LT8636 [ADI]
42V, 5A/7A Peak Synchronous Step-Down Silent Switcher with 2.5μA Quiescent Current;
| 型号： | LT8636 |
| 厂家： | 
ADI |
| 描述： | 42V, 5A/7A Peak Synchronous Step-Down Silent Switcher with 2.5μA Quiescent Current |
| 文件： | 总32页 (文件大小：2612K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
LT8636/LT8637
42V, 5A/7A Peak Synchronous Step-Down
Silent Switcher with 2.5µA Quiescent Current
FEATURES
n
DESCRIPTION
Silent Switcher® Architecture
The LT®8636/LT8637 synchronous step-down regulator
features Silent Switcher architecture designed to minimize
EMI emissions while delivering high efficiency at high
switching frequencies. Peak current mode control with
a 30ns minimum on-time allows high step-down ratios
even at high switching frequencies.
n
Ultralow EMI Emissions
n
Optional Spread Spectrum Modulation
n
High Efficiency at High Frequency
n
Up to 96% Efficiency at 1MHz, 12V to 5V
Up to 95% Efficiency at 2MHz, 12V to 5V
IN
IN
OUT
OUT
n
n
n
n
Wide Input Voltage Range: 3.4V to 42V
The LT8636’s ultralow 2.5µA quiescent current—with the
output in full regulation—enables applications requiring
highest efficiency at very small load currents. The LT8637
has external compensation to enable current sharing and
fast transient response at high switching frequencies. A
CLKOUT pin enables synchronizing other regulators to
the LT8636/LT8637.
5A Maximum Continuous, 7A Peak Transient Output
Ultralow Quiescent Current Burst Mode® Operation
n
2.5µA I Regulating 12V to 3.3V
(LT8636)
Q
IN
P-P
OUT
n
Output Ripple < 10mV
n
External Compensation: Fast Transient Response
and Current Sharing (LT8637)
n
n
n
n
n
n
n
Fast Minimum Switch On-Time: 30ns
Low Dropout Under All Conditions: 100mV at 1A
Forced Continuous Mode
Adjustable and Synchronizable: 200kHz to 3MHz
Output Soft-Start and Power Good
Small 20-Lead 4mm × 3mm LQFN Package
AEC-Q100 Qualified for Automotive Applications
Burst Mode operation enables ultralow standby current
consumption, forced continuous mode can control fre-
quency harmonics across the entire output load range, or
spread spectrum operation can further reduce EMI emis-
sions. Soft-start and tracking functionality is accessed
via the TR/SS pin, and an accurate input voltage UVLO
threshold can be set using the EN/UV pin.
All registered trademarks and trademarks are the property of their respective owners. Protected
by U.S. patents, including 8823345.
APPLICATIONS
n
Automotive and Industrial Supplies
General Purpose Step-Down
n
TYPICAL APPLICATION
5V, 5A Step-Down Converter
12VIN to 5VOUT Efficiency
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Rev. C
1
Document Feedback
For more information www.analog.com
LT8636/LT8637
ABSOLUTE MAXIMUM RATINGS
(Note 1)
Operating Junction Temperature Range (Note 2)
V , EN/UV, PG..........................................................42V
IN
LT8636E/LT8637E ............................. –40°C to 125°C
LT8636J/LT8637J.............................. –40°C to 150°C
LT8636H............................................ –40°C to 150°C
LT8636MP......................................... –55°C to 150°C
Storage Temperature Range .................. –65°C to 150°C
Maximum Reflow (Package Body) Temperature.....260°C
BIAS..........................................................................25V
FB, TR/SS . .................................................................4V
SYNC/MODE Voltage . ................................................6V
PIN CONFIGURATION
LT8636
LT8637
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ORDER INFORMATION
PACKAGE
TYPE**
MSL
PART NUMBER
LT8636EV#PBF
LT8636JV#PBF
LT8636HV#PBF
LT8636MPV#PBF
LT8637EV#PBF
PART MARKING*
FINISH CODE
PAD FINISH
RATING
TEMPERATURE RANGE
–40°C to 125°C
–40°C to 150°C
–40°C to 150°C
–55°C to 150°C
–40°C to 125°C
–40°C to 150°C
8636
LQFN (Laminate Package
with QFN Footprint)
e4
Au (RoHS)
3
8637
LT8637JV#PBF
Rev. C
2
For more information www.analog.com
LT8636/LT8637
ORDER INFORMATION
PACKAGE
TYPE**
MSL
RATING
PART NUMBER
PART MARKING*
FINISH CODE
PAD FINISH
TEMPERATURE RANGE
AUTOMOTIVE PRODUCTS***
LT8636EV#WPBF
–40°C to 125°C
–40°C to 150°C
–40°C to 150°C
–40°C to 150°C
–40°C to 125°C
–40°C to 150°C
LT8636JV#WPBF
8636
8637
LT8636JV#WTRPBF
LT8636HV#WPBF
LQFN (Laminate Package
with QFN Footprint)
e4
Au (RoHS)
3
LT8637EV#WPBF
LT8637JV#WPBF
• Contact the factory for parts specified with wider operating temperature
ranges. *Device temperature grade is identified by a label on the
shipping container.
• Recommended PCB Assembly and Manufacturing Procedures
• Package and Tray Drawings
• Pad finish code is per IPC/JEDEC J-STD-609.
Parts ending with PBF are RoHS and WEEE compliant. **The LT8636/LT8637 package has the same dimensions as a standard 4mm × 3mm QFN package.
***Versions of this part are available with controlled manufacturing to support the quality and reliability requirements of automotive applications. These
models are designated with a #W suffix. Only the automotive grade products shown are available for use in automotive applications. Contact your
local Analog Devices account representative for specific product ordering information and to obtain the specific Automotive Reliability reports for
these models.
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
l
l
l
l
Minimum Input Voltage
3.0
3.4
V
V
Quiescent Current in Shutdown
V
EN/UV
V
EN/UV
V
EN/UV
= 0V
1
1
3
10
µA
µA
IN
LT8636 V Quiescent Current in Sleep
= 2V, V > 0.97V, V
= 0V
1.7
1.7
4
10
µA
µA
IN
FB
SYNC
(Internal Compensation)
LT8637 V Quiescent Current in Sleep
= 2V, V > 0.97V, V
= 0V, V
= 0V
230
230
290
340
µA
µA
IN
FB
SYNC
BIAS
(External Compensation)
V
V
V
= 2V, V > 0.97V, V
= 0V, V
= 0V, V
= 5V
= 5V
19
25
µA
µA
µA
EN/UV
FB
SYNC
SYNC
BIAS
BIAS
LT8637 BIAS Quiescent Current in Sleep
= 2V, V > 0.97V, V
200
220
260
390
EN/UV
FB
LT8636 V Current in Regulation
= 0.97V, V = 6V, I
= 1mA, V
= 0
IN
OUT
IN
LOAD
SYNC
Feedback Reference Voltage
V
V
= 6V
0.966
0.956
0.970
0.970
0.974
0.982
V
V
IN
IN
l
l
= 6V
Feedback Voltage Line Regulation
Feedback Pin Input Current
V
V
= 4.0V to 36V
= 1V
0.004
0.02
20
%/V
nA
IN
–20
FB
LT8637 Error Amp Transconductance
LT8637 Error Amp Gain
V = 1.25V
1.7
260
350
350
5
mS
C
LT8637 V Source Current
V
V
= 0.77V, V = 1.25V
µA
µA
A/V
V
C
FB
C
LT8637 V Sink Current
= 1.17V, V = 1.25V
C
C
FB
LT8637 V Pin to Switch Current Gain
C
LT8637 V Clamp Voltage
2.6
14
C
BIAS Pin Current Consumption
V
BIAS
= 3.3V, f = 2MHz
mA
SW
Rev. C
3
For more information www.analog.com
LT8636/LT8637
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
l
l
Minimum On-Time
I
I
= 1.5A, SYNC = 0V
= 1.5A, SYNC = 2V
30
30
50
45
ns
ns
LOAD
LOAD
Minimum Off-Time
Oscillator Frequency
80
110
ns
l
l
l
R = 221k
180
665
1.8
210
700
1.95
240
735
2.1
kHz
kHz
MHz
T
R = 60.4k
T
R = 18.2k
T
Top Power NMOS On-Resistance
Top Power NMOS Current Limit
Bottom Power NMOS On-Resistance
SW Leakage Current
I
= 1A
66
10
27
mΩ
A
SW
l
l
7.5
12.5
V
V
= 3.4V, I = 1A
mΩ
µA
V
INTVCC
SW
= 42V, V = 0V, 42V
–3
3
IN
SW
EN/UV Pin Threshold
EN/UV Rising
0.94
1.0
40
1.06
EN/UV Pin Hysteresis
mV
nA
%
EN/UV Pin Current
V
V
V
= 2V
–20
5
20
EN/UV
l
l
PG Upper Threshold Offset from V
Falling
7.5
–8
10.25
–5.25
FB
FB
FB
PG Lower Threshold Offset from V
PG Hysteresis
Rising
–10.75
%
FB
0.2
%
PG Leakage
V
V
= 3.3V
= 0.1V
–80
80
nA
Ω
PG
l
PG Pull-Down Resistance
SYNC/MODE Threshold
700
2000
PG
l
l
l
SYNC/MODE DC and Clock Low Level Voltage
SYNC/MODE Clock High Level Voltage
SYNC/MODE DC High Level Voltage
0.7
2.2
0.9
1.2
2.55
V
V
V
1.4
2.9
Spread Spectrum Modulation
Frequency Range
R = 60.4k, V
= 3.3V
22
%
T
SYNC
Spread Spectrum Modulation Frequency
TR/SS Source Current
V
= 3.3V
3
kHz
µA
Ω
SYNC
l
1.2
35
1.9
200
37
2.6
39
TR/SS Pull-Down Resistance
Fault Condition, TR/SS = 0.1V
Rising
V
IN
to Disable Forced Continuous Mode
V
V
IN
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.
lifetime is derated at junction temperatures greater than 125°C. The junction
temperature (T , in °C) is calculated from the ambient temperature (T in
J
A
°C) and power dissipation (PD, in Watts) according to the formula:
T = T + (PD • θ )
JA
J
A
Note 2: The LT8636E 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
LT8636J and LT8636H are guaranteed over the full –40°C to 150°C
operating junction temperature range. High junction temperatures degrade
operating lifetimes. The LT8636MP is 100% tested and guaranteed over
the full –55°C to 150°C operating junction temperature range. Operating
where θ (in °C/W) is the package thermal impedance.
JA
Note 3: θ values determined per JEDEC 51-7, 51-12. See the Applications
Information section for information on improving the thermal resistance
and for actual temperature measurements of a demo board in typical
operating conditions.
Note 4: 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.
