT8610AB differs from the LT8610A in that it has
improved efficiency during Burst Mode operation. This
comes with the trade-off of increased output voltage
ripple, which can be proportionally decreased with an
increase in output capacitance. The other trade-off is that
the LT8610AB will not reach the full switching frequency
programmed by the RT pin resistor until a higher load
compared to the LT8610A.
LT8610A/LT8610AB Series
13
8610abfa
For more information www.linear.com/LT8610A
(2a)
(2b)
APPLICATIONS INFORMATION
resulting in much higher light load efficiency than for typi-
cal converters. By maximizing the time between pulses,
the converter quiescent current approaches 2.5µA for a
typical 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.
The fixed output versions of the LT8610A/LT8610AB series
have larger internal feedback resistors than can practically
be used externally, so are a good choice for optimizing
quiescent current performance.
While in Burst Mode operation the current limit of the
top switch is approximately 400mA for the LT8610A
resulting in output voltage ripple shown in Figure 2a. The
LT8610AB has a 1A current limit in Burst Mode operation,
which increases the efficiency but also the output voltage
ripple compared to the the LT8610A (Figure 2b). However,
increasing the output capacitance will decrease the output
ripple proportionally (Table 1). 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 Figure 1a. The output load at
Figure 1. SW Frequency vs Load Information in
Burst Mode Operation (1a) and Pulse-Skipping Mode (1b)
Figure 2. Burst Mode Operation of LT8610A (2a) and
LT8610AB (2b)
Minimum Load to Full Frequency
Burst Frequency
(1a)
(1b)
LOAD CURRENT (mA)
0
SWITCHING FREQUENCY (kHz)
400
500
600
800
8610ab F01a
300
200
0200 400 600 700100 300 500
100
800
VIN = 12V
VOUT = 3.3V
L = 4.7µH
LT8610A
LT8610AB
700
INPUT VOLTAGE (V)
LOAD CURRENT (mA)
60
70
80
15 25
40
8610ab F01b
40
20
0
50
30
10
5 10 20 30 35
VOUT = 3.3V
fSW = 700kHz
PULSE-SKIPPING MODE
IL
200mA/DIV
VOUT
10mV/DIV
5µs/DIVVSYNC = 0V
COUT = 47µF
L = 4.7µH
8610ab F02a
LT8610A
IL
500mA/DIV
VOUT
20mV/DIV
VSW
5V/DIV
20µs/DIVVSYNC = 0V
COUT = 47µF
L = 4.7µH
8610ab F02b
LT8610AB
Achieving Ultralow Quiescent Current
To enhance efficiency at light loads, the LT8610A/LT8610AB
operates in low ripple Burst Mode operation, which keeps
the output capacitor charged to the desired output voltage
while minimizing the input quiescent current and minimiz-
ing output voltage ripple. In Burst Mode operation the
LT8610A/LT8610AB delivers single pulses of current to
the output capacitor followed by sleep periods where the
output power is supplied by the output capacitor. While
in sleep mode the LT8610A/LT8610AB consumes 1.7μA.
As the output load decreases, the frequency of single cur-
rent pulses decreases (see Figure 1a) and the percentage
of time the LT8610A/LT8610AB is in sleep mode increases,
LT8610A/LT8610AB Series
14
8610abfa
For more information www.linear.com/LT8610A
APPLICATIONS INFORMATION
which the LT8610A/LT8610AB reaches the programmed
frequency varies based on input voltage, output voltage,
and inductor choice. However, the output load required
to reach full frequency will be higher for the LT8610AB
as compared to the LT8610A (Figure 1a).
Inductor value has a very strong effect on Burst Mode ef-
ficiency. Larger value inductors allow more charge to be
transferred to the output per pulse, which increases both
efficiency and output voltage ripple. This dependence on
inductance is stronger for the LT8610AB than it is for the
LT8610A. If higher efficiency is needed in a Burst Mode ap-
plication, increasing inductor value can be a quick solution.
