LT8610A/LT8610AB Series
42V, 3.5A Synchronous
Step-Down Regulator with
2.5µA Quiescent Current
FEATURES
DESCRIPTION
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 < 10mV
P-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
The LT®8610A/LT8610AB series are compact, high efficiency, high speed synchronous monolithic step-down
switching regulators that consume only 2.5µA of quiescent 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.
n
APPLICATIONS
The other features of the LT8610 remain unchanged in the
LT8610A/LT8610AB series. A SYNC pin allows synchronization 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
Automotive and Industrial Supplies
GSM Power Supplies
n
L, LT, LTC, LTM, 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.
n
TYPICAL APPLICATION
LT8610AB Efficiency at 5VOUT
5V 3.5A Step-Down Converter
4.7µF
10nF
1µF
VIN
BST
EN/UV
LT8610AB-5
SW
PG
SYNC
BIAS
TR/SS
VOUT
INTVCC
RT
0.1µF
4.7µH
90
VOUT
5V
47µF 3.5A
×2
80
EFFICIENCY (%)
VIN
5.5V TO 42V
100
70
60
50
GND
VIN = 12V
VIN = 24V
VIN = 36V
40
60.4k
fSW = 700kHz
30
0.1
8610ab TA01a
1
10
100
1000
LOAD CURRENT (mA)
8610ab TA01b
8610abfa
For more information www.linear.com/LT8610A
1
LT8610A/LT8610AB Series
ABSOLUTE MAXIMUM RATINGS
(Note 1)
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
PIN CONFIGURATION
LT8610A, LT8610AB
LT8610A-3.3, LT8610A-5, LT8610AB-3.3, LT8610AB-5
TOP VIEW
SYNC
TR/SS
RT
EN/UV
VIN
VIN
NC
GND
1
2
3
4
5
6
7
8
17
GND
TOP VIEW
16
15
14
13
12
11
10
9
FB
PG
BIAS
INTVCC
BST
SW
SW
SW
SYNC
TR/SS
RT
EN/UV
VIN
VIN
NC
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
17
GND
16
15
14
13
12
11
10
9
VOUT
PG
BIAS
INTVCC
BST
SW
SW
SW
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
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 LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container.
Consult LTC 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/
8610abfa
2
For more information www.linear.com/LT8610A
LT8610A/LT8610AB Series
ELECTRICAL
CHARACTERISTICS
The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C.
PARAMETER
CONDITIONS
Minimum Input Voltage
(Note 4)
VIN Quiescent Current
VEN/UV = 0V
MIN
TYP
MAX
l
2.9
3.4
V
l
1.0
1.0
3
8
µA
µA
l
1.7
1.7
4
10
µA
µA
VEN/UV = 2V, Not Switching, VSYNC = 0V
VEN/UV = 2V, Not Switching, VSYNC = 2V
UNITS
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
l
0.004
0.02
%/V
Voltage Line Regulation
(LT8610A-3.3/LT8610AB-3.3)
VIN = 4V to 42V, ILOAD = 1A
l
0.004
0.02
%/V
Voltage Line Regulation
(LT8610A-5/LT8610AB-5)
VIN = 6V to 42V, ILOAD = 1A
l
0.004
0.02
%/V
Feedback Pin Input Current
(LT8610A/LT8610AB)
VFB = 1V
20
nA
–20
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
INTVCC Undervoltage Lockout
BIAS Pin Current Consumption
VBIAS = 3.3V, ILOAD = 1A, 2MHz
Minimum On-Time
ILOAD = 1A, SYNC = 0V
ILOAD = 1A, SYNC = 3.3V
Minimum Off-Time
3.23
3.25
3.4
3.29
3.57
3.35
2.5
2.6
2.7
9
l
l
15
15
V
V
V
mA
30
30
45
45
ns
ns
95
125
ns
8610abfa
For more information www.linear.com/LT8610A
3
LT8610A/LT8610AB Series
ELECTRICAL
CHARACTERISTICS
The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C.