Rev. C
4
For more information www.analog.com
LT8636/LT8637
TYPICAL PERFORMANCE CHARACTERISTICS
12VIN to 5VOUT Efficiency
vs Frequency
12VIN to 3.3VOUT Efficiency
vs Frequency
Efficiency at 5VOUT
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ꢀꢁꢂꢃ CꢄRRꢅꢆꢇ ꢈꢂꢉ
ꢀꢁꢂꢃ CꢄRRꢅꢆꢇ ꢈꢂꢉ
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LT8636 Low Load Efficiency at
5VOUT
LT8637 Low Load Efficiency at
5VOUT
Efficiency at 3.3VOUT
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ꢀ.ꢁ
ꢀ
ꢀꢁꢁ
ꢀꢁꢁ
ꢀꢁ
ꢀꢁ
ꢀꢁ
ꢀꢁ
ꢀꢁ
ꢀꢁ
ꢀꢁ
ꢀꢁ
ꢀꢁ
ꢀ ꢁ ꢂꢃꢀꢄꢅꢄꢅꢆ ꢇ.ꢇꢈꢉ
ꢀꢁ
ꢀꢁ
ꢀꢁ
ꢀꢁ
ꢀꢁ
ꢀꢁ
ꢀꢁ
ꢀꢁ
ꢀꢁꢁꢂCꢂꢀꢃCꢄ
ꢀꢁꢂꢃꢄ ꢅꢆꢇe ꢈꢉꢊRꢋꢌꢍꢈꢎ
ꢀ ꢁꢂꢃꢄ
ꢀꢁꢂꢃR ꢄꢁꢅꢅ
ꢀ
ꢀꢁ
ꢀ
ꢀ
ꢀ
ꢀ ꢁꢂꢃ
ꢀ ꢁꢂꢃ
ꢀ ꢁꢂꢃ
ꢀꢁ
ꢀꢁ
ꢀꢁ
ꢀ ꢁ ꢂꢃꢀꢄꢅꢄꢅꢆ ꢇ.ꢈꢉꢊ
ꢀ
ꢀ ꢁꢂꢃꢄ
ꢀꢁ
ꢀ
ꢀ
ꢀ
ꢀ ꢁꢂꢃ
ꢀ
ꢀ
ꢀ
ꢀ ꢁꢂꢃ
ꢀꢁ
ꢀꢁ
ꢀꢁ
ꢀꢁ
ꢀꢁ
ꢀ ꢁꢂꢃ
ꢀ ꢁꢂꢃ
ꢀ
ꢀ ꢁꢂꢃꢄ
ꢀꢁ
ꢀ ꢁꢂꢃ
ꢀ ꢁꢂꢃ
ꢀꢁ
ꢀ ꢁ ꢂꢃꢀꢄꢅꢆꢅꢆꢇꢈꢉꢊꢋꢌ ꢍ.ꢎꢏꢃ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ.ꢀꢁ
ꢀ.ꢁ
ꢀ
ꢀꢁ
ꢀꢁꢁ
ꢀꢁꢁꢁ
ꢀ.ꢁ
ꢀ
ꢀꢁ
ꢀꢁꢁ
ꢀꢁꢁꢁ
ꢀꢁꢂꢃ CꢄRRꢅꢆꢇ ꢈꢂꢉ
ꢀꢁꢂꢃ CꢄRRꢅꢆꢇ ꢈꢉꢂꢊ
ꢀꢁꢂꢃ CꢄRRꢅꢆꢇ ꢈꢉꢂꢊ
ꢀꢁꢂꢁ ꢃꢄꢅ
ꢀꢁꢂꢁ ꢃꢄꢅ
ꢀꢁꢂꢁ ꢃꢄꢁ
LT8636 Low Load Efficiency at
3.3VOUT
LT8637 Low Load Efficiency at
3.3VOUT
Efficiency vs Frequency
ꢀꢁꢁ
ꢀꢁ
ꢀꢁ
ꢀꢁ
ꢀꢁ
ꢀꢁ
ꢀꢁ
ꢀꢁ
ꢀꢁ
ꢀꢁꢁ
ꢀꢁ
ꢀꢁ
ꢀꢁ
ꢀꢁ
ꢀꢁ
ꢀꢁ
ꢀꢁ
ꢀꢁ
ꢀꢁ
ꢀꢁ
ꢀꢁ
ꢀꢁ
ꢀꢁ
ꢀꢀ
ꢀꢁ
ꢀꢁ
ꢀꢁ
ꢀꢁ
ꢀꢁꢂꢃꢄ ꢅꢆꢇe ꢈꢉꢊRꢋꢌꢍꢈꢎ
ꢀ ꢁꢂꢃꢄ
ꢀ
ꢀ
ꢀꢁ
ꢀ
ꢀꢁ
ꢀ
ꢀꢁ
ꢀ ꢁꢂꢃ
ꢀ ꢁꢂꢃ
ꢀ ꢁꢂꢃ
ꢀꢁ
ꢀ ꢁ ꢂꢃꢀꢄꢅꢄꢅꢆ ꢇ.ꢈꢉꢊ
ꢀ
ꢃ ꢄꢅꢀ
ꢁꢂ
ꢀ
ꢀ
ꢀ
ꢀ ꢁꢂꢃ
ꢀ ꢁꢂꢃ
ꢀ ꢁꢂꢃ
ꢀꢁ
ꢀꢁ
ꢀꢁ
ꢀ
ꢀ ꢁ.ꢁꢂ
ꢀꢁꢂ
ꢀ
ꢀ ꢁꢂꢃꢄ
ꢀꢁ
ꢀ
ꢀ ꢁꢂ
ꢀꢁꢂꢃ
ꢀ ꢁ ꢂꢃꢀꢄꢅꢆꢅꢆꢇꢈꢉꢊꢋꢌ ꢍ.ꢎꢏꢃ
ꢀ ꢁ ꢂꢃꢀꢄꢅꢆꢅꢆꢇꢈꢉꢊꢋꢌ ꢍ.ꢎꢏꢃ
ꢀ.ꢀꢁ
ꢀ.ꢁ
ꢀ
ꢀꢁ
ꢀꢁꢁ
ꢀꢁꢁꢁ
ꢀ.ꢁ
ꢀ
ꢀꢁ
ꢀꢁꢁ
ꢀꢁꢁꢁ
ꢀ
ꢀ.ꢁ
ꢀ
ꢀ.ꢁ
ꢀ
ꢀ.ꢁ
ꢀ
ꢀꢁꢂꢃ CꢄRRꢅꢆꢇ ꢈꢉꢂꢊ
ꢀꢁꢂꢃ CꢄRRꢅꢆꢇ ꢈꢉꢂꢊ
ꢀꢁꢂꢃCꢄꢂꢅꢆ ꢇRꢈꢉꢊꢈꢅCꢋ ꢌꢍꢄꢎꢏ
ꢀꢁꢂꢁ ꢃꢄꢅ
ꢀꢁꢂꢁ ꢃꢄꢀ
ꢀꢁꢂꢁ ꢃꢄꢅ
Rev. C
5
For more information www.analog.com
LT8636/LT8637
TYPICAL PERFORMANCE CHARACTERISTICS
Burst Mode Operation Efficiency
vs Inductor Value (LT8636)
Reference Voltage
EN Pin Thresholds
ꢀ.ꢁꢂ
ꢀ.ꢁꢂ
ꢀ.ꢁꢀ
ꢀ.ꢁꢁ
ꢀ.ꢁꢁ
ꢀ.ꢁꢂ
ꢀ.ꢁꢂ
ꢀ.ꢁꢂ
ꢀ.ꢁꢂ
ꢀꢁꢁ
ꢀꢁ
ꢀꢁ
ꢀꢁ
ꢀꢁ
ꢀꢁ
ꢀꢁ
ꢀꢁ
ꢀꢁꢀ
ꢀꢁꢁ
ꢀꢁꢂ
ꢀꢁꢂ
ꢀꢁꢂ
ꢀꢁꢀ
ꢀꢁꢂ
ꢀꢁꢂ
ꢀꢁꢂ
ꢀꢁꢂ
ꢀ
ꢀ ꢁꢂꢃ
ꢀꢁ
ꢀꢁ Rꢂꢃꢂꢁꢄ
ꢀ
ꢀ ꢁꢂꢃ
ꢀꢁ
ꢀꢁ ꢂꢃꢄꢄꢅꢁꢆ
ꢀ
ꢀꢁꢂꢃ
ꢀ ꢁ ꢂꢃꢀꢄꢅꢆꢅꢆꢇꢈꢉꢊꢋ
ꢀ ꢁꢂ
ꢀꢁꢂ
ꢀ
ꢀ ꢁꢂꢃꢄ
ꢀꢁꢂ ꢀꢁꢂ
ꢀ
ꢀꢁ ꢀꢁ ꢀꢁ ꢀꢁꢁ ꢀꢁꢂ ꢀꢁꢂ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀꢁꢂ ꢀꢁꢂ
ꢀ
ꢀꢁ ꢀꢁ ꢀꢁ ꢀꢁꢁ ꢀꢁꢂ ꢀꢁꢂ
ꢀꢁꢂꢃꢁRꢄꢀꢅRꢁ ꢆꢇCꢈ
ꢀꢁꢂꢃCꢄꢅR ꢆꢇꢈꢃꢉ ꢊꢋꢌꢍ
ꢀꢁꢂꢃꢁRꢄꢀꢅRꢁ ꢆꢇCꢈ
ꢀꢁꢂꢁ ꢃꢄꢅ
ꢀꢁꢂꢁ ꢃꢄꢅ
ꢀꢁꢂꢁ ꢃꢄꢄ
LT8636 Load Regulation
LT8636 Line Regulation
LT8637 Load Regulation
ꢀ.ꢁꢂ
ꢀ.ꢁꢀ
ꢀ.ꢀꢁ
ꢀ
ꢀ.ꢁꢂ
ꢀ.ꢁꢀ
ꢀ.ꢁꢀ
ꢀ.ꢁꢀ
ꢀ.ꢀꢁ
ꢀ.ꢁꢀ
ꢀ.ꢀꢁ
ꢀ.ꢁꢀ
ꢀ.ꢀꢁ
ꢀ.ꢀꢁ
ꢀ.ꢀꢀ
ꢀ.ꢀꢀ
ꢀꢁ.ꢂꢁ
ꢀꢁ.ꢂꢁ
ꢀꢁ.ꢂꢁ
ꢀꢁ.ꢂꢁ
ꢀ.ꢀꢁ
ꢀꢁ.ꢂꢁ
ꢀꢁ.ꢂꢃ
ꢀꢁ.ꢁꢂ
ꢀꢁ.ꢁꢂ
ꢀꢁ.ꢁꢂ
ꢀꢁ.ꢁꢂ
ꢀ
ꢀ
ꢀ
ꢀ ꢁꢂ
ꢀꢁꢂ
ꢀꢁ
ꢀ
ꢀ
ꢀ
ꢀ ꢁꢂ
ꢀꢁꢂ
ꢀ ꢁꢂꢃ
ꢀ
ꢀꢁꢂꢃ
ꢀ ꢁꢂ
ꢀ ꢁꢂꢃ
ꢀꢁꢂ
ꢀꢁ
ꢀꢁꢂC
ꢀ ꢁꢂ
ꢀ
ꢀ ꢁꢂ
ꢀꢁꢂC
ꢀ ꢁꢂ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀꢁ ꢀꢁ ꢀꢁ ꢀꢁ ꢀꢁ ꢀꢁ ꢀꢁ ꢀꢁ
ꢀꢁꢂꢃꢄ ꢅꢆꢇꢄꢈꢉꢊ ꢋꢅꢌ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀꢁꢂꢃ CꢄRRꢅꢆꢇ ꢈꢂꢉ
ꢀꢁꢂꢃ CꢄRRꢅꢆꢇ ꢈꢂꢉ
ꢀꢁꢂꢁ ꢃꢄꢂ
ꢀꢁꢂꢁ ꢃꢄꢅ
ꢀꢁꢂꢁ ꢃꢄꢅ
LT8637 Line Regulation
LT8636 No-Load Supply Current
LT8637 No-Load Supply Current
ꢀ.ꢁ
ꢀ.ꢁ
ꢀ.ꢁ
ꢀ.ꢁ
ꢀ.ꢁ
ꢀ.ꢁ
ꢀ.ꢁ
ꢀꢀꢁ
ꢀꢁꢁ
ꢀꢁꢂ
ꢀꢁꢂ
ꢀꢁꢂ
ꢀꢁꢁ
ꢀꢁ
ꢀ.ꢁꢂ
ꢀ.ꢁꢂ
ꢀ.ꢀꢁ
ꢀ.ꢀꢁ
ꢀ.ꢀꢁ
ꢀ
ꢀ
ꢀ ꢁꢂ
ꢀꢁꢂ
ꢀ ꢁ ꢂ.ꢃꢄꢅ
ꢀꢁ Rꢂꢃꢄꢅꢆꢇꢀꢈꢁ
ꢀꢁ.ꢁꢂ
ꢀꢁ.ꢁꢂ
ꢀꢁ.ꢁꢂ
ꢀꢁ.ꢂꢃ
ꢀꢁ.ꢂꢃ
ꢀ
ꢀ ꢁ.ꢁꢂ
ꢀꢁꢂ
ꢀ ꢁ ꢂ.ꢃꢄꢅ
ꢆꢇꢈꢉ ꢁ ꢊ
ꢀꢁ
ꢀ
ꢀꢁꢂꢃ
ꢀ ꢁꢂ
ꢀ ꢁꢂ
ꢀꢁꢂ
ꢋꢌꢍ
ꢀ
ꢇꢎ Rꢏꢐꢌꢀꢈꢍꢇꢋꢎ
ꢀꢁ
ꢀ
ꢀ
ꢀꢁ ꢀꢁ ꢀꢁ ꢀꢁ ꢀꢁ ꢀꢁ ꢀꢁ ꢀꢁ
ꢀ
ꢀꢁ ꢀꢁ ꢀꢁ ꢀꢁ ꢀꢁ ꢀꢁ ꢀꢁ ꢀꢁ
ꢀ
ꢀꢁ ꢀꢁ ꢀꢁ ꢀꢁ ꢀꢁ ꢀꢁ ꢀꢁ ꢀꢁ
ꢀꢁꢂꢃꢄ ꢅꢆꢇꢄꢈꢉꢊ ꢋꢅꢌ
ꢀꢁꢂꢃꢄ ꢅꢆꢇꢄꢈꢉꢊ ꢋꢅꢌ
ꢀꢁꢂꢃꢄ ꢅꢆꢇꢄꢈꢉꢊ ꢋꢅꢌ
ꢀꢁꢂꢁ ꢃꢄꢅ
ꢀꢁꢂꢁ ꢃꢄꢀ
ꢀꢁꢂꢁ ꢃꢄꢁ
Rev. C
6
For more information www.analog.com
LT8636/LT8637
TYPICAL PERFORMANCE CHARACTERISTICS
Top FET Current Limit vs Duty Cycle
Top FET Current Limit
Switch Drop vs Temperature
ꢀꢀ.ꢁ
ꢀꢁ.ꢂ
ꢀꢁ.ꢁ
ꢀ.ꢁ
ꢀꢁꢂ
ꢀꢁꢂ
ꢀꢁꢁ
ꢀꢁ
ꢀꢁ
ꢀꢀ
ꢀꢁ
ꢀ
ꢀꢁꢂꢃCꢄ CꢅRRꢆꢇꢃ ꢈ ꢉꢊ
ꢀ.ꢁ
ꢀꢁꢂ ꢃꢄꢅꢀCꢆ
ꢀ.ꢁ
ꢀꢁ ꢂC
ꢀ.ꢁ
ꢀꢁ
ꢀ.ꢁ
ꢀ.ꢁ
ꢀꢁ
ꢀꢁꢂꢂꢁꢃ ꢄꢅꢆꢂCꢇ
ꢀ.ꢁ
ꢀ.ꢁ
ꢀ
ꢀ
ꢀ.ꢁ
ꢀ.ꢁ
ꢀ.ꢁ
ꢀ.ꢁ
ꢀ.ꢁ
ꢀꢁꢂ ꢀꢁꢂ
ꢀ
ꢀꢁ
ꢀꢁ
ꢀꢁ ꢀꢁꢁ ꢀꢁꢂ
ꢀꢁꢂ ꢀꢁꢂ
ꢀ
ꢀꢁ ꢀꢁ ꢀꢁ ꢀꢁꢁ ꢀꢁꢂ ꢀꢁꢂ
ꢀꢁꢂꢃ CꢃCꢄꢅ
ꢀꢁꢂꢃꢁRꢄꢀꢅRꢁ ꢆꢇCꢈ
ꢀꢁꢂꢃꢁRꢄꢀꢅRꢁ ꢆꢇCꢈ
ꢀꢁꢂꢁ ꢃꢄꢅ
ꢀꢁꢂꢁ ꢃꢄꢅ
ꢀꢁꢂꢁ ꢃꢄꢅ
Dropout Voltage
Switch Drop vs Switch Current
Minimum On-Time
ꢀꢀ
ꢀꢁ
ꢀꢁ
ꢀꢁ
ꢀꢁ
ꢀꢁ
ꢀꢁ
ꢀꢁꢁ
ꢀꢁꢂ
ꢀꢁꢁ
ꢀꢁꢂ
ꢀꢁꢁ
ꢀꢁꢂ
ꢀꢁꢁ
ꢀꢁꢂ
ꢀꢁꢁ
ꢀꢁ
ꢀꢁꢁ
ꢀ
ꢀ ꢁꢂ
ꢀꢁꢂ
ꢀꢁ
ꢀꢁꢂꢃꢄ ꢅꢆꢇe ꢈꢉꢊRꢋꢌꢍꢈꢎ
ꢀꢁRCꢂꢃ Cꢁꢄꢅꢆꢄꢇꢁꢇꢈ ꢉꢁꢃꢂ
ꢀ
ꢀꢁꢂ ꢂꢃ Rꢁꢄꢅꢆꢇꢂꢁ ꢇꢂ ꢈꢉ
ꢀꢁꢁ ꢀ ꢁ ꢂꢃꢀꢄꢅꢆꢅꢆꢇꢈꢉꢊꢋꢌ ꢋꢍꢃ
ꢀꢁꢁ
ꢀꢁꢁ
ꢀꢁꢁ
ꢀꢁꢁ
ꢀ
ꢀꢁꢂ ꢃꢄꢅꢀCꢆ
ꢀ
ꢀ ꢁꢂ
ꢀꢁꢂꢃ
ꢀꢁꢂ
ꢀ
ꢀ ꢁ.ꢂꢃꢄ
ꢀ
ꢃ ꢄꢅꢆꢇ
ꢀꢁꢂꢂꢁꢃ ꢄꢅꢆꢂCꢇ
ꢁꢂ
ꢀ
ꢀꢁꢂ ꢀꢁꢂ
ꢀ
ꢀꢁ
ꢀꢁ
ꢀꢁ ꢀꢁꢁ ꢀꢁꢂ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ.ꢁ
ꢀ
ꢀ.ꢁ
ꢀ
ꢀ.ꢁ
ꢀ
ꢀ.ꢁ
ꢀ
ꢀ.ꢁ
ꢀ
ꢀꢁꢂꢃꢁRꢄꢀꢅRꢁ ꢆꢇCꢈ
ꢀꢁꢂꢃCꢄ CꢅRRꢆꢇꢃ ꢈꢉꢊ
ꢀꢁꢂꢃ CꢄRRꢅꢆꢇ ꢈꢂꢉ
ꢀꢁꢂꢁ ꢃꢄꢅ
ꢀꢁꢂꢁ ꢃꢄꢄ
ꢀꢁꢂꢁ ꢃꢄꢂ
Switching Frequency
Burst Frequency
LT8636 Soft-Start Tracking
ꢀꢁꢂꢂ
ꢀꢁꢁꢁ
ꢀꢁꢁ
ꢀꢁꢁ
ꢀꢁꢁ
ꢀꢁꢁ
ꢀ
.