Table 1. Output Voltage Ripple vs Output Capacitance for
LT8610AB when VIN = 12V, VOUT = 3.3V, and L = 4.7µH
OUTPUT CAPACITANCE OUTPUT RIPPLE
47µF 40mV
47µF ×220mV
47µF ×410mV
For some applications it is desirable for the LT8610A/
LT8610AB to operate 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 (see Figure 1b). To enable
pulse-skipping mode, the SYNC pin is tied high either to a
logic output or to the INTVCC pin. When a clock is applied
to the SYNC pin the LT8610A/LT8610AB will also operate
in pulse-skipping mode.
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 VOUT
0.970V –1
(1)
Reference designators refer to the Block Diagram. 1%
resistors are recommended to maintain output voltage
accuracy.
When using large FB resistors, a 4.7pF to 10pF phase-lead
capacitor should be connected from VOUT to FB.
The fixed output versions of the LT8610A/LT8610AB
series have the feedback resistor network and phase
lead capacitor integrated within the part. The FB pin is
replaced with a VOUT pin for these regulators. The VOUT
pin can be connected directly to the inductor and output
capacitor. The 3.3V fixed output products (LT8610A-3.3/
LT8610AB-3.3) have a total of 14.3M of internal feedback
divider resistance from the VOUT pin to ground. The 5V
fixed output products (LT8610A-5/LT8610AB-5) have a
total of 12.5M of internal feedback divider resistance from
the VOUT pin to ground.
If low input quiescent current and good light-load efficiency
are desired, use large resistor values for the FB resistor
divider. The current flowing in the divider acts as a load
current, and will increase the no-load input current to the
converter, which is approximately:
IQ=1.7µA +VOUT
R1+R2
VOUT
VIN
1
n
(2)
where 1.7µA is the quiescent current of the LT8610A/
LT8610AB and the second term is the current in the feed-
back divider reflected to the input of the buck operating at
its light load efficiency n. For a 3.3V application with R1
= 1M and R2 = 412k, the feedback divider draws 2.3µA.
With VIN = 12V and n = 80%, this adds 0.8µA to the 1.7µA
quiescent current resulting in 2.5µA no-load current from
the 12V supply. Note that this equation implies that the
no-load current is a function of VIN; this is plotted in the
Typical Performance Characteristics section.
Setting the Switching Frequency
The LT8610A/LT8610AB uses a constant frequency PWM
architecture 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 RT value for
a desired switching frequency is in Table 1.
The RT resistor required for a desired switching frequency
can be calculated using:
RT=
46.5
f
SW
– 5.2
(3)
LT8610A/LT8610AB Series
15
8610abfa
For more information www.linear.com/LT8610A
APPLICATIONS INFORMATION
where RT is in kΩ and fSW is the desired switching fre-
quency in MHz.
Table 1. SW Frequency vs RT Value
fSW (MHz) RT (kΩ)
0.2 232
0.3 150
0.4 110
0.5 88.7
0.6 71.5
0.7 60.4
0.8 52.3
1.0 41.2
1.2 33.2
14 28.0
1.6 23.7
1.8 20.5
2.0 18.2
2.2 15.8
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 induc-
tor and capacitor values may be used. The disadvantages
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) =
V
OUT
+V
SW(BOT)
tON(MIN) VIN – VSW(TOP) +VSW(BOT)
( )
(4)
where VIN is the typical input voltage, VOUT is the output
voltage, VSW(TOP) and VSW(BOT) are the internal switch
drops (~0.42V, ~0.21V, respectively at maximum load)
and tON(MIN) is the minimum top switch on-time (see the
Electrical Characteristics). This equation shows that a
slower switching frequency is necessary to accommodate
a high VIN/VOUT ratio.
For transient operation, VIN may go as high as the abso-
lute maximum rating of 42V regardless of the RT value,
however the LT8610A/LT8610AB will reduce switching
frequency as necessary to maintain control of inductor
current to assure safe operation.
The LT8610A/LT8610AB is capable of a maximum duty
cycle of greater than 99%, and the VIN-to-VOUT dropout
is limited by the RDS(ON) of the top switch. In this mode
the LT8610A/LT8610AB 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) =
V
OUT
+V
SW(BOT)
1– fSW • tOFF(MIN)
– VSW(BOT) +VSW(TOP)
(5)
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 (~0.42V, ~0.21V,
respectively at maximum load), fSW is the switching fre-
quency (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.