PARAMETER
CONDITIONS
Oscillator Frequency
RT = 221k, ILOAD = 1A
RT = 60.4k, ILOAD = 1A
RT = 18.2k, ILOAD = 1A
Top Power NMOS On-Resistance
ISW = 1A
Top Power NMOS Current Limit
LT8610A
LT8610AB
l
l
l
MIN
TYP
MAX
UNITS
180
665
1.85
210
700
2.00
240
735
2.15
kHz
kHz
MHz
120
l
l
5
5
Bottom Power NMOS On-Resistance VINTVCC = 3.4V, ISW = 1A
8
8
65
Bottom Power NMOS Current Limit
VINTVCC = 3.4V
3.4
SW Leakage Current
VIN = 42V, VSW = 0V, 42V
–1.5
EN/UV Pin Threshold
EN/UV Rising
l
0.94
EN/UV Pin Hysteresis
4.3
1.0
VEN/UV = 2V
–20
PG Upper Threshold Offset from VFB
VFB Falling
l
6
PG Lower Threshold Offset from VFB
VFB Rising
l
–12
PG Hysteresis
A
A
mΩ
5.4
A
1.5
µA
1.06
40
EN/UV Pin Current
V
mV
20
nA
9.0
12
%
–9.0
–6
%
40
nA
680
2000
Ω
1.1
2.0
1.4
2.4
V
V
40
nA
2.0
3.2
µA
1.3
PG Leakage
VPG = 3.3V
PG Pull-Down Resistance
VPG = 0.1V
SYNC Threshold
SYNC Falling
SYNC Rising
SYNC Pin Current
VSYNC = 6V
–40
l
0.8
1.6
–40
TR/SS Source Current
TR/SS Pull-Down Resistance
6.7
6.7
mΩ
l
Fault Condition, TR/SS = 0.1V
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.
1.0
%
230
Ω
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.
8610abfa
4
For more information www.linear.com/LT8610A
LT8610A/LT8610AB Series
TYPICAL PERFORMANCE CHARACTERISTICS
LT8610AB Efficiency at 5VOUT
100
95
90
fSW = 700kHz
L = IHLP-2020BZ-01, 4.7µH
70
65
70
fSW = 700kHz
L = IHLP-2020BZ-01, 4.7µH
60
50
VIN = 12V
VIN = 24V
VIN = 36V
55
0
0.5
1.5
2
2.5
1
LOAD CURRENT (A)
3
20
0.01
3.5
0.1
1
10
100
LOAD CURRENT (mA)
LT8610AB Efficiency at 3.3VOUT
100
65
60
50
1000
50
EFFICIENCY (%)
80
fSW = 700kHz
L = IHLP-2020BZ-01, 4.7µH
40
LT8610A Efficiency at 5VOUT
20
0.01
0.1
1
10
100
LOAD CURRENT (mA)
100
80
75
fSW = 700kHz
L = IHLP-2020BZ-01, 4.7µH
70
65
50
100
100
90
0
0.5
1.5
2
2.5
1
LOAD CURRENT (A)
3
65
VIN = 12V
VIN = 24V
VIN = 36V
55
0
0.5
1.5
2
2.5
1
LOAD CURRENT (A)
3
3.5
8610ab G44
VIN = 12V
VIN = 24V
VIN = 36V
0.1
1
10
100
LOAD CURRENT (mA)
100
VOUT = 3.3V
95 L = IHLP-2020BZ-01, 4.7µH
90
70
60
50
85
80
75
70
VIN = 12V
VIN = 24V
VIN = 36V
30
20
0.01
1000
LT8610A/LT8610AB
Efficiency vs Frequency at 1A
LT8610A Efficiency at 3.3VOUT
40
60
50
8610ab G43
EFFICIENCY (%)
70
EFFICIENCY (%)
fSW = 700kHz
L = IHLP-2020BZ-01, 4.7µH
fSW = 700kHz
L = IHLP-2020BZ-01, 4.7µH
60
20
0.01
3.5
80
75
70
30
fSW = 700kHz
90 L = IHLP-2020BZ-01, 4.7µH
95
3.5
LT8610A Efficiency at 5VOUT
8610ab G42
LT8610A Efficiency at 3.3VOUT
3
40
VIN = 12V
VIN = 24V
VIN = 36V
8610ab G04
80
1.5
2
2.5
1
LOAD CURRENT (A)
80
85
55
1000
85
0.5
90
60
VIN = 12V
VIN = 24V
VIN = 36V
30
0
8610ab G02
90
60
VIN = 12V
VIN = 24V
VIN = 36V
55
95
70
fSW = 700kHz
L = IHLP-2020BZ-01, 4.7µH
70
8610ab G03
90
EFFICIENCY (%)
75
VIN = 12V
VIN = 24V
VIN = 36V
30
8610ab G01
EFFICIENCY (%)
80
40
60
50
85
EFFICIENCY (%)