.
ꢀꢁꢂ
ꢀꢁꢂ
ꢀꢁꢂ
ꢀꢁꢂ
ꢀꢁꢁ
ꢀꢁꢂ
ꢀꢁꢂ
ꢀꢁꢂ
ꢀꢀꢁ
R
ꢀ
ꢀ ꢁꢂ.ꢃꢄ
.
.
.
.
ꢀRꢁꢂꢃ ꢄꢅꢆꢇ ꢅꢄꢄꢈꢉCꢅꢃꢉꢁꢂ
ꢀ
ꢀꢁꢂ
ꢀ ꢁꢂꢃ
ꢀ ꢁꢂ
ꢀꢁ
ꢀ
.
.
.
ꢀ
ꢀꢁꢁ
ꢀꢁꢁ
ꢀꢁꢁ
ꢀꢁꢁ
ꢀꢁꢁ
ꢀꢁꢁ
.
.
.
.
ꢀꢁꢂ ꢀꢁꢂ
ꢀ
ꢀꢁ ꢀꢁ ꢀꢁ ꢀꢁꢁ ꢀꢁꢂ ꢀꢁꢂ
ꢀꢁꢂꢃ CꢄRRꢅꢆꢇ ꢈꢉꢂꢊ
ꢀꢁꢂꢃꢁRꢄꢀꢅRꢁ ꢆꢇCꢈ
R
ꢀꢁꢂꢁ ꢃꢄꢁ
ꢀꢁꢂꢁ ꢃꢄꢅ
Rev. C
7
For more information www.analog.com
LT8636/LT8637
TYPICAL PERFORMANCE CHARACTERISTICS
LT8637 Soft-Start Tracking
LT8637 Error Amp Output Current
Soft-Start Current
ꢀ.ꢁ
ꢀ.ꢁ
ꢀ.ꢁ
ꢀ.ꢁ
ꢀ.ꢁ
ꢀ.ꢁ
ꢀ
ꢀꢁꢁ
ꢀꢁꢂ
ꢀ.ꢀ
ꢀ.ꢁ
ꢀ.ꢁ
ꢀ.ꢁ
ꢀ.ꢁ
ꢀ.ꢁ
ꢀ.ꢁ
ꢀ.ꢁ
ꢀ.ꢁ
ꢀ
ꢀ ꢁ.ꢂꢃ
ꢀꢀ
ꢀꢁꢂ
ꢀꢁꢂ
ꢀ
ꢀꢁꢂꢃ
ꢀꢁꢂꢃ
ꢀꢁꢂꢃ
ꢀꢁꢂꢂ
ꢀ
ꢀ ꢁ.ꢂꢃꢄ
C
ꢀ
ꢀ.ꢁ ꢀ.ꢁ ꢀ.ꢁ ꢀ.ꢁ
ꢀ
ꢀ.ꢁ ꢀ.ꢁ ꢀ.ꢁ
ꢀꢁꢂꢂ
ꢀꢁꢂꢂ
ꢀ
ꢀꢁꢁ
ꢀꢁꢁ
ꢀꢁꢂ ꢀꢁꢂ
ꢀ
ꢀꢁ ꢀꢁ ꢀꢁ ꢀꢁꢁ ꢀꢁꢂ ꢀꢁꢂ
ꢀRꢁꢂꢂ ꢃꢄꢅꢀꢆꢇꢈ ꢉꢃꢊ
ꢀꢁ ꢂꢃꢄ ꢅRRꢆR ꢇꢆꢈꢉꢊꢋꢅ ꢌꢍꢇꢎ
ꢀꢁꢂꢃꢁRꢄꢀꢅRꢁ ꢆꢇCꢈ
ꢀꢁꢂꢁ ꢃꢄꢀ
ꢀꢁꢂꢁ ꢃꢂꢄ
ꢀꢁꢂꢁ ꢃꢄꢅ
RT Programmed Switching
Frequency
PG High Thresholds
PG Low Thresholds
ꢀꢁ.ꢁ
ꢀ.ꢁ
ꢀ.ꢁ
ꢀ.ꢁ
ꢀ.ꢁ
ꢀ.ꢁ
ꢀ.ꢁ
ꢀ.ꢁ
ꢀ.ꢁ
250
225
200
175
150
125
100
75
ꢀꢁ.ꢂ
ꢀꢁ.ꢂ
ꢀꢁ.ꢂ
ꢀꢁ.ꢂ
ꢀꢁ.ꢂ
ꢀꢁ.ꢂ
ꢀꢁ.ꢂ
ꢀꢁ.ꢂ
ꢀꢁꢂ.ꢂ
ꢀꢁ Rꢂꢃꢂꢄꢅ
ꢀꢁ Rꢂꢃꢂꢄꢅ
ꢀꢁ ꢀꢂꢃꢃꢄꢅꢆ
ꢀꢁ ꢀꢂꢃꢃꢄꢅꢆ
50
25
0
ꢀꢁꢂ ꢀꢁꢂ
ꢀ
ꢀꢁ ꢀꢁ ꢀꢁ ꢀꢁꢁ ꢀꢁꢂ ꢀꢁꢂ
0.2 0.6
1.4 1.8 2.2 2.6
3
1
ꢀꢁꢂ ꢀꢁꢂ
ꢀ
ꢀꢁ ꢀꢁ ꢀꢁ ꢀꢁꢁ ꢀꢁꢂ ꢀꢁꢂ
ꢀꢁꢂꢃꢁRꢄꢀꢅRꢁ ꢆꢇCꢈ
ꢀꢁꢂꢃꢁRꢄꢀꢅRꢁ ꢆꢇCꢈ
SWITCHING FREQUENCY (MHz)
ꢀꢁꢂꢁ ꢃꢂꢄ
ꢀꢁꢂꢁ ꢃꢂꢄ
8636 G33
Minimum Input Voltage
Bias Pin Current
Bias Pin Current
ꢀ.ꢁ
ꢀ.ꢁ
ꢀ.ꢁ
ꢀ.ꢁ
ꢀ.ꢁ
ꢀ.ꢁ
ꢀ.ꢀ
ꢀ.ꢁ
ꢀ.ꢁ
ꢀ.ꢁ
ꢀ.ꢁ
ꢀ.ꢁ
ꢀ.ꢁ
ꢀ.ꢁ
ꢀꢁ
ꢀꢁ
ꢀꢁ
ꢀꢁ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ ꢁꢂ
ꢀꢁꢂꢃ
ꢀꢁꢂ
ꢀꢁ
ꢀ ꢁꢂ
ꢀ ꢁꢂꢃ
ꢀ ꢁꢂ
ꢀ
ꢀꢁꢂꢃ
ꢀ
ꢀ ꢁꢂ
ꢀ ꢁꢂ
ꢀ ꢁꢂ
ꢀꢁꢂꢃ
ꢀꢁꢂ
ꢀ
ꢀ
ꢀ
ꢀꢁꢂꢃ
ꢀ ꢁꢂꢃꢄ
ꢀꢁ
ꢀ
ꢀ
ꢀꢁ ꢀꢁ ꢀꢁ ꢀꢁ ꢀꢁ ꢀꢁ ꢀꢁ ꢀꢁ
ꢀꢁꢂꢃꢄ ꢅꢆꢇꢄꢈꢉꢊ ꢋꢅꢌ
ꢀꢁꢂ ꢀꢁꢂ
ꢀ
ꢀꢁ
ꢀꢁ
ꢀꢁ ꢀꢁꢁ ꢀꢁꢂ
ꢀ.ꢁ ꢀ.ꢁ
ꢀ
ꢀ.ꢁ ꢀ.ꢁ ꢀ.ꢀ ꢀ.ꢁ ꢀ.ꢁ
ꢀꢁꢂꢃꢁRꢄꢀꢅRꢁ ꢆꢇCꢈ
ꢀꢁꢂꢃCꢄꢂꢅꢆ ꢇRꢈꢉꢊꢈꢅCꢋ ꢌꢍꢄꢎꢏ
ꢀꢁꢂꢁ ꢃꢂꢄ
ꢀꢁꢂꢁ ꢃꢂꢄ
ꢀꢁꢂꢁ ꢃꢂꢁ
Rev. C
8
For more information www.analog.com
LT8636/LT8637
TYPICAL PERFORMANCE CHARACTERISTICS
Case Temperature Rise vs 7A
Pulsed Load
Switching Rising Edge
Case Temperature Rise
ꢀꢁꢂ
ꢀꢁꢂ
ꢀꢁꢂ
ꢀꢁ
ꢀꢁ
ꢀꢁ
ꢀꢁ
ꢀꢁ
ꢀꢁ
ꢀ
ꢀꢁ
ꢀꢁ
ꢀꢁ
ꢀꢁ
ꢀꢁ
ꢀꢁ
ꢀꢁ
ꢀꢁ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ ꢁꢂꢃꢄ ꢅ ꢀ ꢁꢂꢃꢄ
ꢀCꢁꢂꢃꢄꢅ ꢀꢆꢇꢈ ꢉꢈꢅRꢀ
ꢀꢁ
ꢀꢁ
ꢀꢁ
ꢀꢁ
ꢀꢁ
ꢀ ꢁꢂꢃꢄ ꢅ ꢀ ꢁꢂꢃꢄ
ꢀ
ꢀ ꢁꢂꢃ
ꢀꢁ
ꢀꢁ
ꢀꢁꢂ
ꢀ ꢁꢂꢃꢄ
ꢀꢁ
ꢀꢁꢂꢃꢄꢅꢆ ꢇꢈꢂꢄ ꢉ ꢊ.ꢋꢌꢂ
ꢀꢁꢂꢃ ꢄꢅꢆꢇꢈꢉ ꢆꢊꢋꢉ ꢌ ꢍꢋ
ꢀ ꢁꢂꢃꢄ ꢅ ꢀ ꢁꢂꢃꢄ
ꢀ
ꢀ
ꢀ ꢁꢂ
ꢀꢁ
ꢀ ꢁꢂꢃꢄ ꢅ ꢀ ꢁꢂꢃꢄ
ꢀꢁ
ꢀꢁꢂꢃ ꢄꢃꢅRꢀ ꢆꢇ ꢈꢉꢆꢊꢊ ꢅꢆR
ꢀ ꢁ ꢂꢃꢀꢄꢅꢆꢅꢇ ꢈ.ꢉꢊꢋ
ꢀ
ꢀꢁ
ꢀꢁꢂꢃꢄꢁ
ꢀꢁꢂꢁ ꢃꢂꢄ
ꢀꢁꢂꢃꢄꢅꢆ
ꢀ
ꢀꢁꢂꢃ
ꢀ ꢁꢂꢃ
ꢀꢁ
ꢀ
ꢀ ꢁꢂ
ꢀ
ꢀ.ꢁ
ꢀ.ꢁ
ꢀ.ꢁ
ꢀ.ꢁ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀꢁꢂꢃ CꢃCꢄꢅ ꢆꢇ ꢈꢉ ꢄꢆꢉꢀ
ꢀꢁꢂꢃ CꢄRRꢅꢆꢇ ꢈꢂꢉ
ꢀꢁꢂꢁ ꢃꢂꢀ
ꢀꢁꢂꢁ ꢃꢂꢄ
Switching Waveforms, Full
Frequency Continuous Operation
Switching Waveforms, Burst
Mode Operation
Switching Waveforms
ꢀ
ꢀ
ꢀ
ꢀ
ꢀꢁꢂꢃꢄꢅ
ꢀ
ꢀ
ꢀꢁꢂꢃꢄꢅ
ꢀꢁꢁꢂꢃꢄꢅꢆꢇ
ꢀ
ꢀꢁ
ꢀ
ꢀꢁ
ꢀꢁꢂꢃꢄꢁ
ꢀ
ꢀꢁ
ꢀꢁꢂꢃꢄꢁ
ꢀꢁꢂꢃꢄꢅꢂ
ꢀꢁꢂꢁ ꢃꢄꢅ
ꢀꢁꢂꢁ ꢃꢄꢅ
ꢀꢁꢂꢁ ꢃꢄꢅ
ꢀꢁꢁꢂꢃꢄꢅꢆꢇ
ꢀꢁꢂꢃꢄꢅꢆ
ꢀꢁꢁꢂꢃꢄꢅꢆꢇ
ꢀRꢁꢂꢃ ꢄꢅꢆꢇ ꢅꢄꢄꢈꢉCꢅꢃꢉꢁꢂ
ꢀRꢁꢂꢃ ꢄꢅꢆꢇ ꢅꢄꢄꢈꢉCꢅꢃꢉꢁꢂ
ꢀRꢁꢂꢃ ꢄꢅꢆꢇ ꢅꢄꢄꢈꢉCꢅꢃꢉꢁꢂ
ꢀꢁꢂ ꢀꢁ ꢂꢃ
ꢀꢁ ꢂꢀ
ꢀꢁꢂ ꢀꢁ ꢂꢃ
ꢀꢁ ꢂꢃꢄꢀ
ꢀꢁ
ꢀꢁꢂ
ꢀꢁꢂ ꢀꢁ ꢂꢃ
ꢀꢁ ꢂꢀ
ꢀꢁ
ꢀꢁꢂ
ꢀꢁ
ꢀꢁꢂ
ꢀ
ꢀ ꢁꢂ
ꢀꢁꢂC
LT8637 Transient Response;
External Compensation
LT8636 Transient Response;
Internal Compensation
ꢀ
ꢀ
ꢀꢁꢂꢃ
ꢀꢁꢂꢃ
ꢀꢁꢂꢃꢄꢅ
ꢀꢁꢂꢃꢄꢅ
ꢀ
ꢀꢁꢂ
ꢀ
ꢀꢁꢂ
ꢀꢁꢁꢂꢃꢄꢅꢆꢃ
ꢀꢁꢁꢂꢃꢄꢅꢆꢃ
ꢀꢁꢂꢁ ꢃꢄꢂ
ꢀꢁꢂꢁ ꢃꢄꢄ
ꢀꢁꢂꢃꢄꢅꢆꢇ
ꢀꢁꢂꢃꢄꢅꢆꢇ
ꢀRꢁꢂꢃ ꢄꢅꢆꢇ ꢅꢄꢄꢈꢉCꢅꢃꢉꢁꢂ
ꢀꢁ ꢂꢃ ꢄꢁ ꢂRꢁꢅꢆꢇꢈꢅꢂ
ꢀꢁꢂ ꢀ ꢁꢂ
ꢀꢁ ꢂꢃ ꢄꢁ ꢂRꢁꢅꢆꢇꢈꢅꢂ
ꢀꢁꢂ ꢀ ꢁꢂ
ꢀꢁ
ꢀꢁꢂ
ꢀ
C
C
ꢀ ꢁꢂꢃꢄ
ꢀꢁ
ꢀꢁꢂ
ꢀꢁ
ꢀ
ꢀ ꢁꢂꢃꢄ
ꢀ ꢁꢁꢂꢃꢄꢅ R ꢀ ꢁ.ꢂꢃꢄ
C
ꢀꢁ
C
ꢀꢁꢂ
C
ꢀ ꢁꢂꢂꢃꢄꢅ C
ꢀ ꢁꢂꢃꢄ
ꢀ ꢁꢂꢂꢃꢄꢅ C
ꢀ ꢁ.ꢂꢃꢄ
ꢀꢁꢂ
ꢀꢁꢂꢃ
ꢀꢁꢂꢃ
Rev. C
9
For more information www.analog.com
LT8636/LT8637
TYPICAL PERFORMANCE CHARACTERISTICS
LT8636 Transient Response;
100mA to 1.1A Transient
LT8637 Transient Response;
100mA to 1.1A Transient
ꢀ
ꢀ
ꢀꢁꢂꢃ
ꢀꢁꢂꢃ
ꢀꢁꢂꢃꢄꢅ
ꢀꢁꢂꢃꢄꢅ
ꢀꢁꢂꢃꢄ ꢅꢆꢇe ꢈꢉꢊRꢋꢌꢍꢈꢎ
ꢀꢁꢂꢃꢄ ꢅꢆꢇe ꢈꢉꢊRꢋꢌꢍꢈꢎ
ꢀ
ꢀꢁꢂ
ꢀ
ꢀꢁꢂ
ꢀꢁꢁꢂꢃꢄꢅꢆꢃ
ꢀꢁꢁꢂꢃꢄꢅꢆꢃ
ꢀCꢁ
ꢀCꢁ
ꢀꢁꢂꢁ ꢃꢄꢁ
ꢀꢁꢂꢁ ꢃꢄꢅ
ꢀꢁꢂꢃꢄꢅꢆꢇ
ꢀꢁꢂꢃꢄꢅꢆꢇ
C
ꢀ ꢁꢁꢂꢃꢄꢅ R ꢀ ꢁ.ꢂꢃꢄꢅ C
ꢀ ꢁ.ꢂꢃꢄ
ꢀꢁꢂꢃ
ꢀRꢁꢂꢃ ꢄꢅꢆꢇ ꢅꢄꢄꢈꢉCꢅꢃꢉꢁꢂ
ꢀꢁꢁꢂꢃ ꢄꢅ ꢀ.ꢀꢃ ꢄRꢃꢆꢇꢈꢉꢆꢄ
ꢀꢁꢂ ꢀ ꢁꢂ ꢀ ꢁ ꢀ ꢁꢂꢃꢄ
C
C
ꢀꢁꢁꢂꢃ ꢄꢅ ꢀ.ꢀꢃ ꢄRꢃꢆꢇꢈꢉꢆꢄ
ꢀꢁꢂ ꢀ ꢁꢂ ꢀ ꢁ ꢀ ꢁꢂꢃꢄ
C
ꢀꢁ ꢀꢁꢂ ꢀꢁ
ꢀ ꢁꢂꢂꢃꢄ
ꢀꢁ
ꢀꢁꢂ ꢀꢁ
C
ꢀ ꢁꢂꢂꢃꢄ
ꢀꢁꢂ
ꢀꢁꢂ
Start-Up Dropout Performance
Start-Up Dropout Performance
V
V
IN
IN
V
V
IN
IN
2V/DIV
2V/DIV
V
V
OUT
OUT
V
V
OUT
2V/DIV
OUT
2V/DIV
8636 G47
8636 G48
100ms/DIV
100ms/DIV
2.5Ω LOAD
(2A IN REGULATION)
20Ω LOAD
(250mA IN REGULATION)
Rev. C
10
For more information www.analog.com
LT8636/LT8637
TYPICAL PERFORMANCE CHARACTERISTICS
Conducted EMI Performance
ꢀꢁ
ꢀꢁ
ꢀꢁ
ꢀꢁ
ꢀꢁ
ꢀꢁ
ꢀ
ꢀꢁꢂ
ꢀꢁꢂ
ꢀꢁRꢂꢃꢄ ꢀꢁꢂCꢅRꢆꢇ ꢇꢈꢄꢂ
ꢀꢁꢂꢃꢄ ꢀRꢃꢅꢆꢃꢇCꢈ ꢉꢊꢄꢃ
ꢀꢁꢂ
ꢀꢁꢂ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀꢁ
ꢀꢁ
ꢀꢁ
ꢀꢁ ꢀꢁ ꢀꢁ
ꢀꢁ
ꢀRꢁꢂꢃꢁꢄCꢅ ꢆꢇꢈꢉꢊ
ꢀꢁꢂꢁ ꢃꢄꢅ
ꢀCꢁꢂꢃꢄꢅ ꢀꢆꢇꢈ ꢉꢈꢅRꢀ
ꢀꢁꢂꢃꢄ ꢅꢆꢂ ꢇꢂꢈꢃꢅR ꢂꢉꢊꢃꢋꢈꢈꢅꢌꢍ
ꢀꢁꢂ ꢃꢄꢅꢆꢇ ꢇꢈ ꢉꢂ ꢈꢆꢇꢅꢆꢇ ꢊꢇ ꢉꢊꢋ ꢌ ꢀ ꢁꢂꢃꢄ
ꢀꢁ
Radiated EMI Performance
(CISPR25 Radiated Emission Test with Class 5 Peak Limits)
ꢀꢁ
ꢀꢁRꢂꢃCꢄꢅ ꢆꢇꢅꢄRꢃꢈꢄꢂꢃꢇꢉ
ꢀꢁꢂꢃ ꢄꢁꢅꢁCꢅꢆR
ꢀꢁ
ꢀꢁ
ꢀꢁ
ꢀꢁ
ꢀꢁ
ꢀꢁ
ꢀꢁ
ꢀꢁ
ꢀ
Cꢀꢁꢂꢂ ꢃ ꢄꢅꢁꢆ ꢀꢇꢈꢇꢉ
ꢀꢁRꢂꢃꢄ ꢀꢁꢂCꢅRꢆꢇ ꢇꢈꢄꢂ
ꢀꢁꢂꢃꢄ ꢀRꢃꢅꢆꢃꢇCꢈ ꢉꢊꢄꢃ
ꢀ
ꢀꢁ
ꢀ
ꢀꢁꢁ
ꢀꢁꢁ
ꢀꢁꢁ
ꢀꢁꢁ
ꢀꢁꢁ
ꢀꢁꢁ
ꢀꢁꢁ
ꢀꢁꢁ
ꢀꢁꢁ ꢀꢁꢁꢁ
ꢀRꢁꢂꢃꢁꢄCꢅ ꢆꢇꢈꢉꢊ
ꢀꢁꢂꢁ ꢃꢄꢅ
ꢀCꢁꢂꢃꢄꢅ ꢀꢆꢇꢈ ꢉꢈꢅRꢀ
ꢀꢁꢂꢃꢄ ꢅꢆꢂ ꢇꢂꢈꢃꢅR ꢂꢉꢊꢃꢋꢈꢈꢅꢌꢍ
ꢀꢁꢂ ꢃꢄꢅꢆꢇ ꢇꢈ ꢉꢂ ꢈꢆꢇꢅꢆꢇ ꢊꢇ ꢉꢊꢋ ꢌ ꢀ ꢁꢂꢃꢄ
ꢀꢁ
Rev. C
11
For more information www.analog.com
LT8636/LT8637
PIN FUNCTIONS
PG (Pin 1): The PG pin is the open-drain output of an
internal comparator. PG remains low until the FB pin is
within 8% of the final regulation voltage, and there are
no fault conditions. PG is also pulled low when EN/UV is
BST (Pin 7): 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.
below 1V, INTV has fallen too low, V is too low, or
CC
IN
SW (Pins 8–10): The SW pins are the outputs of the inter-
nal power switches. Tie these pins together and connect
them to the inductor. This node should be kept small on
the PCB for good performance and low EMI.
thermal shutdown. PG is valid when V is above 3.4V.
IN
BIAS (Pin 2): The internal regulator will draw current from
BIAS instead of V when BIAS is tied to a voltage higher
IN
than 3.1V. For output voltages of 3.3V to 25V this pin
EN/UV (Pin 14): The LT8636/LT8637 is shut down when
this pin is low and active when this pin is high. The hyster-
etic threshold voltage is 1.00V going up and 0.96V going
should be tied to V . If this pin is tied to a supply other
OUT
than V
use a 1µF local bypass capacitor on this pin.
OUT