Inductor Selection and Maximum Output Current
The LT8610A/LT8610AB is designed to minimize solution
size by allowing the inductor to be chosen based on the
output load requirements of the application. During over-
load or short-circuit conditions the LT8610A/LT8610AB
safely tolerates operation 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)
fSW
(6)
where fSW is the switching frequency in MHz, VOUT is
the output voltage, VSW(BOT) is the bottom switch drop
(~0.21V) 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 application. 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:
I
L(PEAK) =ILOAD(MAX) +
1
2
∆IL
(7)
LT8610A/LT8610AB Series
16
8610abfa
For more information www.linear.com/LT8610A
APPLICATIONS INFORMATION
where ∆IL is the inductor ripple current as calculated in
Equation 9 and ILOAD(MAX) is the maximum output load
for a given application.
As a quick example, an application requiring 1A output
should use an inductor with an RMS rating of greater than
1A and an ISAT of greater than 1.3A. During long duration
overload or short-circuit conditons, the inductor RMS
routing requirement is greater to avoid overheating of the
inductor. 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 LT8610A/LT8610AB 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 6A at low duty cycles and decreases linearly to 5A
at DC = 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 –
∆I
L
2
(8)
The peak-to-peak ripple current in the inductor can be
calculated as follows:
∆IL=VOUT
L • fSW
• 1– VOUT
VIN(MAX)
(9)
where fSW is the switching frequency of the LT8610A/
LT8610AB, and L is the value of the inductor. Therefore,
the maximum output current that the LT8610A/LT8610AB
will deliver depends on the switch current limit, the induc-
tor value, and the input and output voltages. The inductor
value may have to be increased if the inductor ripple cur-
rent 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
requiring smaller load currents, the value of the inductor
may be lower and the LT8610A/LT8610AB 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.
Inductor value has a very strong effect on Burst Mode ef-
ficiency. Larger value inductors allow more charge to be
transferred to the output per pulse, which increases both
efficiency and output voltage ripple. This dependence on
inductance is stronger for the LT8610AB than it is for the
LT8610A. If higher efficiency is needed in a Burst Mode ap-
plication, increasing inductor value can be a quick solution.
For more information about maximum output current
and discontinuous operation, see Linear Technology’s
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 Application Note 19.
Input Capacitor
Bypass the input of the LT8610A/LT8610AB circuit with a
ceramic capacitor of X7R or X5R type placed as close as
possible to the VIN and PGND pins. Y5V types have poor
performance over temperature and applied voltage, and
should not be used. A 4.7μF to 10μF ceramic capacitor
is adequate to bypass the LT8610A/LT8610AB and will
easily handle the ripple 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 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 supply in
pulses with very fast rise and fall times. The input capaci-
tor is required to reduce the resulting voltage ripple at the
LT8610A/LT8610AB 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 LT8610A/LT8610AB (see the PCB Layout
section). A second precaution regarding the ceramic input
capacitor concerns the maximum input voltage rating of the
LT8610A/LT8610AB. A ceramic input capacitor combined
LT8610A/LT8610AB Series
17
8610abfa
For more information www.linear.com/LT8610A
APPLICATIONS INFORMATION
with trace or cable inductance forms a high quality (under
damped) tank circuit. If the LT8610A/LT8610AB circuit is
plugged into a live supply, the input voltage can ring to
twice its nominal value, possibly exceeding the LT8610A/
LT8610AB’s voltage rating. This situation is easily avoided
(see Linear Technology 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 LT8610A/LT8610AB 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
stabilize the LT8610A/LT8610AB’s control loop. Ceramic
capacitors have very low equivalent series resistance (ESR)
and provide the best ripple performance. For good starting
values, see the Typical Applications section.
Use X5R or X7R types. This choice will provide low output
ripple and good transient 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
performance 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 capacitance
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 LT8610A/LT8610AB due to their
piezoelectric nature. When in Burst Mode operation, the
LT8610A/LT8610AB’s switching frequency depends on
the load current, and at very light loads the LT8610A/
LT8610AB can excite the ceramic capacitor at audio fre-
quencies, generating audible noise. Since the LT8610A/
LT8610AB operates at a lower current limit during Burst
Mode operation, the noise is typically very quiet to a ca-
sual ear. If this is unacceptable, use a high performance
tantalum or electrolytic capacitor at the output. Low noise
ceramic capacitors are also available.