75
EFFICIENCY (%)
EFFICIENCY (%)
80
LT8610AB Efficiency at 3.3VOUT
95
80
85
100
100
90
90
50
LT8610AB Efficiency at 5VOUT
EFFICIENCY (%)
100
0.1
1
10
100
LOAD CURRENT (mA)
1000
8610ab G45
65
VIN = 12V
VIN = 24V
60
0.25 0.50 0.75 1.00 1.25 1.50 1.75 2.00 2.25
SWITCHING FREQUENCY (MHz)
8610ab G05
8610abfa
For more information www.linear.com/LT8610A
5
LT8610A/LT8610AB Series
TYPICAL PERFORMANCE CHARACTERISTICS
Reference Voltage
LT8610A-3.3 Output Voltage
0.979
OUTPUT VOLTAGE (V)
0.976
0.973
0.970
0.967
0.964
0.961
5.100
3.345
5.075
3.330
5.050
3.315
3.300
3.285
3.270
3.255
0.958
0.955
–55
65
35
5
95
TEMPERATURE (°C)
–25
125
65
35
5
95
TEMPERATURE (°C)
–25
8610ab G06
EN Pin Thresholds
125
155
4.900
–55
0.98
0.97
EN FALLING
0.96
0.95
–55
–25
5
35
65
95
TEMPERATURE (°C)
125
155
0.05
0
–0.05
–0.10
0
–0.03
–0.06
–0.20
–0.12
0
0.5
1.5
2
2.5
1
LOAD CURRENT (A)
3
3.5
–0.15
5.0
TESTED IN REGULATION
8610AB: VOUT = 3.3V
4.5
INPUT CURRENT (µA)
8610A
2.5 8610A-5
2.0
8610A-3.3
1.5
20
3.5
3.0
1.5
0.5
0.5
10
15 20 25 30
INPUT VOLTAGE (V)
35
40
8610ab G10
8610AB-5
2.0
1.0
5
8610AB
2.5
1.0
0
15 20 25 30 35
INPUT VOLTAGE (V)
0
40
45
No Load Supply Current
25
4.0
3.0
10
8610ab G09
LT8610AB No Load
Supply Current
4.0
3.5
5
0
8610ab G08
TESTED IN REGULATION
8610A: VOUT = 3.3V
4.5
0.03
–0.09
8610ab G07
5.0
0.06
–0.15
LT8610A No Load Supply Current
155
0.09
0.10
–0.25
125
VOUT = 3.3V
ILOAD = 0.5A
0.12
CHANGE IN VOUT (%)
CHANGE IN VOUT (%)
0.99
35
5
65
95
TEMPERATURE (°C)
Line Regulation
0.15
0.15
EN RISING
–25
8610ab G47
VOUT = 3.3V
VIN = 12V
0.20
1.00
EN THRESHOLD (V)
4.950
Load Regulation
0.25
1.01
INPUT CURRENT (µA)
4.975
8610ab G46
1.02
0
5.000
4.925
3.240
–55
155
5.025
INPUT CURRENT (µA)
REFERENCE VOLTAGE (V)
0.982
LT8610AB-3.3 Output Voltage
3.360
OUTPUT VOLTAGE (V)
0.985
8610AB-3.3
VOUT = 3.3V
VIN = 12V
IN REGULATION
15
10
5
0
5
10
15 20 25 30
INPUT VOLTAGE (V)
35
40
8610ab G48
0
–55
–25
65
5
95
35
TEMPERATURE (°C)
125
155
8610ab G11
8610abfa
6
For more information www.linear.com/LT8610A
LT8610A/LT8610AB Series
TYPICAL PERFORMANCE CHARACTERISTICS
Top FET Current Limit
5.50
7.5
6.75
5.25
7.0
6.50
6.5
6.25
5.5
5.0
4.5
5.00
30% DC
CURRENT LIMIT (A)
6.0
6.00
5.75
5.50
5.25
4.50
4.25
4.00
3.75
5.00
3.50
3.5
4.75
3.25
0.4
0.6
DUTY CYCLE
0.8
4.50
–55
1.0
–25
5
35
65
TEMPERATURE (°C)
–55
Switch Drop
SWITCH DROP (mV)
200
150
TOP SW
BOT SW
65
5
95
35
TEMPERATURE (°C)
125
400
ILOAD = 1.5A
43 VSYNC = 0V
350
41
300
250
TOP SW
200
BOT SW
150
0
155
110
105
100
95
90
85
0
0.5
1
1.5
2
SWITCH CURRENT (A)
31
25
–55
3
2.5
125
155
8610ab G18
VOUT = 3.3V
VOUT = 0.97V
–25
5
65
95
35
TEMPERATURE (°C)
155
Switching Frequency
740
700
730
600
500
400
300
200
0
125
8610ab G17
800
RT = 60.4k
720
710
700
690
680
670
100
80
95
65
35
TEMPERATURE (°C)