If no supply is available, tie to GND. However, especially
for high input or high frequency applications, BIAS should
be tied to output or an external supply of 3.3V or above.
down. Tie to V if the shutdown feature is not used. An
IN
external resistor divider from V can be used to program
IN
a V threshold below which the LT8636/LT8637 will shut
IN
INTV (Pin 3): Internal 3.4V Regulator Bypass Pin. The
down.
CC
internal power drivers and control circuits are powered
SYNC/MODE (Pin 15): For the LT8636/LT8637, this
pin programs four different operating modes: 1) Burst
Mode operation. Tie this pin to ground for Burst Mode
operation at low output loads—this will result in ultralow
quiescent current. 2) Forced Continuous mode (FCM).
This mode offers fast transient response and full
frequency operation over a wide load range. Float this
pin for FCM. When floating, pin leakage currents should
be <1µA. See Block Diagram for internal pull-up and
pull-down resistance. 3) Spread spectrum mode. Tie
from this voltage. INTVCC maximum output current is
20mA. Do not load the INTV pin with external circuitry.
CC
INTV current will be supplied from BIAS if BIAS > 3.1V,
CC
otherwise current will be drawn from VIN. Voltage on
INTVCC will vary between 2.8V and 3.4V when BIAS is
between 3.0V and 3.6V. Place a low ESR ceramic capaci-
tor of at least 1µF from this pin to ground close to the IC.
GND (Pins 4, 13, Exposed Pad Pin 21): Ground. Place
the negative terminal of the input capacitor as close to
the GND pins as possible. The exposed pads should be
soldered to the PCB for good thermal performance. If
necessary due to manufacturing limitations Pin 21 may
be left disconnected, however thermal performance will
be degraded.
this pin high to INTV (~3.4V) or an external supply
CC
of 3V to 4V for forced continuous mode with spread-
spectrum modulation. 4) Synchronization mode. Drive
this pin with a clock source to synchronize to an external
frequency. During synchronization the part will operate
in forced continuous mode.
NC (Pins 5, 12): No Connect. This pin is not connected
to internal circuitry and can be tied anywhere on the PCB,
typically ground.
CLKOUT (Pin 16): In forced continuous mode, spread
spectrum, and synchronization modes, the CLKOUT pin
will provide a ~200ns wide pulse at the switch frequency.
The low and high levels of the CLKOUT pin are ground and
INTVCC respectively, and the drive strength of the CLKOUT
pin is several hundred ohms. In Burst Mode operation,
the CLKOUT pin will be low. Float this pin if the CLKOUT
function is not used.
VIN (Pins 6, 11): The VIN pins supply current to the
LT8636/LT8637 internal circuitry and to the internal top-
side power switch. The LT8636/LT8637 requires the use
of multiple V bypass capacitors. Two small 1µF capaci-
IN
tors should be placed as close as possible to the LT8636/
LT8637, one capacitor on each side of the device (C
,
IN1
C
). A third capacitor with a larger value, 2.2µF or higher,
RT (Pin 17): A resistor is tied between RT and ground to
set the switching frequency.
IN2
should be placed near CIN1 or CIN2. See Applications
Information section for sample layout.
Rev. C
12
For more information www.analog.com
LT8636/LT8637
PIN FUNCTIONS
TR/SS (Pin 18): Output Tracking and Soft-Start Pin. This
pin allows user control of output voltage ramp rate dur-
ing start-up. For the LT8636/LT8637, a TR/SS voltage
below 0.97V forces it 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. For the LT8637,
a TR/SS voltage below 1.6V forces it to regulate the FB
pin to a function of the TR/SS pin voltage. See plot in
the Typical Performance Characteristics section. When
TR/SS is above 1.6V, the tracking function is disabled
and the internal reference resumes control of the error
FB (Pin 19, LT8636 Only): The LT8636/LT8637 regu-
lates the FB pin to 0.970V. Connect the feedback resistor
divider tap to this pin. Also, connect a phase lead capaci-
tor between FB and V . Typically, this capacitor is 4.7pF
OUT
to 22pF.
V (Pin 19, LT8637 Only): The V pin is the output of the
C
C
internal error amplifier. The voltage on this pin controls
the peak switch current. Tie an RC network from this pin
to ground to compensate the control loop.
FB (Pin 20): The LT8636/LT8637 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
amplifier. An internal 1.9µA pull-up current from INTV
CC
V
. Typically, this capacitor is 4.7pF to 22pF.
OUT
on this pin allows a capacitor to program output voltage
slew rate. This pin is pulled to ground with an internal
200Ω 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.
Corner Pins: These pins are for mechanical support only
and can be tied anywhere on the PCB, typically ground.
Rev. C
13
For more information www.analog.com
LT8636/LT8637
BLOCK DIAGRAM
ꢔ
ꢍꢎ
ꢝꢝ
ꢔ
ꢍꢎ
C
ꢍꢎꢖ
ꢔ
ꢁ
ꢍꢎ
C
ꢍꢎꢂ
ꢍꢎꢏꢋRꢎꢐꢈ ꢑ.ꢒꢓꢔ Rꢋꢕ
ꢇꢘꢄꢎ
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ꢅ
C
ꢍꢎꢝ
ꢃꢍꢐꢇ
ꢂ.ꢛꢔ
Rꢋꢜ
ꢖ
ꢂ
Rꢂ
ꢝꢔ
ꢅ
ꢆ
ꢉꢊꢏ
ꢋꢎꢡꢚꢔ
ꢝꢛ
ꢍꢎꢏꢔ
CC
Rꢛ
ꢉꢊꢏ
ꢇꢈꢉꢊꢋ Cꢉꢌꢊ
ꢉꢇCꢍꢈꢈꢐꢏꢉR
C
ꢔCC
ꢈꢏꢀꢁꢂꢓ ꢉꢎꢈꢥ
ꢔ
C
ꢝꢒ
ꢝ
ꢖꢑꢑꢗꢘꢙ ꢏꢉ ꢂꢌꢘꢙ
R
C
C
ꢕ
ꢋRRꢉR
ꢐꢌꢊ
ꢊꢜ
ꢃꢇꢏ
ꢀꢠ
C
ꢓ
C
ꢔ
C
ꢅ
ꢅ
ꢆ
ꢃꢚRꢇꢏ
ꢄꢋꢏꢋCꢏ
ꢔ
ꢉꢚꢏ
C
ꢃꢇꢏ
ꢈ
ꢌꢝ
ꢌꢖ
ꢇꢞ
ꢇꢘꢄꢎ
ꢀꢆꢝꢑ
ꢇꢞꢍꢏCꢘ ꢈꢉꢜꢍC
ꢐꢎꢄ
ꢐꢎꢏꢍꢟꢇꢘꢉꢉꢏ
ꢏꢘRꢉꢚꢜꢘ
ꢈꢏꢀꢁꢂꢁ
ꢉꢎꢈꢥ
Cꢝ Rꢝ
Rꢖ
ꢏꢘꢋRꢌꢐꢈ ꢇꢘꢄꢎ
ꢔ
ꢉꢚꢏ
ꢍꢎꢏꢔ ꢚꢔꢈꢉ
CC
C
ꢔ
ꢍꢎ
ꢚꢔꢈꢉ
ꢉꢚꢏ
ꢕꢃ
ꢖꢑ
ꢇꢘꢄꢎ
ꢏꢘꢋRꢌꢐꢈ ꢇꢘꢄꢎ
ꢚꢔꢈꢉ
C
ꢇꢇ
ꢉꢊꢏ
ꢝ.ꢒꢤꢐ
ꢔ
ꢍꢎ
ꢏRꢡꢇꢇ
Rꢏ
ꢜꢎꢄ
ꢛꢢ ꢝꢂꢢ ꢖꢝ
ꢝꢀ
ꢝꢓ
R
ꢏ
ꢍꢎꢏꢔ
CC
ꢁꢑꢗ
Cꢈꢣꢉꢚꢏ
ꢇꢥꢎCꢡꢌꢉꢄꢋ
ꢝꢁ
ꢝꢦ
ꢁꢑꢑꢗ
ꢀꢁꢂꢁ ꢃꢄ
Rev. C
14
For more information www.analog.com
LT8636/LT8637
OPERATION
The LT8636/LT8637 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
the oscillator operates continuously and positive SW tran-
sitions are aligned to the clock. Negative inductor current
is allowed. The LT8636/LT8637 can sink current from the
output and return this charge to the input in this mode,
improving load step transient response.