A final precaution regarding ceramic capacitors concerns the
maximum input voltage rating of the LT8610A/LT8610AB. As
previously mentioned, a ceramic input capacitor combined
with trace or cable inductance forms a high quality (un-
derdamped) tank circuit. If the LT8610A/LT8610AB circuit
is plugged into a live supply, the input voltage can ring to
twice its nominal value, possibly exceeding the LT8610A/
LT8610AB’s rating. This situation is easily avoided (see
Linear Technology Application Note 88).
Enable Pin
The LT8610A/LT8610AB is in shutdown when the EN pin
is low and active when the pin is high. The rising threshold
of the EN comparator is 1.0V, with 40mV 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 VIN to EN programs the
LT8610A/LT8610AB to regulate the output only when VIN
is above a desired voltage (see the Block Diagram). Typi-
cally, this threshold, VIN(EN), is used in situations where
the input 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
VIN(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
•1.0V
(10)
where the LT8610A/LT8610AB will remain off until VIN is
above VIN(EN). Due to the comparator’s hysteresis, switch-
ing will not stop until the input falls slightly below VIN(EN).
LT8610A/LT8610AB Series
18
8610abfa
For more information www.linear.com/LT8610A
APPLICATIONS INFORMATION
When operating 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 LT8610A/LT8610AB. Therefore, the VIN(EN) resis-
tors should be large to minimize their effect on efficiency
at low loads.
INTVCC Regulator
An internal low dropout (LDO) regulator produces the 3.4V
supply from VIN that powers the drivers and the internal
bias circuitry. The INTVCC can supply enough current for
the LT8610A/LT8610AB’s circuitry and must be bypassed
to ground with a minimum of 1μF ceramic capacitor. Good
bypassing is necessary to supply the high transient currents
required by the power MOSFET gate drivers. To improve
efficiency the internal LDO can also draw current from the
BIAS pin when the BIAS pin is at 3.1V or higher. Typically
the BIAS pin can be tied to the output of the LT8610A/
LT8610AB, or can be tied to an external supply of 3.3V or
above. If BIAS is connected to a supply other than VOUT,
be sure to bypass with a local ceramic capacitor. If the
BIAS pin is below 3.0V, the internal LDO will consume
current from VIN. Applications with high input voltage and
high switching frequency where the internal LDO pulls
current from VIN 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
T
he LT8610A/LT8610AB allows the user to program its out-
put voltage ramp rate by means of the TR/SS pin. An internal
2.2μA 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
TR/SS pin voltage. For output tracking applications, TR/SS
can be externally driven by another voltage source. From
0V to 0.97V, the TR/SS voltage will override the internal
0.97V reference input to the error amplifier, thus regulating
the FB pin voltage to that of TR/SS pin. In the fixed output
voltage options the output voltage will track the TR/SS
pin voltage based on a factor set by the internal feedback
resistor divider. The 3.3V output options will track to a
voltage 3.4 times that of the TR/SS pin, while the 5V output
options will track to a voltage 5.15 times that of the TR/SS
pin. When TR/SS is above 0.97V, tracking is disabled and
the feedback voltage will regulate to the internal reference
voltage. The TR/SS pin may be left floating if the function
is not needed.
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.
Output Power Good
When the LT8610A/LT8610AB’s output voltage is within
the ±9% window of the regulation point, which is a VFB
voltage in the range of 0.883V to 1.057V (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 pull-down
device will pull the PG pin low. To prevent glitching both
the upper and lower thresholds include 1.3% of hysteresis.
This ±9% power good window around the regulation point
is the same for the fixed output options, which for the 3.3V
output version corresponds to a 3.003V to 3.597V range
(typical) and for the 5V output version corresponds to a
4.55V to 5.45V range (typical).
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
To select low ripple Burst Mode operation, tie the SYNC
pin below 0.4V (this can be ground or a logic low output).
To synchronize the LT8610A/LT8610AB oscillator to an
external frequency connect a square wave (with 20% to
80% duty cycle) to the SYNC pin. The square wave am-
plitude should have valleys that are below 0.4V and peaks
above 2.4V (up to 6V).