33
27
SWITCHING FREQUENCY (kHz)
DROPOUT VOLTAGE (V)
115
5
35
Dropout Voltage
VOUT = 3.3V
ILOAD = 0.5A
75
–50 –25
37
8610ab G41
Minimum Off-Time
120
39
29
8610ab G40
125
155
Minimum On-Time
50
–25
125
45
100
50
0
–55
95
5
35
65
TEMPERATURE (°C)
–25
8610ab G15
450
SWITCH CURRENT = 1A
100
3.00
125
8610ab G14
Switch Drop
250
95
MINIMUM ON-TIME (ns)
0.2
0
8610ab G13
MINIMUM OFF-TIME (ns)
4.75
4.0
3.0
SWITCH DROP (mV)
Bottom FET Current Limit
7.00
CURRENT LIMIT (A)
CURRENT LIMIT (A)
Top FET Current Limit vs Duty Cycle
8.0
0
0.5
1.5
2
2.5
1
LOAD CURRENT (A)
3
3.5
8610ab G19
660
–55 –25
95
65
35
TEMPERATURE (°C)
5
125
155
8610ab G20
8610abfa
For more information www.linear.com/LT8610A
7
LT8610A/LT8610AB Series
TYPICAL PERFORMANCE CHARACTERISTICS
Minimum Load to Full Frequency
700
70
600
LT8610A
500
LT8610AB
400
300
200
VIN = 12V
VOUT = 3.3V
L = 4.7µH
100
0
0
VOUT = 3.3V
fSW = 700kHz
PULSE-SKIPPING MODE
60
50
40
30
20
10
0
100 200 300 400 500 600 700 800
LOAD CURRENT (mA)
5
10
20
15
25
30
INPUT VOLTAGE (V)
SS PIN CURRENT (µA)
FB VOLTAGE (V)
1.0
0.6
0.4
0.2
1.2
VSS = 0.5V
2.2
2.1
2.0
1.9
1.8
1.6
–50 –25
1.4
250
–7.5
225
–8.0
200
95
65
35
TEMPERATURE (°C)
5
125
–10.0
FB FALLING
–10.5
9.5
125
155
8610ab G26
FB FALLING
9.0
8.5
8.0
7.5
65
35
5
95
TEMPERATURE (°C)
–25
75
0
0.2
125
155
8610ab G25
3.2
100
25
65
35
5
95
TEMPERATURE (°C)
FB RISING
10.0
3.4
125
–11.5
–25
10.5
VIN UVLO
150
50
–12.0
–55
11.0
3.6
175
–11.0
1
11.5
7.0
–55
155
INPUT VOLTAGE (V)
RT PIN RESISTOR (kΩ)
PG THRESHOLD OFFSET FROM VREF (%)
–7.0
0.8
8610ab G22
RT Programmed Switching
Frequency
FB RISING
0.4
0.6
FB VOLTAGE (V)
8610ab G24
PG Low Thresholds
–8.5
0.2
0
PG High Thresholds
8610ab G23
–9.5
200
12.0
1.7
–9.0
300
0
40
35
2.3
1.0
0.4 0.6 0.8
TR/SS VOLTAGE (V)
400
Soft-Start Current
2.4
0.2
500
100
PG THRESHOLD OFFSET FROM VREF (%)
Soft-Start Tracking
0
600
8610ab G39
1.2
0.8
VOUT = 3.3V
VIN = 12V
VSYNC = 0V
RT = 60.4k
700
8610ab G21
0
Frequency Foldback
800
SWITCHING FREQUENCY (kHz)
80
LOAD CURRENT (mA)
SWITCHING FREQUENCY (kHz)
Burst Frequency
800
3.0
2.8
2.6
2.4
2.2
0.6
1.4
1.8
1
SWITCHING FREQUENCY (MHz)
2.2
8610ab G27
2.0
–55 –25
95
65
35
TEMPERATURE (°C)
5
125
155
8610ab G28
8610abfa
8
For more information www.linear.com/LT8610A
LT8610A/LT8610AB Series
TYPICAL PERFORMANCE CHARACTERISTICS
Bias Pin Current
6.5
VBIAS = 5V
VOUT = 5V
ILOAD = 1A
fSW = 700kHz
5.5
5.0
4.5
4.0
3.5
IL
1A/DIV
8
VSW
5V/DIV
6
4
500ns/DIV
12VIN TO 5VOUT AT 1A
2
3.0
2.5
Switching Waveforms
VBIAS = 5V
VOUT = 5V
VIN = 12V
ILOAD = 1A
10
BIAS PIN CURRENT (mA)
6.0
BIAS PIN CURRENT (mA)
Bias Pin Current
12
5
10
15
20 25 30 35
INPUT VOLTAGE (V)
40
45
0
0
2.5
0.5
1
1.5
2
SWITCHING FREQUENCY (MHz)
8610ab G30
8610ab G29
Switching Waveforms
LT8610A/LT8610AB
Transient Response