To improve EMI, the LT8636/LT8637 can operate in spread
spectrum mode. This feature varies the clock with a trian-
gular frequency modulation of +20%. For example, if the
LT8636/LT8637’s frequency is programmed to switch at
2MHz, spread spectrum mode will modulate the oscillator
between 2MHz and 2.4MHz. The SYNC/MODE pin should
be tied high to INTVCC (~3.4V) or an external supply of 3V
to 4V to enable spread spectrum modulation with forced
continuous mode.
by comparing the voltage on the V pin with an inter-
FB
nal 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 volt-
age 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 10A flowing through the
bottom switch, the next clock cycle will be delayed until
switch current returns to a safe level.
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 V . The BIAS pin should be connected to
IN
V
if the LT8636/LT8637 output is programmed at 3.3V
OUT
to 25V.
If the EN/UV pin is low, the LT8636/LT8637 is shut down
and draws 1µA from the input. When the EN/UV pin is
above 1V, the switching regulator will become active.
The VC pin optimizes the loop compensation of the
switching regulator based on the programmed switch-
ing frequency, allowing for a fast transient response. The
VC pin also enables current sharing and a CLKOUT pin
enables synchronizing other regulators to the LT8637.
To optimize efficiency at light loads, the LT8636/LT8637
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 (LT8636) or 230µA (LT8637 with BIAS
= 0). In a typical application, 2.5µA (LT8636) or 120µA
(LT8637 with BIAS = 5V ) will be consumed from the
input supply when reguOlaUtiTng with no load. The SYNC/
MODE pin is tied low to use Burst Mode operation and can
be floated to use forced continuous mode (FCM). If a clock
is applied to the SYNC/MODE pin, the part will synchronize
to an external clock frequency and operate in FCM.
Comparators monitoring the FB pin voltage will pull the PG
pin low if the output voltage varies more than 8% (typi-
cal) from the set point, or if a fault condition is present.
The oscillator reduces the LT8636/LT8637’s operating
frequency when the voltage at the FB pin 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 condi-
tions. When a clock is applied to the SYNC/MODE pin, the
SYNC/MODE pin is floated, or held DC high, the frequency
foldback is disabled and the switching frequency will slow
down only during overcurrent conditions.
The LT8636/LT8637 can operate in forced continuous
mode (FCM) for fast transient response and full fre-
quency operation over a wide load range. When in FCM
Rev. C
15
For more information www.analog.com
LT8636/LT8637
APPLICATIONS INFORMATION
Low EMI PCB Layout
Note that large, switched currents flow in the LT8636/
LT8637 V and GND pins and the input capacitors. The
IN
The LT8636/LT8637 is specifically designed to minimize
EMI emissions and also to maximize efficiency when
switching at high frequencies. For optimal performance
the LT8636/LT8637 requires the use of multiple VIN
bypass capacitors.
loops formed by the input capacitors should be as small
as possible by placing the capacitors adjacent to the V
IN
and GND pins. Capacitors with small case size such as
0603 are optimal due to lowest parasitic inductance.
The input capacitors, along with the inductor and out-
put capacitors, should be placed on the same side of the
circuit board, and their connections should be made on
that layer. Place a local, unbroken ground plane under the
application circuit on the layer closest to the surface layer.
The SW and BOOST nodes should be as small as possible.
Finally, keep the FB and RT nodes small so that the ground
traces will shield them from the SW and BOOST nodes.
Two small 1µF capacitors should be placed as close as
possible to the LT8636/LT8637, one capacitor on each
side of the device (C , C ). A third capacitor with a
IN1 IN2
larger value, 2.2µF or higher, should be placed near C
IN1
or C
.
IN2
See Figure 1 for recommended PCB layouts.
For more detail and PCB design files refer to the Demo
Board guide for the LT8636/LT8637.
C
C
R
ꢔ
R
ꢔ
C
ꢒ
C
ꢒ
C
C
R
C
ꢄꢄ
R
R
ꢁ
ꢄꢄ
ꢐ
C
ꢁ
R
R
ꢒ
ꢒ
C
C
ꢊCC
ꢊCC
C
C
ꢅꢇꢏ
ꢅꢇꢏ
C
C
ꢅꢇꢔ
C
C
ꢅꢇꢔ
ꢅꢇꢒ
ꢅꢇꢒ
C
C
ꢕꢄꢁ
ꢕꢄꢁ
ꢉ
ꢉ
C
C
ꢀꢋꢁ
ꢀꢋꢁ
ꢊ
ꢊꢅꢈ
ꢊ
ꢊꢅꢈ
ꢍꢎꢏꢎ ꢐꢑꢒꢓ
ꢊ
ꢊꢅꢈ
ꢊ ꢊꢅꢈ
ꢀꢋꢁ
ꢍꢎꢏꢎ ꢐꢑꢒꢓ
ꢆRꢀꢋꢇꢌ ꢊꢅꢈ
ꢀꢁꢂꢃR ꢄꢅꢆꢇꢈꢉ ꢊꢅꢈꢄ
ꢆRꢀꢋꢇꢌ ꢊꢅꢈ
ꢀꢁꢂꢃR ꢄꢅꢆꢇꢈꢉ ꢊꢅꢈꢄ
ꢅꢇ
ꢀꢋꢁ
ꢅꢇ
(a) LT8636
(b) LT8637
Figure 1. Recommended PCB Layouts for the LT8636
Rev. C
16
For more information www.analog.com
LT8636/LT8637
APPLICATIONS INFORMATION
While in Burst Mode operation the current limit of the top
switch is approximately 900mA (as shown in Figure 3),
resulting in low output voltage ripple. Increasing the out-
put capacitance will decrease output ripple proportion-
ally. As load ramps upward from zero the switching fre-
quency will increase but only up to the switching frequency
programmed by the resistor at the RT pin as shown in
Figure 2.
The exposed pads on the bottom of the package should be
soldered to the PCB to reduce thermal resistance to ambi-
ent. To keep thermal resistance low, extend the ground
plane from GND as much as possible, and add thermal
vias to additional ground planes within the circuit board
and on the bottom side.
Burst Mode Operation
To enhance efficiency at light loads, the LT8636/LT8637
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
LT8636/LT8637 delivers single small 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 LT8636 consumes 1.7µA, and the LT8637
consumes 230µA.
ꢀꢁꢂꢂ
ꢀꢁꢁꢁ
ꢀꢁꢁ
ꢀꢁꢁ
ꢀꢁꢁ
ꢀRꢁꢂꢃ ꢄꢅꢆꢇ ꢅꢄꢄꢈꢉCꢅꢃꢉꢁꢂ
ꢀꢁꢁ
ꢀ
ꢀ ꢁꢂꢃ
ꢀꢁ
ꢀ
ꢀ ꢁꢂ
ꢀꢁꢂ
ꢀ
As the output load decreases, the frequency of single cur-
rent pulses decreases (see Figure 2) and the percentage
of time the LT8636/LT8637 is in sleep mode increases,
ꢀ
ꢀꢁꢁ
ꢀꢁꢁ
ꢀꢁꢁ
ꢀꢁꢁ
ꢀꢁꢁ
ꢀꢁꢁ
ꢀꢁꢂꢃ CꢄRRꢅꢆꢇ ꢈꢉꢂꢊ
ꢀꢁꢂꢁ ꢃꢄꢅ
Figure 2. SW Frequency vs Load Information
in Burst Mode Operation
resulting in much higher light load efficiency than for typi
-
cal converters. By maximizing the time between pulses,
the LT8636/LT8637’s quiescent current approaches
2.5µA for a typical application when there is no output
load. Therefore, to optimize the quiescent current perfor-
mance at light loads, the current in the feedback resistor
divider must be minimized as it appears to the output as
load current.
ꢀ
ꢀ
ꢀꢁꢁꢂꢃꢄꢅꢆꢇ
ꢀ
ꢀꢁ
ꢀꢁꢂꢃꢄꢁ
In order to achieve higher light load efficiency, more
energy must be delivered to the output during the sin-
gle small pulses in Burst Mode operation such that the
LT8636/LT8637 can stay in sleep mode longer between
each pulse. This can be achieved by using a larger
value inductor (i.e., 4.7µH), and should be considered
independent of switching frequency when choosing
an inductor. For example, while a lower inductor value
would typically be used for a high switching frequency
application, if high light load efficiency is desired, a
higher inductor value should be chosen. See curve in
Typical Performance Characteristics.
ꢀꢁꢂꢁ ꢃꢄꢂ
ꢀꢁꢂꢃꢄꢅꢆ
ꢀRꢁꢂꢃ ꢄꢅꢆꢇ ꢅꢄꢄꢈꢉCꢅꢃꢉꢁꢂ
ꢀꢁꢂ ꢀꢁ ꢂꢃ
ꢀꢁꢂC
ꢀꢁ ꢂꢃꢄꢀ
ꢀꢁ
ꢀꢁꢂ
ꢀ
ꢀ ꢁꢂ
Figure 3. Burst Mode Operation
Rev. C
17
For more information www.analog.com
LT8636/LT8637
APPLICATIONS INFORMATION
The output load at which the LT8636/LT8637 reaches the
programmed frequency varies based on input voltage,
output voltage and inductor choice. To select low ripple
Burst Mode operation, tie the SYNC/MODE pin below 0.4V
(this can be ground or a logic low output).
FCM is disabled if the VIN pin is held above 37V or if the FB
pin is held greater than 8% above the feedback reference
voltage. FCM is also disabled during soft-start until the
soft-start capacitor is fully charged. When FCM is disabled
in these ways, negative inductor current is not allowed
and the LT8636/LT8637 operates in pulse-skipping mode.
Forced Continuous Mode
For robust operation over a wide V and V
range, use
OUT
IN
:
The LT8636/LT8637 can operate in forced continuous
mode (FCM) for fast transient response and full fre-
quency operation over a wide load range. When in FCM,
the oscillator operates continuously and positive SW
transitions are aligned to the clock. Negative inductor
current is allowed at light loads or under large tran-
sient conditions. The LT8636/LT8637 can sink current
from the output and return this charge to the input in
this mode, improving load step transient response (see
Figure 4). At light loads, FCM operation is less efficient
than Burst Mode operation, but may be desirable in
applications where it is necessary to keep switching
harmonics out of the signal band. FCM must be used if
the output is required to sink current. To enable FCM,
float the SYNC/MODE pin. Leakage current on this pin
should be <1µA. See Block Diagram for internal pull-up
and pull-down resistance.
an inductor value greater than L
MIN
⎛
⎞
VOUT
2 • fSW
VOUT
V
IN,MAX
LMIN
=
• 1–
⎜
⎟
⎝
⎠
Spread Spectrum Mode
The LT8636/LT8637 features spread spectrum opera-
tion to further reduce EMI emissions. To enable spread
spectrum operation, the SYNC/MODE pin should be tied
high to INTV (~3.4V)or an external supply of 3V to 4V.
CC
In this mode, triangular frequency modulation is used
to vary the switching frequency between the value pro-
grammed by RT to approximately 20% higher than that
value. The modulation frequency is approximately 3kHz.
For example, when the LT8636/LT8637 is programmed to
2MHz, the frequency will vary from 2MHz to 2.4MHz at a
3kHz rate. When spread spectrum operation is selected,
Burst Mode operation is disabled, and the part will run in
forced continuous mode.
ꢀ
ꢀꢁꢂꢃ
ꢀꢁꢂꢃꢄꢅ
Synchronization
ꢀꢁꢂꢃꢄ ꢅꢆꢇe ꢈꢉꢊRꢋꢌꢍꢈꢎ
To synchronize the LT8636/LT8637 oscillator to an exter-
nal frequency, connect a square wave to the SYNC/MODE
pin. The square wave amplitude should have valleys that
are below 0.4V and peaks above 1.5V (up to 6V) with a
minimum on-time and off-time of 50ns.
ꢀ
ꢀꢁꢂ
ꢀꢁꢁꢂꢃꢄꢅꢆꢃ
ꢀCꢁ
ꢀꢁꢂꢁ ꢃꢄꢅ
ꢀꢁꢂꢃꢄꢅꢆꢇ
ꢀRꢁꢂꢃ ꢄꢅꢆꢇ ꢅꢄꢄꢈꢉCꢅꢃꢉꢁꢂ
ꢀꢁꢁꢂꢃ ꢄꢅ ꢀ.ꢀꢃ ꢄRꢃꢆꢇꢈꢉꢆꢄ
ꢀꢁꢂ ꢅ ꢆꢂ ꢅ ꢊ ꢍ ꢀꢎꢏꢐ
ꢃꢄ
ꢀꢁꢂ
ꢇꢈꢉ ꢋꢌ
C
ꢀ ꢁꢂꢂꢃꢄ
Figure 4. LT8636 Load Step Transient Response with
and without Forced Continuous Mode
Rev. C
18
For more information www.analog.com
LT8636/LT8637
APPLICATIONS INFORMATION
The LT8636/LT8637 will not enter Burst Mode operation
at low output loads while synchronized to an external
clock, but instead will run forced continuous mode to
maintain regulation. The LT8636/LT8637 may be syn-
chronized over a 200kHz to 3MHz range. The RT resistor
should be chosen to set the LT8636/LT8637 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 sub-
harmonic oscillations is established by the inductor size,
input voltage and output voltage. Since the synchroniza-
tion frequency will not change the slopes of the inductor
current waveform, if the inductor is large enough to avoid
subharmonic oscillations at the frequency set by RT, then
the slope compensation will be sufficient for all synchro-
nization frequencies.
1M and R2 = 412k, the feedback divider draws 2.3µA.
With V = 12V and n = 80%, this adds 0.8µA to the 1.7µA
IN
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 V ; this is plotted in the
IN
Typical Performance Characteristics section.