The LT8610A/LT8610AB will not enter Burst Mode opera-
tion at low output loads while synchronized to an external
clock, but instead will pulse skip to maintain regulation. The
LT8610A/LT8610AB may be synchronized over a 200kHz
LT8610A/LT8610AB Series
19
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For more information www.linear.com/LT8610A
APPLICATIONS INFORMATION
Figure 3. Reverse VIN Protection
VIN
V
IN
D1
LT8610A/
LT8610AB
EN/UV
8610ab F03
GND
to 2.2MHz range. The RT resistor should be chosen to set
the LT8610A/LT8610AB switching frequency equal to or
below the lowest synchronization input. For example, if the
synchronization signal will be 500kHz and higher, the RT
should be selected for 500kHz. The slope compensation is
set by the RT value, while the minimum slope compensation
required to avoid subharmonic oscillations is established
by the inductor size, input voltage, and output voltage.
Since the synchronization 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 RT, then the slope compensation will be
sufficient for all synchronization frequencies.
For some applications it is desirable for the LT8610A/
LT8610AB to operate 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. Second is that full switching frequency
is reached at lower output load than in Burst Mode operation.
These two differences come at the expense of increased
quiescent current. To enable pulse-skipping mode, the SYNC
pin is tied high either to a logic output or to the INTVCC pin.
The LT8610A/LT8610AB does not operate in forced con-
tinuous mode regardless of SYNC signal. Never leave the
SYNC pin floating.
Shorted and Reversed Input Protection
The LT8610A/LT8610AB 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 switch-
ing of the top switch will be delayed until such time as the
inductor current falls to safe levels.
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 or tied high, the LT8610A/LT8610AB 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 LT8610A/
LT8610AB 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 LT8610A/
LT8610AB’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 LT8610A/LT8610AB’s
internal circuitry will pull its quiescent current through
its SW pin. This is acceptable if the system can tolerate
several μA in this state. If the EN pin is grounded the SW
pin current will drop to near 1µA. However, if the VIN pin
is grounded while the output is held high, regardless of
EN, parasitic body diodes inside the LT8610A/LT8610AB
can pull current from the output through the SW pin and
the VIN pin. Figure 3 shows a connection of the VIN and
EN/UV pins that will allow the LT8610A/LT8610AB to run
only when the input voltage is present and that protects
against a shorted or reversed input.
PCB Layout
For proper operation and minimum EMI, care must be taken
during printed circuit board layout. Figure 4 shows the
recommended component placement with trace, ground
plane and via locations. Note that large, switched currents
flow in the LT8610A/LT8610AB’s VIN pins, GND pins, and
the input capacitor (C1). 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 preferred. 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
LT8610A/LT8610AB Series
20
8610abfa
For more information www.linear.com/LT8610A
Figure 4. Recommended PCB Layout for the LT8610A/LT8610AB
VOUT
8610ab F04
OUTLINE OF LOCAL
GROUND PLANE
SW
BST
BIAS
INTVCC
GND
9
10
11
12
13
14
15 PG
FB
GND
VOUT
16
SYNC
TR/SS
RT
EN/UV
VIN
1
2
3
4
5
6
7
8
VOUT LINE TO BIAS VIAS TO GROUND PLANE
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 the ground plane as much as possible, and
add thermal vias under and near the LT8610A/LT8610AB
to additional ground planes within the circuit board and
on the bottom side.
Unlike the LT8610, the LT8610A/LT8610AB has pin 7 as an
NC (no connect) pin. This pin can be soldered to GND to
have an LT8610 compatible PCB layout. Alternatively, pin 7
APPLICATIONS INFORMATION
can be left unconnected to help meet PCB clearance and
creepage requirements between the VIN and GND traces.
High Temperature Considerations
For higher ambient temperatures, care should be taken
in the layout of the PCB to ensure good heat sinking of
the LT8610A/LT8610AB. 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 layers will spread heat dissipated by
the LT8610A/LT8610AB. 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
LT8610A/LT8610AB can be estimated by calculating the
total power loss from an efficiency measurement and sub-
tracting the inductor loss. The die temperature is calculated
by multiplying the LT8610A/LT8610AB power dissipation
by the thermal resistance from junction to ambient. The
LT8610A/LT8610AB will stop switching and indicate a
fault condition if safe junction temperature is exceeded.