Switching Waveforms
IL
200mA/DIV
IL
1A/DIV
VOUT
200mV/DIV
VSW
10V/DIV
VSW
5V/DIV
500µs/DIV
12VIN TO 5VOUT AT 10mA
VSYNC = 0V
(LT8610A)
LT8610A/LT8610AB
Transient Response
50µs/DIV
1.5A TO 3.5A TRANSIENT
12VIN, 3.3VOUT
COUT = 47µF
8610ab G33
Start-Up Dropout Performance
VIN
2V/DIV
VOUT
2V/DIV
IL
2A/DIV
50µs/DIV
30mA TO 2A TRANSIENT
12VIN, 3.3VOUT
COUT = 47µF
IL
2A/DIV
500ns/DIV
36VIN TO 5VOUT AT 1A
8610ab G32
VOUT
200mV/DIV
8610ab G35
8610ab G31
VIN
100ms/DIV
2.5Ω LOAD
(2A IN REGULATION)
Start-Up Dropout Performance
VIN
2V/DIV
VOUT
VOUT
2V/DIV
8610ab G37
8610ab G34
VIN
VOUT
100ms/DIV
20Ω LOAD
(250mA IN REGULATION)
8610ab G38
8610abfa
For more information www.linear.com/LT8610A
9
LT8610A/LT8610AB Series
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 pulseskipping 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 during 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 connect 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 powered from this voltage. INTVCC maximum output current 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.
8610abfa
10
For more information www.linear.com/LT8610A
LT8610A/LT8610AB Series
BLOCK DIAGRAM
VIN
VIN
5, 6
CIN
R3
OPT
4
R4
OPT
15
EN/UV
PG
1V
+
–
SHDN
±9%
+
+
–
R1
R2
16
FB
SHDN
TSD
INTVCC UVLO
VIN UVLO
16
INTVCC
OSCILLATOR
200kHz TO 2.2MHz
VC
BST
BURST
DETECT
SWITCH
LOGIC
AND
ANTISHOOT
THROUGH
2.2µA
VOUT
14
13
CVCC
12
CBST
M1
L
SW
9-11
VOUT
COUT
M2
GND
SHDN
TSD
VIN UVLO
LT8610A/LT8610AB
ONLY
VOUT
BIAS
3.4V
REG
SLOPE COMP
ERROR
AMP
VOUT
C1
–
+
INTERNAL 0.97V REF
8
C1
R1
LT8610A-3.3/LT8610A-5
LT8610AB-3.3/LT8610AB-5
ONLY
R2
2
TR/SS
CSS
OPT
3
RT
1
SYNC
GND
17
8610ab BD
RT
8610abfa
For more information www.linear.com/LT8610A
11
LT8610A/LT8610AB Series
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 pulseskipping 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 applied 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.
8610abfa
12
For more information www.linear.com/LT8610A
LT8610A/LT8610AB Series
APPLICATIONS INFORMATION
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 minimizing 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 current pulses decreases (see Figure 1a) and the percentage
of time the LT8610A/LT8610AB is in sleep mode increases,
Burst Frequency
SWITCHING FREQUENCY (kHz)
800
700
600
LT8610A
500
LT8610AB
400
300
200
VIN = 12V
VOUT = 3.3V
L = 4.7µH
100
0
100 200 300 400 500 600 700 800
LOAD CURRENT (mA)
0
(1a)
LT8610A
IL
200mA/DIV
VOUT
10mV/DIV
VOUT = 3.3V
fSW = 700kHz
PULSE-SKIPPING MODE
70
LOAD CURRENT (mA)
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
8610ab F01a
Minimum Load to Full Frequency
80
resulting in much higher light load efficiency than for typical 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.