When using large FB resistors, a 4.7pF to 22pF phase-lead
capacitor should be connected from V
to FB.
OUT
Setting the Switching Frequency
The LT8636/LT8637 uses a constant frequency PWM
architecture that can be programmed to switch from
200kHz to 3MHz by using a resistor tied from the RT pin
to ground. A table showing the necessary R value for a
T
desired switching frequency is in Table 1.
The R resistor required for a desired switching frequency
T
can be calculated using:
46.5
fSW
FB Resistor Network
RT =
–5.2
(3)
The output voltage is programmed with a resistor divider
between the output and the FB pin. Choose the resistor
values according to:
where R is in kΩ and f is the desired switching fre-
T
SW
quency in MHz.
VOUT
0.970V
⎛
⎜
⎝
⎞
⎠
Table 1. SW Frequency vs RT Value
R1=R2
–1
⎟
(1)
f
SW
(MHz)
0.2
0.3
0.4
0.5
0.6
0.7
0.8
1.0
1.2
1.4
1.6
1.8
2.0
2.2
3.0
R (kΩ)
T
232
150
Reference designators refer to the Block Diagram. 1%
resistors are recommended to maintain output voltage
accuracy.
110
88.7
71.5
60.4
52.3
41.2
33.2
28.0
23.7
20.5
17.8
15.8
10.7
For the LT8636/LT8637, 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:
⎛
⎞
VOUT
R1+R2
VOUT
1
⎝ ⎠
n
⎛
⎜
⎝
⎞
⎟
⎠
⎛ ⎞
I =1.7µA+
(2)
⎜ ⎟
Q
⎜
⎟
V
⎝
⎠
IN
where 1.7µA is the quiescent current of the LT8636/
LT8637 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 =
Rev. C
19
For more information www.analog.com
LT8636/LT8637
APPLICATIONS INFORMATION
Operating Frequency Selection and Trade-Offs
Inductor Selection and Maximum Output Current
The LT8636/LT8637 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 LT8636/LT8637 safely toler-
ates operation with a saturated inductor through the use
of a high speed peak-current mode architecture.
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 disadvan-
tages are lower efficiency and a smaller input voltage range.
The highest switching frequency (f
) for a given
SW(MAX)
A good first choice for the inductor value is:
application can be calculated as follows:
⎛
⎞
V
OUT + VSW(BOT)
V
OUT + VSW(BOT)
L =
• 0.7
(6)
⎜
⎟
fSW(MAX)
=
(4)
fSW
⎝
⎠
tON(MIN) V – VSW(TOP) + VSW(BOT)
IN
where fSW is the switching frequency in MHz, VOUT is
where V is the typical input voltage, V
is the output
OUT
voltage,INV
and V
are the internal switch
the output voltage, V
is the bottom switch drop
SW(BOT)
drops (~0S.4WV(,TO~P0).15V, rSeWsp(BeOcTti)vely at maximum load)
(~0.15V) and L is the inductor value in µH.
and t
is the minimum top switch on-time (see the
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.
ON(MIN)
Electrical Characteristics). This equation shows that a
slower switching frequency is necessary to accommodate
In addition, the saturation current (typically labeled I
)
a high V /V
ratio.
SAT
IN OUT
rating of the inductor must be higher than the load current
plus 1/2 of in inductor ripple current:
For transient operation, V may go as high as the abso-
IN
lute maximum rating of 42V regardless of the R value,
however the LT8636/LT8637 will reduce switchTing fre-
quency as necessary to maintain control of inductor cur-
rent to assure safe operation.
1
2
(7)
I
L(PEAK) =ILOAD(MAX) + ΔIL
where ∆I is the inductor ripple current as calculated in
L
The LT8636/LT8637 is capable of a maximum duty cycle
Equation 9 and I
for a given application.
is the maximum output load
LOAD(MAX)
of approximately 99%, and the V -to-V
dropout is
IN
OUT
limited by the R
of the top switch. In this mode the
DS(ON)
As a quick example, an application requiring 3A output
should use an inductor with an RMS rating of greater than
LT8636/LT8637 skips switch cycles, resulting in a lower
switching frequency than programmed by RT.
3A and an I
of greater than 4A. During long duration
overload orSsAhTort-circuit conditions, the inductor RMS
rating requirement is greater to avoid overheating of the
inductor. To keep the efficiency high, the series resistance
(DCR) should be less than 0.02Ω, and the core material
should be intended for high frequency applications.
For applications that cannot allow deviation from the pro-
grammed switching frequency at low V /V
ratios use
IN OUT
the following formula to set switching frequency:
V
OUT + VSW(BOT)
V
=
– VSW(BOT) + VSW(TOP) (5)
IN(MIN)
1– fSW •tOFF(MIN)
The LT8636/LT8637 limits the peak switch current in
order to protect the switches and the system from over-
where VIN(MIN) is the minimum input voltage without
skipped cycles, V
is the output voltage, V
and
SW(TOP)
V
are theOinUtTernal switch drops (~0.4V, ~0.15V,
load faults. The top switch current limit (I ) is 10A at
LIM
SW(BOT)
low duty cycles and decreases linearly to 7A at DC = 0.8.
The inductor value must then be sufficient to supply the
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.
desired maximum output current (I
), which is a
OUT(MAX)
function of the switch current limit (I ) and the ripple
LIM
current.
Rev. C
20
For more information www.analog.com
LT8636/LT8637
APPLICATIONS INFORMATION
For more information about maximum output current and
discontinuous operation, see Analog Devices Application
Note 44.
ΔIL
IOUT(MAX) =ILIM
–
(8)
2
The peak-to-peak ripple current in the inductor can be
calculated as follows:
For duty cycles greater than 50% (VOUT/VIN > 0.5), a
minimum inductance is required to avoid subharmonic
oscillation (See Equation 10). See Application Note 19
for more details.
⎛
⎞
VOUT
L•fSW
VOUT
V
IN(MAX)
ΔIL =
• 1–
⎜
⎟
(9)
⎝
⎠
(
)
2 •DC – 1
V
IN
L
=
(10)
MIN
where fSW is the switching frequency of the LT8636/
LT8637, and L is the value of the inductor. Therefore, the
maximum output current that the LT8636/LT8637 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 cur-
rent does not allow sufficient maximum output current
3.5 • f
SW
where DC is the duty cycle ratio (V /V ) and f is the
OUT IN
SW
switching frequency.
Input Capacitors
The V of the LT8636/LT8637 should be bypassed with at
IN
(I
) given the switching frequency, and maximum
inOpUuTt(vMoAlXta)ge used in the desired application.
least three ceramic capacitors for best performance. Two
small ceramic capacitors of 1µF should be placed close to
the part; one on each side of the device (CIN1, CIN2). These
capacitors should be 0402 or 0603 in size. For automotive
applications requiring 2 series input capacitors, two small
0402 or 0603 may be placed at each side of the LT8636/
In order to achieve higher light load efficiency, more
energy must be delivered to the output during the sin-
gle small pulses in Burst Mode operation such that the
LT8636/LT8637 can stay in sleep mode longer between
each pulse. This can be achieved by using a larger value
inductor (i.e., 4.7µH), and should be considered indepen-
dent of switching frequency when choosing an inductor.
For example, while a lower inductor value would typi-
cally be used for a high switching frequency application,
if high light load efficiency is desired, a higher inductor
value should be chosen. See curve in Typical Performance
Characteristics.
LT8637 near the V and GND pins.
IN
A third, larger ceramic capacitor of 2.2µF or larger should
be placed close to C or C . See layout section for
IN1
IN2
more detail. X7R or X5R capacitors are recommended for
best performance across temperature and input voltage
variations.
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.
The optimum inductor for a given application may dif-
fer 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 induc-
tor may be lower and the LT8636/LT8637 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.
A ceramic input capacitor combined with trace or cable
inductance forms a high quality (under damped) tank cir-
cuit. If the LT8636/LT8637 circuit is plugged into a live
supply, the input voltage can ring to twice its nominal
value, possibly exceeding the LT8636/LT8637’s voltage
rating. This situation is easily avoided (see Analog Devices
Application Note 88).
Rev. C
21
For more information www.analog.com
LT8636/LT8637
APPLICATIONS INFORMATION
Output Capacitor and Output Ripple
A final precaution regarding ceramic capacitors concerns
the maximum input voltage rating of the LT8636/LT8637.
As previously mentioned, a ceramic input capacitor com-
bined with trace or cable inductance forms a high quality
(underdamped) tank circuit. If the LT8636/LT8637 circuit
is plugged into a live supply, the input voltage can ring to
twice its nominal value, possibly exceeding the LT8636/
LT8637’s rating. This situation is easily avoided (see
Analog Devices Technology Application Note 88).
The output capacitor has two essential functions. Along
with the inductor, it filters the square wave generated by
the LT8636/LT8637 to produce the DC output. In this role
it determines the output ripple, thus low impedance at the
switching frequency is important. The second function is
to store energy in order to satisfy transient loads and sta-
bilize the LT8636/LT8637’s control loop. Ceramic capaci-
tors have very low equivalent series resistance (ESR) and
provide the best ripple performance. For good starting
values, see the Typical Applications section.
Enable Pin
The LT8636/LT8637 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 V if the shutdown feature is
not used, or tied to a logicIlNevel if shutdown control is
required.
Use X5R or X7R types. This choice will provide low out-
put ripple and good transient response. Transient perfor-
mance can be improved with a higher value output capaci-
tor and the addition of a feedforward capacitor placed
between V
and FB. Increasing the output capacitance
OUT
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.
Adding a resistor divider from V to EN programs the
IN
LT8636/LT8637 to regulate the output only when V is
IN
above a desired voltage (see the Block Diagram). Typically,
this threshold, V
, is used in situations where the
IN(EN)
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
When choosing a capacitor, special attention should be
given to the data sheet to calculate the effective capaci-
tance under the relevant operating conditions of voltage
bias and temperature. A physically larger capacitor or one
with a higher voltage rating may be required.
V
threshold prevents the regulator from operating
IN(EN)
Ceramic Capacitors
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:
Ceramic capacitors are small, robust and have very
low ESR. However, ceramic capacitors can cause prob-
lems when used with the LT8636/LT8637 due to their
piezoelectric nature. When in Burst Mode operation, the
LT8636/LT8637’s switching frequency depends on the
load current, and at very light loads the LT8636/LT8637
can excite the ceramic capacitor at audio frequencies,
generating audible noise. Since the LT8636/LT8637 oper-
ates at a lower current limit during Burst Mode opera-
tion, 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.
R3
R4
⎛
⎞
⎠
V
=
+1 •1.0V
(11)
⎜
⎝
⎟
IN(EN)
where the LT8636/LT8637 will remain off until VIN is
above V . Due to the comparator’s hysteresis, switch-
IN(EN)
ing will not stop until the input falls slightly below VIN(EN)
.
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 LT8636/LT8637. Therefore, the VIN(EN) resistors
should be large to minimize their effect on efficiency at
low loads.
Rev. C
22
For more information www.analog.com
LT8636/LT8637
APPLICATIONS INFORMATION
INTV Regulator
Figure 5 shows an equivalent circuit for the LT8637
control loop. The error amplifier is a transconductance
amplifier with finite output impedance. The power section,
consisting of the modulator, power switches, and inductor,
is modeled as a transconductance amplifier generating an
CC
An internal low dropout (LDO) regulator produces the 3.4V
supply from V that powers the drivers and the internal
IN
bias circuitry. The INTV can supply enough current for
CC
the LT8636/LT8637’s circuitry and must be bypassed to
ground with a minimum of 1µF ceramic capacitor. Good
bypassing is necessary to supply the high transient cur-
rents required by the power MOSFET gate drivers. To
improve efficiency the internal LDO can also draw cur-
rent 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 LT8636/LT8637, or can be tied to an external supply of
3.3V or above. If BIAS is connected to a supply other than
output current proportional to the voltage at the V pin.
C
Note that the output capacitor integrates this current, and
that the capacitor on the V pin (C ) integrates the error
C
C
amplifier output current, resulting in two poles in the loop.
A zero is required and comes from a resistor R in series
C
with C . This simple model works well as long as the value
of theCinductor is not too high and the loop crossover
frequency is much lower than the switching frequency. A
phase lead capacitor (C ) across the feedback divider can
be used to improve thePtrLansient response and is required
to cancel the parasitic pole caused by the feedback node
to ground capacitance.
V
, be sure to bypass with a local ceramic capacitor. If
OUT
the BIAS pin is below 3.0V, the internal LDO will consume
current from V . Applications with high input voltage and
IN
high switching frequency where the internal LDO pulls cur-
rent from V will increase die temperature because of the
IN
ꢓꢋꢔꢕꢖꢇ
higher power dissipation across the LDO. Do not connect
CꢈRRꢉꢊꢋ ꢌꢍꢎꢉ
ꢏꢍꢐꢉR ꢅꢋꢑꢒꢉ
an external load to the INTV pin.
CC
Frequency Compensation (LT8637 Only)
ꢌꢆ
ꢍꢈꢋꢏꢈꢋ
Loop compensation determines the stability and transient
performance, and is provided by the components tied to
ꢌꢜ
C
ꢏꢓ
Rꢆ
Rꢜ
ꢁ
ꢃ ꢄꢅ
ꢂ
the V pin. Generally, a capacitor (C ) and a resistor (R )
C
C
C
ꢁ
ꢃ ꢆ.ꢇꢂꢅ
ꢂ
in series to ground are used. Designing the compensation
network is a bit complicated and the best values depend
on the application. A practical approach is to start with
one of the circuits in this data sheet that is similar to your
application and tune the compensation network to opti-
mize the performance. LTspice® simulations can help in
this process. Stability should then be checked across all
operating conditions, including load current, input voltage
and temperature. The LT1375 data sheet contains a more
thorough discussion of loop compensation and describes
how to test the stability using a transient load.
ꢚꢛ
Cꢆ
ꢀ
C
ꢞ
ꢝ
ꢗ.ꢙꢇꢀ
R
C
ꢆꢄꢗꢘ
C
ꢚ
C
C
ꢔꢕꢖꢕ ꢚꢗꢄ
Figure 5. Model for Loop Response
Rev. C
23
For more information www.analog.com
LT8636/LT8637
APPLICATIONS INFORMATION
Output Voltage Tracking and Soft-Start
Paralleling (LT8637 Only)
T
he LT8636/LT8637 allows the user to program its output
To increase the possible output current, two LT8637s can
be connected in parallel to the same output. To do this, the
VC and FB pins are connected together, and each LT8637’s
SW node is connected to the common output through its
own inductor. The CLKOUT pin of one LT8637 should be
connected to the SYNC/MODE pin of the second LT8637
to have both devices operate in the same mode. During
FCM, spread spectrum, and synchronization modes,
both devices will operate at the same frequency. Figure 6
shows an application where two LT8637 are paralleled to
get one output capable of up to 10A.
voltage ramp rate by means of the TR/SS pin. An internal
1.9µA pulls up the TR/SS pin to INTV . Putting an exter-
nal capacitor on TR/SS enables softCsCtarting 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. For the LT8636, from
0V to 0.97V, the TR/SS voltage will override the internal
0.97V reference input to the error amplifier, thus regulat-
ing the FB pin voltage to that of TR/SS pin. When TR/
SS is above 0.97V, tracking is disabled and the feedback
voltage will regulate to the internal reference voltage.