Temperature rise of the LT8610A/LT8610AB is worst
when operating at high load, high VIN, and high switching
frequency. If the case temperature is too high for a given
application, then either VIN, switching frequency, or load
current can be decreased to reduce the temperature to an
acceptable level. Figure 5 shows an example of how case
temperature can be managed by reducing VIN, switching
frequency, or load.
Figure 5. LT8610AB Case Temperature Rise
INPUT VOLTAGE (V)
CASE TEMPERATURE RISE (°C)
120
140
16 24
36
8610ab F05
80
20
40
0
100
60
8 12 20 28 32
fSW = 2MHz
ILOAD = 2.5A
fSW = 2MHz
ILOAD = 3.5A
TA = 25°C
fSW = 1MHz
ILOAD = 3.5A
LT8610A/LT8610AB Series
21
8610abfa
For more information www.linear.com/LT8610A
TYPICAL APPLICATIONS
BSTVIN
EN/UV
SYNC
INTVCC
TR/SS
RT
SW
LT8610A/
LT8610AB
GND
BIAS
8610ab TA02
PG
FB
0.1µF
V
OUT
5V
3.5A
4.7µF
V
IN
5.5V TO 42V
1µF
10nF
4.7pF
2.2µH
1M
243k
fSW = 2MHz
L: XAL 5030
18.2k
47µF*
1210
X7R
POWER GOOD
100k
5V 2MHz Step-Down Converter
5V Step-Down Converter
*Consider doubling output capacitance for LT8610AB if application requires low output voltage ripple in Burst Mode operation.
12V Step-Down Converter
L: IHLP-2525CZ-01
BSTVIN
EN/UV
SYNC
INTVCC
TR/SS
RT
SW
LT8610A-5
GND
BIAS
8610ab TA03
VOUT
0.1µF
V
OUT
12V
3.5A
4.7µF
V
IN
3.8V TO 42V
1µF
10nF
10µH
fSW = 400kHz
110k
100µF
1210
X5R
PG POWER GOOD
100k
BSTVIN
EN/UV
SYNC
INTVCC
TR/SS
RT
SW
LT8610A/
LT8610AB
GND
BIAS
8610ab TA09
PG
FB
0.1µF
V
OUT
12V
3.5A
4.7µF
V
IN
12.5V TO 42V
1µF
10nF
10pF
10µH
1M
88.7k
fSW = 1MHz
41.2k
47µF*
1210
X7R
POWER GOOD
100k
L: IHLP-2525CZ-01
LT8610A/LT8610AB Series
22
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For more information www.linear.com/LT8610A
TYPICAL APPLICATIONS
1.8V 2MHz Step-Down Converter
*Consider doubling output capacitance for LT8610AB if application requires low output voltage ripple in Burst Mode operation.