VSYNC = 0V
COUT = 47µF
L = 4.7µH
5µs/DIV
8610ab F02a
VSYNC = 0V
COUT = 47µF
L = 4.7µH
20µs/DIV
8610ab F02b
(2a)
60
50
LT8610AB
40
VSW
5V/DIV
30
IL
500mA/DIV
20
10
0
5
10
20
15
25
30
INPUT VOLTAGE (V)
(1b)
35
40
8610ab F01b
Figure 1. SW Frequency vs Load Information in
Burst Mode Operation (1a) and Pulse-Skipping Mode (1b)
VOUT
20mV/DIV
(2b)
Figure 2. Burst Mode Operation of LT8610A (2a) and
LT8610AB (2b)
For more information www.linear.com/LT8610A
8610abfa
13
LT8610A/LT8610AB Series
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 efficiency. 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 application, 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 ×2
20mV
47µF ×4
10mV
V
V 1
IQ = 1.7µA + OUT OUT
R1+R2 VIN n
(2)
where 1.7µA is the quiescent current of the LT8610A/
LT8610AB and the second term is the current in the feedback 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
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:
(1)
Reference designators refer to the Block Diagram. 1%
resistors are recommended to maintain output voltage
accuracy.
14
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:
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.
V
R1= R2 OUT – 1
0.970V
When using large FB resistors, a 4.7pF to 10pF phase-lead
capacitor should be connected from VOUT to FB.
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
– 5.2
fSW
For more information www.linear.com/LT8610A
(3)
8610abfa
LT8610A/LT8610AB Series
APPLICATIONS INFORMATION
where RT is in kΩ and fSW is the desired switching frequency 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
For applications that cannot allow deviation from the programmed switching frequency at low VIN/VOUT ratios use
the following formula to set switching frequency:
VIN(MIN) =
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 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) =
(
tON(MIN) VIN – VSW(TOP) + VSW(BOT)
VOUT + VSW(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 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.
Operating Frequency Selection and Trade-Offs
VOUT + VSW(BOT)
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.
)
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 overload 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:
(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 absolute 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.
L=
VOUT + VSW(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:
1
IL(PEAK) =ILOAD(MAX) + ∆IL
2
(7)
8610abfa
For more information www.linear.com/LT8610A
15
LT8610A/LT8610AB Series
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 –
∆IL
2
(8)
The peak-to-peak ripple current in the inductor can be
calculated as follows:
∆IL =
VOUT
L • fSW
V
• 1– OUT
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 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
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 efficiency. 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 application, 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 capacitor 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
8610abfa
16
For more information www.linear.com/LT8610A
LT8610A/LT8610AB Series
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 casual 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 (underdamped) 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). Typically, 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:
R3
VIN(EN) = +1 •1.0V
R4
(10)
where the LT8610A/LT8610AB 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).
8610abfa
For more information www.linear.com/LT8610A
17
LT8610A/LT8610AB Series
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) resistors should be large to minimize their effect on efficiency
at low loads.
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.
INTVCC Regulator
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.
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
The LT8610A/LT8610AB allows the user to program its output 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 softstart 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
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 amplitude should have valleys that are below 0.4V and peaks
above 2.4V (up to 6V).
The LT8610A/LT8610AB 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
LT8610A/LT8610AB may be synchronized over a 200kHz
8610abfa
18
For more information www.linear.com/LT8610A
LT8610A/LT8610AB Series
APPLICATIONS INFORMATION
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.
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.
D1
VIN
The LT8610A/LT8610AB does not operate in forced continuous mode regardless of SYNC signal. Never leave the
SYNC pin floating.
VIN
LT8610A/
LT8610AB
EN/UV
GND
8610ab F03
Figure 3. Reverse VIN Protection
Shorted and Reversed Input Protection
PCB Layout
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 switching of the top switch will be delayed until such time as the
inductor current falls to safe levels.
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
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 programmed 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.
8610abfa
For more information www.linear.com/LT8610A
19
LT8610A/LT8610AB Series
APPLICATIONS INFORMATION
can be left unconnected to help meet PCB clearance and
creepage requirements between the VIN and GND traces.
GND
High Temperature Considerations
16
TR/SS
2
15
RT
3
14 BIAS
4
13 INTVCC
5
12
6
11
7
10
8
9
EN/UV
VIN
FB
PG
BST
SW
GND
VOUT
VOUT LINE TO BIAS
VIAS TO GROUND PLANE
8610ab F04
OUTLINE OF LOCAL
GROUND PLANE
Figure 4. Recommended PCB Layout for the LT8610A/LT8610AB
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
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 subtracting 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.