For the LT8637, from 0V to 1.6V, the TR/SS voltage will
override the internal 0.97V reference input to the error
amplifier, thus regulating the FB pin voltage to a func-
tion of the TR/SS pin. See plot in the Typical Performance
Characteristics section. When TR/SS is above 1.6V, track-
ing 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. The TR/SS pin may
be left floating if the function is not needed.
ꢁꢊꢃꢄꢅꢍ
ꢁꢀ
ꢋ
ꢈꢉꢊ
ꢋ
C
ꢎꢏ
ꢀꢇꢌ
Cꢀ
C
ꢈꢉꢊ
Rꢀ
Rꢂ
Cꢁꢑꢈꢉꢊ
ꢆꢐ
R
C
ꢁꢊꢃꢄꢅꢍ
ꢎꢒꢓCꢔꢕꢈꢖꢗ
C
C
ꢆꢐ
ꢁꢂ
ꢋ
C
ꢎꢏ
ꢃꢄꢅꢄ ꢆꢇꢄ
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
Figure 6. Paralleling Two LT8637s
capacitor are the EN/UV pin transitioning low, V voltage
IN
falling too low, or thermal shutdown.
Rev. C
24
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LT8636/LT8637
TYPICAL APPLICATIONS
Output Power Good
There is another situation to consider in systems where
the output will be held high when the input to the LT8636/
LT8637 is absent. This may occur in battery charging
applications or in battery-backup systems where a bat-
tery or some other supply is diode ORed with the LT8636/
When the LT8636/LT8637’s output voltage is within the
8% window of the regulation point, 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 0.2% of hysteresis. PG is valid
LT8637’s output. If the V pin is allowed to float and the
IN
EN pin is held high (either by a logic signal or because it
is tied to V ), then the LT8636/LT8637’s internal circuitry
IN
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 LT8636/LT8637 can pull current from
when V is above 3.4V.
IN
The PG pin is also actively pulled low during several fault
conditions: EN/UV pin is below 1V, INTV has fallen too
CC
low, V is too low, or thermal shutdown.
IN
Shorted and Reversed Input Protection
the output through the SW pin and the V pin, which may
IN
damage the IC. Figure 7 shows a connection of the V and
The LT8636/LT8637 will tolerate a shorted output. Several
features are used for protection during output short-circuit
and brownout conditions. The first is the switching fre-
quency 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 induc-
tor current is beyond safe levels switching of the top switch
will be delayed until such time as the inductor current falls
to safe levels.
IN
EN/UV pins that will allow the LT8636/LT8637 to run only
when the input voltage is present and that protects against
a shorted or reversed input.
ꢃꢄ
ꢀ
ꢁꢂ
ꢀ
ꢁꢂ
ꢅꢆꢇꢈꢉꢈꢊ
ꢅꢆꢇꢈꢉꢋ
ꢌꢂꢊꢍꢀ
ꢐꢂꢃ
ꢇꢈꢉꢈ ꢎꢏꢋ
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, floated or tied high, the LT8636/LT8637 will stay
at the programmed frequency without foldback and only
slow switching if the inductor current exceeds safe levels.
Figure 7. Reverse VIN Protection
Rev. C
25
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LT8636/LT8637
APPLICATIONS INFORMATION
Thermal Considerations and Peak Output Current
The LT8636/LT8637’s internal power switches are capa-
ble of safely delivering up to 7A of peak output current.
However, due to thermal limits, the package can only han-
dle 7A loads for short periods of time. This time is deter-
mined by how quickly the case temperature approaches
the maximum junction rating. Figure 9 shows an example
of how case temperature rise changes with the duty cycle
of a 1kHz pulsed 7A load.
For higher ambient temperatures, care should be taken
in the layout of the PCB to ensure good heat sinking of
the LT8636/LT8637. The ground pins on the bottom of
the package should 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
LT8636/LT8637. Placing additional vias can reduce thermal
resistance further. The maximum load current should be
derated as the ambient temperature approaches the maxi-
mum junction rating. Power dissipation within the LT8636/
LT8637 can be estimated by calculating the total power
loss from an efficiency measurement and subtracting the
inductor loss. The die temperature is calculated by multiply-
ing the LT8636/LT8637 power dissipation by the thermal
resistance from junction to ambient.
ꢀꢁꢂ
ꢀCꢁꢂꢃꢄꢅ ꢀꢆꢇꢈ ꢉꢈꢅRꢀ
ꢀ
ꢀ ꢁꢂꢃ
ꢀꢁꢂ
ꢀꢁꢂ
ꢀꢁ
ꢀꢁ
ꢀꢁ
ꢀꢁ
ꢀꢁ
ꢀꢁ
ꢀ
ꢀꢁ
ꢀꢁꢂ
ꢀꢁ
ꢀ
ꢀ
ꢀ ꢁꢂ
ꢀ ꢁꢂꢃꢄ
ꢀꢁꢂꢃꢄꢅꢆ ꢇꢈꢂꢄ ꢉ ꢊ.ꢋꢌꢂ
ꢀꢁꢂꢃ ꢄꢅꢆꢇꢈꢉ ꢆꢊꢋꢉ ꢌ ꢍꢋ
The internal overtemperature protection monitors the
junction temperature of the LT8636/LT8637. If the junc-
tion temperature reaches approximately 180°C, the
LT8636/LT8637 will stop switching and indicate a fault
condition until the temperature drops about 10°C cooler.
ꢀ
ꢀ.ꢁ
ꢀ.ꢁ
ꢀ.ꢁ
ꢀ.ꢁ
ꢀ
ꢀꢁꢂꢃ CꢃCꢄꢅ ꢆꢇ ꢈꢉ ꢄꢆꢉꢀ
ꢀꢁꢂꢁ ꢃꢄꢅ
Figure 9. Case Temperature Rise vs 7A Pulsed Load
Temperature rise of the LT8636/LT8637 is worst when oper-
ating at high load, high V , and high switching frequency.
IN
The LT8636/LT8637’s top switch current limit decreases
with higher duty cycle operation for slope compensa-
tion. This also limits the peak output current the LT8636/
LT8637 can deliver for a given application. See curve in
Typical Performance Characteristics.
If the case temperature is too high for a given application,
then either V , switching frequency, or load current can be
IN
decreased to reduce the temperature to an acceptable level.
Figure 8 shows examples of how case temperature rise can
be managed by reducing VIN, switching frequency, or load.
ꢀꢁ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ ꢁꢂꢃꢄ ꢅ ꢀ ꢁꢂꢃꢄ
ꢀꢁ
ꢀꢁ
ꢀꢁ
ꢀꢁ
ꢀꢁ
ꢀ ꢁꢂꢃꢄ ꢅ ꢀ ꢁꢂꢃꢄ
ꢀꢁ
ꢀꢁ
ꢀꢁ
ꢀꢁ
ꢀꢁ
ꢀꢁ
ꢀꢁ
ꢀꢁ
ꢀ
ꢀ ꢁꢂꢃꢄ ꢅ ꢀ ꢁꢂꢃꢄ
ꢀꢁ
ꢀ ꢁꢂꢃꢄ ꢅ ꢀ ꢁꢂꢃꢄ
ꢀꢁ
ꢀꢁꢂꢃ ꢄꢃꢅRꢀ ꢆꢇ ꢈꢉꢆꢊꢊ ꢅꢆR
ꢀ ꢁ ꢂꢃꢀꢄꢅꢆꢅꢇ ꢈ.ꢉꢊꢋ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀꢁꢂꢃ CꢄRRꢅꢆꢇ ꢈꢂꢉ
ꢀꢁꢂꢁ ꢃꢄꢀ
Figure 8. Case Temperature Rise
Rev. C
26
For more information www.analog.com
LT8636/LT8637
TYPICAL APPLICATIONS
ꢀ
ꢁꢂ
ꢢ.ꢍꢀ ꢉꢈ ꢜꢠꢀ
ꢜ.ꢍꢛꢎ
ꢃꢂꢄꢅꢀ
ꢀ
ꢀ
ꢁꢂ
ꢁꢂ
ꢏꢛꢎ
ꢐꢋꢐꢌ
ꢏꢛꢎ
ꢐꢋꢐꢌ
ꢘꢂꢕ
ꢘꢂꢕ
ꢆꢉꢊꢋꢌꢋ
ꢆꢉꢊꢋꢌꢍ
Cꢆꢇꢈꢅꢉ
ꢑꢒꢉ
ꢌ.ꢌꢛꢥ
ꢐ.ꢏꢛꢎ
ꢏꢐꢐꢣ
ꢀ
ꢢꢀ
ꢢꢚ
ꢈꢅꢉ
ꢒꢓꢂCꢄꢔꢈꢕꢃ
ꢒꢙ
ꢗꢘ
ꢋ.ꢜꢦꢣ
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C
ꢏꢐꢤꢎ
ꢌꢌꢐꢝꢎ
ꢉRꢄꢒꢒ
ꢑꢁꢚꢒ
ꢜ.ꢍꢝꢎ ꢞꢆꢉꢊꢋꢌꢍꢟ
ꢏꢐꢝꢎ ꢞꢆꢉꢊꢋꢌꢋꢟ
ꢏꢛꢎ
ꢏꢔ
ꢏꢐꢐꢛꢎ
ꢏꢠꢏꢐ
ꢡꢢRꢄꢡꢍR
ꢁꢂꢉꢀ
Rꢉ
ꢎꢑ
CC
ꢜꢏ.ꢠꢣ
ꢠꢜꢌꢣ
ꢘꢂꢕ
ꢊꢋꢌꢋ ꢎꢏꢐ
ꢧ
ꢨ ꢏꢔꢥꢩ
ꢒꢙ
ꢆꢪ ꢡꢃꢆꢋꢐꢌꢐ
Figure 10. 5V, 5A Step-Down Converter with Soft-Start and Power Good
ꢀ
ꢁꢂ
ꢜꢀ ꢉꢈ ꢜꢠꢀ
ꢜ.ꢍꢛꢎ
ꢃꢂꢄꢅꢀ
ꢀ
ꢀ
ꢁꢂ
ꢁꢂ
ꢏꢛꢎ
ꢚꢋꢚꢌ
ꢏꢛꢎ
ꢚꢋꢚꢌ
ꢗꢂꢔ
ꢗꢂꢔ
ꢆꢉꢊꢋꢌꢋ
ꢆꢉꢊꢋꢌꢍ
Cꢆꢇꢈꢅꢉ
ꢐꢑꢉ
ꢠ.ꢠꢛꢥ
ꢚ.ꢏꢛꢎ
ꢏꢚꢚꢣ
ꢀ
ꢌ.ꢌꢀ
ꢢꢙ
ꢈꢅꢉ
ꢑꢒꢂCꢄꢓꢈꢔꢃ
ꢑꢘ
ꢖꢗ
ꢊ.ꢜꢢꢣ
ꢀ ꢕ
C
ꢏꢚꢤꢎ
ꢌꢌꢚꢝꢎ
ꢉRꢄꢑꢑ
ꢐꢁꢙꢑ
ꢜ.ꢍꢝꢎ ꢞꢆꢉꢊꢋꢌꢍꢟ
ꢏꢚꢝꢎ ꢞꢆꢉꢊꢋꢌꢋꢟ
ꢏꢛꢎ
ꢏꢓ
ꢏꢚꢚꢛꢎ
ꢏꢠꢏꢚ
ꢡꢢRꢄꢡꢍR
ꢁꢂꢉꢀ
Rꢉ
ꢎꢐ
CC
ꢜꢏ.ꢠꢣ
ꢜꢏꢠꢣ
ꢗꢂꢔ
ꢊꢋꢌꢋ ꢎꢏꢏ
ꢦ
ꢧ ꢏꢓꢥꢨ
ꢑꢘ
ꢆꢩ ꢡꢃꢆꢋꢚꢌꢚ
Figure 11. 3.3V, 5A Step-Down Converter with Soft-Start and Power Good
* V pin and components only apply to LT8637.
C
Rev. C
27
For more information www.analog.com
LT8636/LT8637
TYPICAL APPLICATIONS
ꢀꢁꢂ
ꢀꢁꢂꢃ
ꢀ
ꢀꢁ
ꢀ.ꢁꢂ ꢃꢄ ꢅꢆꢂ
ꢀꢁꢂꢃ
ꢀꢁꢀꢂ
ꢀꢁꢂꢃ
ꢀꢁꢀꢂ
ꢀꢁꢂꢃ
ꢀꢁꢀꢂ
ꢀꢁꢂꢃꢄ
ꢀ
ꢀ
ꢀꢁ
ꢀꢁ
ꢀꢁꢂ
ꢀꢁꢀꢂ
ꢀꢁꢂ
ꢀꢁꢀꢂ
ꢀꢁꢂ
ꢀꢁꢂ
ꢀꢁꢂꢃ ꢂꢄꢅ ꢆꢃꢇꢈ ꢁꢂ
ꢅꢉꢁꢃ CꢁRCꢆꢁꢅꢊ
ꢀꢁꢂꢃꢄꢃ
ꢀꢁꢂꢃꢄꢅ
ꢀꢁꢂ
ꢀ.ꢁꢂꢃ
Cꢀꢁꢂꢃꢄꢅ ꢆꢇꢅ ꢄRꢈꢉꢉ
ꢀꢁꢂ
ꢀ.ꢁꢂꢃ
ꢀ
ꢀꢁꢂ
ꢀꢁꢂꢃ
ꢀꢁ
ꢀꢁ
CC
ꢀꢁ
ꢀꢁꢂCꢃꢄꢅꢆꢇ
ꢀꢁꢂꢃ
ꢀ.ꢁꢂꢃ
ꢀ.ꢁꢂꢃ ꢄꢅꢆꢇꢈꢉꢁꢊ
ꢋꢌꢂꢃ ꢄꢅꢆꢇꢈꢉꢈꢊ
ꢀꢁ
ꢀ ꢁ
C
ꢀꢁꢁꢂꢃ
ꢀꢁꢀꢂ
ꢀꢁRꢂꢀꢃR
Rꢀ
ꢀꢁ
ꢀꢀꢁꢂꢃ
ꢀꢁꢂ
ꢀꢁ.ꢂꢃ
ꢀꢁꢂꢃ
ꢀ
ꢀ ꢁꢂꢃꢄ
ꢀꢁ
L: XEL6030
FB1 BEAD: WE-MPSB 100Ω 8A 1812
ꢀꢁꢂꢁ ꢃꢄꢅ
Figure 12. Ultralow EMI 5V, 5A Step-Down Converter with Spread Spectrum
ꢀ
ꢁꢂ
ꢠ.ꢋꢀ ꢇꢒ ꢚꢞꢀ
ꢚ.ꢋꢙꢌ
ꢃꢂꢄꢅꢀ
ꢀ
ꢀ
ꢁꢂ
ꢁꢂ
ꢍꢙꢌ
ꢍꢙꢌ
ꢘꢉꢘꢊ
ꢘꢉꢘꢊ
ꢗꢂꢓ
ꢗꢂꢓ
ꢆꢇꢈꢉꢊꢉ
ꢆꢇꢈꢉꢊꢋ
ꢎꢏꢇ
ꢏꢕ
ꢈ.ꢚꢠꢡ
ꢍ.ꢠꢙꢢ
ꢘ.ꢍꢙꢌ
ꢀ
ꢒꢅꢇ
ꢀ ꢔ
C
ꢀꢁꢂꢃ ꢂꢄꢅ ꢆꢃꢇꢈ ꢁꢂ
ꢅꢉꢁꢃ CꢁRCꢆꢁꢅꢊ
ꢠꢀ
ꢠꢖ
ꢏꢐꢂCꢄꢑꢒꢓꢃ
ꢊꢊꢘꢛꢌ
Cꢀꢁꢂꢃꢄꢅ ꢆꢇꢅ ꢄRꢈꢉꢉ
ꢎꢁꢖꢏ
ꢚ.ꢋꢛꢌ ꢜꢆꢇꢈꢉꢊꢋꢝ
ꢍꢘꢛꢌ ꢜꢆꢇꢈꢉꢊꢉꢝ
ꢍꢙꢌ
ꢍꢑ
ꢍꢘꢘꢙꢌ
ꢍꢞꢍꢘ
ꢟꢠRꢄꢟꢋR
ꢁꢂꢇꢀ
Rꢇ
ꢌꢎ
CC
ꢍꢋ.ꢈꢡ
ꢞꢚꢊꢡ
ꢗꢂꢓ
ꢈꢉꢊꢉ ꢌꢍꢊ
ꢣ
ꢤ ꢞꢑꢢꢥ
ꢏꢕ
ꢆꢦ ꢟꢃꢆꢉꢘꢊꢘ
Figure 13. 2MHz 5V, 5A Step-Down Converter with Spread Spectrum
* V pin and components only apply to LT8637.