BSTVIN
EN/UV
SYNC
PG
INTVCC
TR/SS
RT
SW
LT8610A/
LT8610AB
GND
BIAS
8610ab TA06
FB
0.1µF
V
OUT
1.8V
3.5A
4.7µF
V
IN
3.4V TO 15V
(42V TRANSIENT)
1µF
10nF
4.7pF
1µH
866k
1M
fSW = 2MHz
18.2k
100µF*
1210
X5R
L: IHLP-2020BZ-01
3.3V 2MHz Step-Down Converter
BSTVIN
EN/UV
SYNC
PG
INTVCC
TR/SS
RT
SW
LT8610A/
LT8610AB
GND
BIAS
8610ab TA04
FB
0.1µF
V
OUT
3.3V
3.5A
4.7µF
V
IN
3.8V TO 27V
(42V TRANSIENT)
1µF
10nF
4.7pF
2.2µH
1M
412k
fSW = 2MHz
18.2k
47µF*
1210
X7R
L: XAL 5030
1.8V Step-Down Converter
BSTVIN
EN/UV
SYNC
PG
INTVCC
TR/SS
RT
SW
LT8610A/
LT8610AB
GND
BIAS
8610ab TA07
FB
0.1µF
V
OUT
1.8V
3.5A
4.7µF
V
IN
3.4V TO 42V
1µF
10nF
4.7pF
4.7µH
866k
1M
fSW = 400kHz
110k
47µF*
×3
1210
X7R
L: IHLP-2020BZ-01
LT8610A/LT8610AB Series
23
8610abfa
For more information www.linear.com/LT8610A
TYPICAL APPLICATIONS
3.3V Step-Down Converter
Ultralow EMI 5V 2.5A Step-Down Converter
L: IHLP-2525BD-01
BSTVIN
EN/UV
PG
SYNC
INTVCC
TR/SS
RT
SW
LT8610A-3.3
GND
BIAS
8610ab TA05
VOUT
0.1µF
V
OUT
3.3V
3.5A
4.7µF
V
IN
3.8V TO 42V
1µF
10nF
8.2µH
fSW = 400kHz
110k
100µF
1210
X5R
BSTVIN
EN/UV
PG
SYNC
INTVCC
TR/SS
RT
SW
LT8610A/
LT8610AB
GND
BIAS
8610ab TA11
FB
0.1µF
V
OUT
5V
3.5A
4.7µF
VIN
5.5V TO 42V
1µF
10nF
10pF
4.7µH
4.7µH
1M
FB1
BEAD
243k
fSW = 800kHz
52.3k
4.7µF4.7µF
47µF*
1210
X7R
FB1: TDK MPZ2012S101A
L: IHLP-2020BZ-01
*Consider doubling output capacitance for LT8610AB if application requires low output voltage ripple in Burst Mode operation.
LT8610A/LT8610AB Series
24
8610abfa
For more information www.linear.com/LT8610A
PACKAGE DESCRIPTION
Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings.
MSOP (MSE16) 0213 REV F
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
16
161514 13121110
12345678
9
9
18
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
0.305 ±0.038
(.0120
±.0015)
TYP
0.50
(.0197)
BSC
BOTTOM VIEW OF
EXPOSED PAD OPTION
2.845 ±0.102
(.112 ±.004)
2.845 ±0.102
(.112 ±.004)
4.039 ±0.102
(.159 ±.004)
(NOTE 3)
1.651 ±0.102
(.065 ±.004)
1.651 ±0.102
(.065 ±.004)
0.1016 ±0.0508
(.004 ±.002)
3.00 ±0.102
(.118 ±.004)
(NOTE 4)
0.280 ±0.076
(.011 ±.003)
REF
4.90 ±0.152
(.193 ±.006)
DETAIL “B”
DETAIL “B”
CORNER TAIL IS PART OF
THE LEADFRAME FEATURE.
FOR REFERENCE ONLY
NO MEASUREMENT PURPOSE
0.12 REF
0.35
REF
MSE Package
16-Lead Plastic MSOP, Exposed Die Pad
(Reference LTC DWG # 05-08-1667 Rev F)
LT8610A/LT8610AB Series
25
8610abfa
For more information www.linear.com/LT8610A
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 08/14 Added fixed output options.
Clarified Applications Information.