140
CASE TEMPERATURE RISE (°C)
1
SYNC
VOUT
TA = 25°C
120
fSW = 2MHz
ILOAD = 3.5A
100
80
60
40
20
0
fSW = 2MHz
ILOAD = 2.5A
8
12
fSW = 1MHz
ILOAD = 3.5A
20
16
24
28
INPUT VOLTAGE (V)
32
36
8610ab F05
Figure 5. LT8610AB Case Temperature Rise
8610abfa
20
For more information www.linear.com/LT8610A
LT8610A/LT8610AB Series
TYPICAL APPLICATIONS
5V 2MHz Step-Down Converter
VIN
5.5V TO 42V
4.7µF
VIN
BST
0.1µF
2.2µH
EN/UV
LT8610A/
SW
LT8610AB
BIAS
SYNC
10nF
100k
1µF
TR/SS
INTVCC
RT
PG
1M
FB
VOUT
5V
3.5A
47µF*
1210
X7R
POWER GOOD
4.7pF
GND
18.2k
243k
fSW = 2MHz
8610ab TA02
L: XAL 5030
12V Step-Down Converter
VIN
12.5V TO 42V
4.7µF
VIN
BST
0.1µF
10µH
EN/UV
LT8610A/
SW
LT8610AB
BIAS
SYNC
10nF
100k
1µF
TR/SS
INTVCC
RT
PG
1M
FB
VOUT
12V
3.5A
47µF*
1210
X7R
POWER GOOD
10pF
GND
41.2k
88.7k
fSW = 1MHz
8610ab TA09
L: IHLP-2525CZ-01
5V Step-Down Converter
VIN
3.8V TO 42V
4.7µF
10nF
VIN
BST
EN/UV
LT8610A-5
0.1µF
10µH
SW
SYNC
BIAS
TR/SS
VOUT
100µF
1210
X5R
1µF
VOUT
12V
3.5A
100k
INTVCC
RT
PG
POWER GOOD
GND
110k
fSW = 400kHz
8610ab TA03
L: IHLP-2525CZ-01
*Consider doubling output capacitance for LT8610AB if application requires low output voltage ripple in Burst Mode operation.
8610abfa
For more information www.linear.com/LT8610A
21
LT8610A/LT8610AB Series
TYPICAL APPLICATIONS
1.8V 2MHz Step-Down Converter
VIN
3.4V TO 15V
(42V TRANSIENT)
VIN
4.7µF
BST
0.1µF
1µH
EN/UV
LT8610A/
PG
SW
LT8610AB
BIAS
SYNC
100µF*
1210
X5R
10nF
TR/SS
1µF
INTVCC
RT
VOUT
1.8V
3.5A
866k
FB
4.7pF
GND
18.2k
1M
fSW = 2MHz
8610ab TA06
L: IHLP-2020BZ-01
3.3V 2MHz Step-Down Converter
VIN
3.8V TO 27V
(42V TRANSIENT)
VIN
4.7µF
BST
0.1µF
2.2µH
EN/UV
LT8610A/
PG
SW
LT8610AB
BIAS
SYNC
47µF*
1210
X7R
10nF
TR/SS
1µF
INTVCC
RT
VOUT
3.3V
3.5A
1M
FB
4.7pF
GND
18.2k
412k
fSW = 2MHz
8610ab TA04
L: XAL 5030
1.8V Step-Down Converter
VIN
3.4V TO 42V
4.7µF
VIN
BST
EN/UV
LT8610A/
PG
SW
LT8610AB
BIAS
SYNC
0.1µF
4.7µH
47µF*
×3
1210
X7R
10nF
1µF
TR/SS
INTVCC
RT
110k
fSW = 400kHz
FB
VOUT
1.8V
3.5A
866k
4.7pF
GND
1M
8610ab TA07
L: IHLP-2020BZ-01
*Consider doubling output capacitance for LT8610AB if application requires low output voltage ripple in Burst Mode operation.
8610abfa
22
For more information www.linear.com/LT8610A
LT8610A/LT8610AB Series
TYPICAL APPLICATIONS
3.3V Step-Down Converter
VIN
3.8V TO 42V
4.7µF
10nF
1µF
VIN
BST
0.1µF
8.2µH
EN/UV
LT8610A-3.3
SW
PG
SYNC
BIAS
TR/SS
VOUT
INTVCC
RT
VOUT
3.3V
100µF 3.5A
1210
X5R
GND
110k
fSW = 400kHz
8610ab TA05
L: IHLP-2525BD-01
Ultralow EMI 5V 2.5A Step-Down Converter
VIN
5.5V TO 42V
FB1
BEAD
4.7µF
4.7µH
4.7µF
4.7µF
10nF
1µF
VIN
BST
EN/UV
LT8610A/
SW
PG
LT8610AB
SYNC
BIAS
TR/SS
FB
0.1µF
4.7µH
1M
47µF*
1210
X7R
VOUT
5V
3.5A
10pF
INTVCC
RT
GND
52.3k
fSW = 800kHz
243k
8610ab TA11
FB1: TDK MPZ2012S101A
L: IHLP-2020BZ-01
*Consider doubling output capacitance for LT8610AB if application requires low output voltage ripple in Burst Mode operation.