C
Rev. C
28
For more information www.analog.com
LT8636/LT8637
TYPICAL APPLICATIONS
ꢀ
ꢁꢂ
ꢎꢀ ꢇꢓ ꢎꢞꢀ
ꢎ.ꢋꢚꢌ
ꢃꢂꢄꢅꢀ
ꢀ
ꢀ
ꢁꢂ
ꢁꢂ
ꢍꢚꢌ
ꢍꢚꢌ
ꢙꢉꢙꢊ
ꢙꢉꢙꢊ
ꢘꢂꢔ
ꢘꢂꢔ
ꢆꢇꢈꢉꢊꢉ
ꢆꢇꢈꢉꢊꢋ
ꢏꢐꢇ
ꢐꢖ
ꢍꢉ.ꢞꢡ
ꢍꢚꢢ
ꢙ.ꢍꢚꢌ
ꢀ
ꢊ.ꢊꢀ
ꢠꢗ
ꢓꢅꢇ
ꢀ ꢕ
C
ꢀꢁꢂꢃ ꢂꢄꢅ ꢆꢃꢇꢈ ꢁꢂ
ꢅꢉꢁꢃ CꢁRCꢆꢁꢅꢊ
ꢐꢑꢂCꢄꢒꢓꢔꢃ
ꢞꢞꢙꢛꢌ
ꢏꢁꢗꢐ
Cꢀꢁꢂꢃꢄꢅ ꢆꢇꢅ ꢄRꢈꢉꢉ
ꢎ.ꢋꢛꢌ ꢜꢆꢇꢈꢉꢊꢋꢝ
ꢍꢙꢛꢌ ꢜꢆꢇꢈꢉꢊꢉꢝ
ꢍꢚꢌ
ꢍꢒ
ꢍꢙꢙꢚꢌ
ꢍꢞꢍꢙ
ꢟꢠRꢄꢟꢋR
ꢁꢂꢇꢀ
Rꢇ
ꢌꢏ
CC
ꢍꢋ.ꢈꢡ
ꢎꢍꢞꢡ
ꢘꢂꢔ
ꢈꢉꢊꢉ ꢌꢍꢎ
ꢣ
ꢤ ꢞꢒꢢꢥ
ꢐꢖ
ꢆꢦ ꢟꢃꢆꢉꢙꢊꢙ
Figure 14. 2MHz 3.3V, 5A Step-Down Converter with Spread Spectrum
ꢀ
ꢁꢂ
ꢄꢃ.ꢠꢀ ꢉꢒ ꢟꢃꢀ
ꢟ.ꢠꢞꢍ
ꢄꢞꢍ
ꢝꢋꢝꢌ
ꢅꢂꢆꢇꢀ
ꢀ
ꢀ
ꢁꢂꢃ
ꢁꢂꢄ
ꢄꢞꢍ
ꢝꢋꢝꢌ
ꢘꢂꢓꢄ
ꢘꢂꢓꢃ
ꢏꢐꢉ
ꢈꢉꢊꢋꢌꢋ
ꢟ.ꢠꢞꢔ
ꢝ.ꢄꢞꢍ
ꢟ.ꢠꢡꢍ
ꢀ
ꢄꢃꢀ
ꢎꢜ
ꢒꢇꢉ
ꢐꢛ
ꢄꢝꢣꢍ
ꢏꢁꢜꢐ
ꢉRꢆꢐꢐ
ꢄꢞꢍ
ꢄꢚ
ꢟꢠꢞꢍ
ꢄꢃꢄꢝ
ꢁꢂꢉꢀ
Rꢉ
ꢍꢏ
CC
ꢟꢄ.ꢃꢤ
ꢢꢎRꢆꢢꢠR
ꢊꢊ.ꢠꢤ
ꢘꢂꢓ
ꢊꢋꢌꢋ ꢍꢄꢎ
ꢥ
ꢦ ꢄꢚꢔꢧ
ꢐꢛ
ꢈꢕ ꢢꢅꢈꢋꢝꢋꢝ
ꢑꢁꢂꢐ ꢂꢒꢉ ꢇꢐꢅꢓ ꢁꢂ ꢉꢔꢁꢐ CꢁRCꢇꢁꢉꢕ
Cꢈꢖꢒꢇꢉꢗ ꢑꢘꢗ ꢐꢙꢂCꢆꢚꢒꢓꢅ
Figure 15. 12V, 5A Step-Down Converter
* V pin and components only apply to LT8637.
C
Rev. C
29
For more information www.analog.com
LT8636/LT8637
PACKAGE DESCRIPTION
ꢛ
ꢜ
ꢞ
ꢡ ꢄ ꢄ ꢄ
ꢪ ꢪ ꢪ
ꢞ
ꢞ
× ꢑ ꢋ
ꢞ
ꢥ ꢥ ꢟ ꢟ ꢟ
ꢞ
ꢋ . ꢧ ꢌ ꢋ ꢋ
ꢋ . ꢑ ꢌ ꢋ ꢋ
ꢋ . ꢋ ꢋ ꢋ ꢋ
ꢋ . ꢑ ꢌ ꢋ ꢋ
ꢋ . ꢧ ꢌ ꢋ ꢋ
ꢝ ꢝ ꢝ
ꢞ
× ꢑ
Rev. C
30
For more information www.analog.com
LT8636/LT8637
REVISION HISTORY
REV
DATE
DESCRIPTION
PAGE NUMBER
A
11/19 Replaced 5A with 5/7A Peak in Title
Replaced 7A Peak Output with 7A Peak Transient Output
Replace Tracking with Power Good
1
1
1
Added AEC-Q100 Quaified for Automotive Applications
Clarified GND pin numbers in Pin Functions
Clarified Equations 7, 8, 9
1
10
16-17
2
B
C
04/20 Added LT8636JV#WTRPBF to the Order Information Table
12/20 Added LT8637
Added 8636MP
All
2, 4
Rev. C
Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog
Devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use. Specifications
subject to change without notice. No license isgrantedbyimplicationor otherwiseunderany patent or patent rights of Analog Devices.
31
LT8636/LT8637
TYPICAL APPLICATIONS
2MHz 1.8V, 5A Step-Down Converter
ꢀ
ꢁꢂ
ꢌ.ꢥꢀ ꢉꢒ ꢃꢃꢀ
ꢦꢥꢃꢀ ꢉRꢍꢂꢐꢁꢅꢂꢉꢧ
ꢥ.ꢢꢝꢜ
ꢅꢂꢆꢇꢀ
ꢀ
ꢀ
ꢁꢂꢃ
ꢁꢂꢄ
ꢄꢝꢜ
ꢎꢋꢎꢌ
ꢄꢝꢜ
ꢎꢋꢎꢌ
ꢘꢂꢓꢄ
ꢘꢂꢓꢃ
ꢏꢐꢉ
ꢄꢝꢔ
ꢎ.ꢄꢝꢜ
ꢄꢝꢜ
ꢀ
ꢄ.ꢊꢀ
ꢡꢍ
ꢈꢉꢊꢋꢌꢋ
ꢒꢇꢉ
ꢐꢛ
ꢄꢎꢣꢜ
ꢅꢟꢉꢅRꢂꢍꢈ
ꢐꢒꢇRCꢅ ꢠꢌ.ꢄꢀ
ꢒR ꢘꢂꢓ
ꢏꢁꢍꢐ
ꢉRꢆꢐꢐ
ꢄꢎꢞꢜ
ꢊꢋꢋꢤ
ꢄꢚ
ꢄꢝꢜ
ꢄꢎꢎꢝꢜ
ꢄꢃꢄꢎ
ꢟꢡRꢆꢟꢢR
ꢁꢂꢉꢀ
Rꢉ
ꢜꢏ
CC
ꢄꢢ.ꢊꢤ
ꢘꢂꢓ
ꢊꢋꢌꢋ ꢉꢍꢎꢃ
ꢨ
ꢩ ꢃꢚꢔꢪ
ꢐꢛ
ꢈꢕ ꢟꢅꢈꢋꢎꢌꢎ
ꢑꢁꢂꢐ ꢂꢒꢉ ꢇꢐꢅꢓ ꢁꢂ ꢉꢔꢁꢐ CꢁRCꢇꢁꢉꢕ
Cꢈꢖꢒꢇꢉꢗ ꢑꢘꢗ ꢐꢙꢂCꢆꢚꢒꢓꢅ
RELATED PARTS
PART
DESCRIPTION
COMMENTS
= 3.4V, V
LT8640S/
LT8643S
42V, 6A Synchronous Step-Down Silent Switcher 2 with I = 2.5μA
V
I
= 42V, V
= 0.97V, I = 2.5µA,
Q
Q
IN(MIN)
IN(MAX)
OUT(MIN)
OUT(MIN)
OUT(MIN)
< 1µA, 4mm × 4mm LQFN-24
SD
LT8640/
LT8640-1
42V, 5A, 96% Efficiency, 3MHz Synchronous MicroPower Step-Down
V
SD
= 3.4V, V
= 42V, V
= 0.97V, I = 2.5µA,
Q
IN(MIN)
IN(MAX)
DC/DC Converter with I = 2.5μA
I
< 1µA, 3mm × 4mm QFN-18
Q
LT8645S/
LT8646S
65V, 8A, Synchronous Step-Down Silent Switcher 2 with I = 2.5μA
V
SD
= 3.4V, V
= 65V, V
= 0.97V, I = 2.5µA,
Q
Q
IN(MIN)
IN(MAX)
I
< 1µA, 4mm × 6mm LQFN-32
LT8641
65V, 3.5A, 95% Efficiency, 3MHz Synchronous MicroPower Step-Down
V
SD
= 3V, V
= 65V, V
= 0.81V, I = 2.5µA,
Q
IN(MIN)
IN(MAX)
OUT(MIN)
DC/DC Converter with I = 2.5μA
I
< 1µA, 3mm × 4mm QFN-18
Q
LT8609/
LT8609A
42V, 2A, 94% Efficiency, 2.2MHz Synchronous MicroPower Step-Down
V
SD
= 3V, V
= 42V, V
= 0.8V, I = 2.5µA,
Q
IN(MIN)
IN(MAX)
OUT(MIN)
DC/DC Converter with I = 2.5µA
I
< 1µA, MSOP-10E
Q
LT8610A/
LT8610AB
42V, 3.5A, 96% Efficiency, 2.2MHz Synchronous MicroPower Step-
V
SD
= 3.4V, V
= 42V, V = 0.97V, I = 2.5µA,
OUT(MIN) Q
IN(MIN)
IN(MAX)
Down DC/DC Converter with I = 2.5µA
I
< 1µA, MSOP-16E
Q
LT8610AC
LT8610
LT8616
LT8620
LT8614
LT8612
LT8602
42V, 3.5A, 96% Efficiency, 2.2MHz Synchronous MicroPower Step-
V
SD
= 3V, V
= 42V, V
= 0.8V, I = 2.5µA,
IN(MIN)
IN(MAX)
OUT(MIN) Q
Down DC/DC Converter with I = 2.5µA
I
< 1µA, MSOP-16E
Q
42V, 2.5A, 96% Efficiency, 2.2MHz Synchronous MicroPower Step-
V
= 3.4V, V
< 1µA, MSOP-16E
= 42V, V
= 0.97V, I = 2.5µA,
Q
IN(MIN)
IN(MAX)
OUT(MIN)
OUT(MIN)
Down DC/DC Converter with I = 2.5µA
I
SD
Q
42V, Dual 2.5A + 1.5A, 95% Efficiency, 2.2MHz Synchronous
V
= 3.4V, V
= 42V, V
= 0.8V, I = 5µA,
Q
IN(MIN)
IN(MAX)
MicroPower Step-Down DC/DC Converter with I = 5µA
I
SD
< 1µA, TSSOP-28E, 3mm × 6mm QFN-28
Q
65V, 2.5A, 94% Efficiency, 2.2MHz Synchronous MicroPower Step-
V
= 3.4V, V
= 65V, V
= 0.97V, I = 2.5µA,
OUT(MIN) Q
IN(MIN)
IN(MAX)
Down DC/DC Converter with I = 2.5µA
I
SD
< 1µA, MSOP-16E, 3mm × 5mm QFN-24
Q
42V, 4A, 96% Efficiency, 2.2MHz Synchronous Silent Switcher Step-
V
= 3.4V, V
< 1µA, 3mm × 4mm QFN18
= 42V, V
= 0.97V, I = 2.5µA,
Q
IN(MIN)
IN(MAX)
OUT(MIN)
Down DC/DC Converter with I = 2.5µA
I
SD
Q
42V, 6A, 96% Efficiency, 2.2MHz Synchronous MicroPower Step-Down
V
= 3.4V, V
< 1µA, 3mm × 6mm QFN-28
= 42V, V
= 0.97V, I = 3.0µA,
Q
IN(MIN)
IN(MAX)
OUT(MIN)
DC/DC Converter with I = 2.5µA
I
SD
Q
42V, Quad Output (2.5A + 1.5A + 1.5A + 1.5A) 95% Efficiency, 2.2MHz
V
= 3V, V
< 1µA, 6mm × 6mm QFN-40
= 42V, V
= 0.8V, I = 2.5µA,
OUT(MIN) Q
IN(MIN)
IN(MAX)
Synchronous MicroPower Step-Down DC/DC Converter with I = 25µA
I
SD
Q
Rev. C
12/20
www.analog.com
32
ANALOG DEVICES, INC. 2020
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SI9137LG
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SI9122E
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