1 - 4, 10, 12, 13
14, 18
LT8610A/LT8610AB Series
26
8610abfa
For more information www.linear.com/LT8610A
LINEAR TECHNOLOGY CORPORATION 2013
LT 0814 REV A • PRINTED IN USA
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com/LT8610A
RELATED PARTS
TYPICAL APPLICATION
3.3V and 1.8V with Ratio Tracking Ultralow IQ 2.5V, 3.3V Step-Down with LDO
BSTVIN
EN/UV
SYNC
PG
INTVCC
TR/SS
RT
SW
LT8610A/
LT8610AB
GND
BIAS
FB
0.1µF
V
OUT1
3.3V
3.5A
4.7µF
V
IN
3.8V TO 42V
1µF
10nF
4.7pF
5.6µH
232k
97.6k
fSW = 500kHz
88.7k
BSTVIN
EN/UV
SYNC
PG
INTVCC
TR/SS
RT
SW
LT8610A/
LT8610AB
GND
BIAS
8610ab TA08
FB
0.1µF
V
OUT2
1.8V
3.5A
4.7µF
1µF
4.7pF
3.3µH
80.6k
24.3k
93.1k
fSW = 500kHz
88.7k
10k
100µF*
1210
X5R
47µF*
1210
X7R
L: IHLP-2020CZ-01, 5.6µH
L: IHLP-2020CZ-01, 3.3µH
BSTVIN
EN/UV
SYNC
PG
INTVCC
TR/SS
RT
SW
LT8610AB-3.3
GND
BIAS
8610ab TA10
VOUT
0.1µF
VOUT1
3.3V
3.5A
4.7µF
V
IN
3.8V TO 27V
1µF
10nF
2.2µH
2.2µF
V
OUT2
2.5V
20mA
fSW = 2MHz
18.2k
47µF
×2
1210
X7R
IN
LT3008-2.5
SHDN
OUT
SENSE
L: IHLP-2020BZ-01
PART NUMBER DESCRIPTION COMMENTS
LT8610 42V, 2.5A, 96% Efficiency, 2.2MHz Synchronous Micropower Step-Down
DC/DC Converter with IQ = 2.5µA
VIN: 3.4V to 42V, VOUT(MIN) = 0.97V, IQ = 2.5µA,
ISD < 1µA, MSOP-16E Package
LT8614 42V, 2.5A with 4A, 96% Efficiency, 2.2MHz Synchronous Micropower
Step-Down DC/DC Converter with IQ = 2.5µA
VIN: 3.4V to 42V, VOUT(MIN) = 0.97V, IQ = 2.5µA,
ISD < 1µA, 3mm × 6mm QFN-28 Package
LT8611 42V, 2.5A, 96% Efficiency, 2.2MHz Synchronous Micropower Step-Down
DC/DC Converter with IQ = 2.5µA and Input/Output Current Limit/Monitor
VIN: 3.4V to 42V, VOUT(MIN) = 0.97V, IQ = 2.5µA,
ISD < 1µA, 3mm × 5mm QFN-24 Package
LT3690 36V with 60V Transient Protection, 4A, 92% Efficiency, 1.5MHz
Synchronous Micropower Step-Down DC/DC Converter with IQ = 70µA
VIN: 3.9V to 36V, VOUT(MIN) = 0.985V, IQ = 70µA,
ISD < 1µA, 4mm × 6mm QFN-26 Package
LT3971 38V, 1.2A, 2.2MHz High Efficiency Micropower Step-Down DC/DC
Converter with IQ = 2.8µA
VIN: 4.2V to 38V, VOUT(MIN) = 1.21V, IQ = 2.8µA,
ISD < 1µA, 3mm × 3mm DFN-10 and MSOP-10E Packages
LT3970 40V, 350mA, 2.2MHz High Efficiency Micropower Step-Down DC/DC
Converter with IQ = 2.5µA
VIN: 4.2V to 40V, VOUT(MIN) = 1.21V, IQ = 2.5µA,
ISD < 1µA, 3mm × 2mm DFN-10 and MSOP-10 Packages
LT3990 62V, 350mA, 2.2MHz High Efficiency MicroPower Step-Down DC/DC
Converter with IQ = 2.5µA
VIN: 4.2V to 62V, VOUT(MIN) = 1.21V, IQ = 2.5µA,
ISD < 1µA, 3mm × 3mm DFN-10 and MSOP-6E Packages
LT3480 36V with Transient Protection to 60V, 2A (IOUT), 2.4MHz, High Efficiency
Step-Down DC/DC Converter with Burst Mode Operation
VIN: 3.6V to 36V, Transient to 60V, VOUT(MIN) = 0.78V,
IQ = 70µA, ISD < 1µA, 3mm × 3mm DFN-10 and
MSOP-10E Packages
LT3980 58V with T
ransient Protection to 80V, 2A (IOUT), 2.4MHz, High Efficiency
Step-Down DC/DC Converter with Burst Mode Operation
VIN: 3.6V to 58V, Transient to 80V, VOUT(MIN) = 0.78V,
IQ = 85µA, ISD < 1µA, 3mm × 4mm DFN-16 and
MSOP-16E Packages
*Consider doubling output capacitance for LT8610AB if application requires low output voltage ripple in Burst Mode operation.