8610abfa
For more information www.linear.com/LT8610A
23
LT8610A/LT8610AB Series
PACKAGE DESCRIPTION
Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings.
MSE Package
16-Lead Plastic MSOP, Exposed Die Pad
(Reference LTC DWG # 05-08-1667 Rev F)
BOTTOM VIEW OF
EXPOSED PAD OPTION
2.845 ±0.102
(.112 ±.004)
5.10
(.201)
MIN
2.845 ±0.102
(.112 ±.004)
0.889 ±0.127
(.035 ±.005)
8
1
1.651 ±0.102
(.065 ±.004)
1.651 ±0.102 3.20 – 3.45
(.065 ±.004) (.126 – .136)
0.305 ±0.038
(.0120 ±.0015)
TYP
16
0.50
(.0197)
BSC
4.039 ±0.102
(.159 ±.004)
(NOTE 3)
RECOMMENDED SOLDER PAD LAYOUT
0.254
(.010)
0.35
REF
0.12 REF
DETAIL “B”
CORNER TAIL IS PART OF
DETAIL “B” THE LEADFRAME FEATURE.
FOR REFERENCE ONLY
9
NO MEASUREMENT PURPOSE
0.280 ±0.076
(.011 ±.003)
REF
16151413121110 9
DETAIL “A”
0° – 6° TYP
3.00 ±0.102
(.118 ±.004)
(NOTE 4)
4.90 ±0.152
(.193 ±.006)
GAUGE PLANE
0.53 ±0.152
(.021 ±.006)
DETAIL “A”
1.10
(.043)
MAX
0.18
(.007)
SEATING
PLANE
0.17 – 0.27
(.007 – .011)
TYP
1234567 8
0.50
(.0197)
BSC
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.
0.86
(.034)
REF
0.1016 ±0.0508
(.004 ±.002)
MSOP (MSE16) 0213 REV F
8610abfa
24
For more information www.linear.com/LT8610A
LT8610A/LT8610AB Series
REVISION HISTORY
REV
DATE
DESCRIPTION
PAGE NUMBER
A
08/14
Added fixed output options.
1 - 4, 10, 12, 13
Clarified Applications Information.
14, 18
8610abfa
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 representation that the interconnection
of its circuits
as described
herein will not infringe on existing patent rights.
For more
information
www.linear.com/LT8610A
25
LT8610A/LT8610AB Series
TYPICAL APPLICATION
3.3V and 1.8V with Ratio Tracking
VIN
3.8V TO 42V
4.7µF
VIN
BST
EN/UV
LT8610A/
PG
LT8610AB
SYNC
VIN
3.8V TO 27V
0.1µF
5.6µH
SW
47µF*
1210
X7R
10nF
1µF
BIAS
TR/SS
INTVCC
RT
FB
Ultralow IQ 2.5V, 3.3V Step-Down with LDO
VIN
4.7µF
VOUT1
3.3V
3.5A
PG
232k
BIAS
TR/SS
INTVCC
RT
GND
VOUT
GND
18.2k
fSW = 500kHz
fSW = 2MHz
L: IHLP-2020BZ-01
4.7µF
24.3k
VIN
BST
EN/UV
LT8610A/
PG
LT8610AB
SYNC
SW
BIAS
TR/SS
10k
1µF
INTVCC
RT
FB
0.1µF
3.3µH
VOUT1
3.3V
3.5A
47µF
×2
1210
X7R
LT8610AB-3.3
1µF
97.6k
0.1µF
2.2µH
SW
SYNC
10nF
4.7pF
88.7k
BST
EN/UV
IN
OUT
LT3008-2.5
VOUT2
2.5V
2.2µF 20mA
SHDN SENSE
8610ab TA10
VOUT2
1.8V
100µF* 3.5A
1210
X5R
80.6k
4.7pF
GND
88.7k
fSW = 500kHz
93.1k
8610ab TA08
L: IHLP-2020CZ-01, 5.6µH
L: IHLP-2020CZ-01, 3.3µH
*Consider doubling output capacitance for LT8610AB if application requires low output voltage ripple in Burst Mode operation.
RELATED PARTS
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 Transient 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
8610abfa
26 Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
For more information www.linear.com/LT8610A
(408) 432-1900 ● FAX: (408) 434-0507
●
www.linear.com/LT8610A
LT 0814 REV A • PRINTED IN USA
LINEAR TECHNOLOGY CORPORATION 2013
工商网监
湘ICP备2023018690号
