LT8636/LT8637
42V, 5A/7A Peak Synchronous Step-Down
Silent Switcher with 2.5µA Quiescent Current
FEATURES
DESCRIPTION
Silent Switcher ® Architecture
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
IN
OUT
n Up to 95% Efficiency at 2MHz, 12V to 5V
IN
OUT
n Wide Input Voltage Range: 3.4V to 42V
n 5A Maximum Continuous, 7A Peak Transient Output
n Ultralow Quiescent Current Burst Mode® Operation
n 2.5µA I Regulating 12V to 3.3V
Q
IN
OUT (LT8636)
n Output Ripple < 10mV
P-P
n External Compensation: Fast Transient Response
and Current Sharing (LT8637)
n Fast Minimum Switch On-Time: 30ns
n Low Dropout Under All Conditions: 100mV at 1A
n Forced Continuous Mode
n Adjustable and Synchronizable: 200kHz to 3MHz
n Output Soft-Start and Power Good
n Small 20-Lead 4mm × 3mm LQFN Package
n AEC-Q100 Qualified for Automotive Applications
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.
APPLICATIONS
All registered trademarks and trademarks are the property of their respective owners. Protected
by U.S. patents, including 8823345.
n
n
n
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.
Burst Mode operation enables ultralow standby current
consumption, forced continuous mode can control frequency harmonics across the entire output load range, or
spread spectrum operation can further reduce EMI emissions. 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.
Automotive and Industrial Supplies
General Purpose Step-Down
TYPICAL APPLICATION
5V, 5A Step-Down Converter
12VIN to 5VOUT Efficiency
VIN
5.7V TO 42V
1µF
EN/UV
VIN
1µF
BST
0.1µF
SW
3.3µH
VOUT
5V
5A
BIAS
1µF
41.2k
fSW = 1MHz
INTVCC
10pF
RT
2.8
EFFICIENCY
100µF
243k
2.0
80
1.6
1.2
75
POWER LOSS
65
60
0.5
8636 TA01a
2.4
85
70
1M
FB
GND
95
90
GND
LT8636
3.2
1
POWER LOSS (W)
GND
VIN
EFFICIENCY (%)
4.7µF
100
0.8
1MHz, L = 2.7µH
2MHz, L = 1.5µH 0.4
3MHz, L = 1µH
0
1.5 2 2.5 3 3.5 4 4.5 5
LOAD CURRENT (A)
8636 TA01b
Rev. C
Document Feedback
For more information www.analog.com
1
LT8636/LT8637
ABSOLUTE MAXIMUM RATINGS
(Note 1)
VIN, EN/UV, PG...........................................................42V
BIAS...........................................................................25V
FB, TR/SS ...................................................................4V
SYNC/MODE Voltage ..................................................6V
Operating Junction Temperature Range (Note 2)
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
PIN CONFIGURATION
LT8636
LT8637
FB
TR/SS
RT
FB
VC
TR/SS
RT
TOP VIEW
FB
TOP VIEW
20
19
18
17
20
19
18
17
2
15 SYNC/MODE
INTVCC
3
GND
4
14 EN/UV
21
GND
1
16 CLKOUT
BIAS
2
15 SYNC/MODE
INTVCC
3
GND
4
5
12 NC
6
11 VIN
13 GND
6
11 VIN
VIN
7
8
9
10
SW
VIN
SW
12 NC
SW
5
BST
NC
NC
14 EN/UV
21
GND
7
8
13 GND
9
10
SW
BIAS
PG
SW
16 CLKOUT
SW
1
BST
PG
LQFN PACKAGE
20-LEAD (4mm × 3mm × 0.94mm)
LQFN PACKAGE
20-LEAD (4mm × 3mm × 0.94mm)
JEDEC BOARD: θJA = 41°C/W, θJC(top) = 50.6°C/W,
θJC(pad) = 8.0°C/W, (NOTE 3)
DEMO BOARD: θJA = 26°C/W, ΨJT = 0.8°C/W
EXPOSED PAD (PIN 21) IS GND, SHOULD BE SOLDERED TO PCB
JEDEC BOARD: θJA = 41°C/W, θJC(top) = 50.6°C/W,
θJC(pad) = 8.0°C/W, (NOTE 3)
DEMO BOARD: θJA = 26°C/W, ΨJT = 0.8°C/W
EXPOSED PAD (PIN 21) IS GND, SHOULD BE SOLDERED TO PCB
ORDER INFORMATION
PART NUMBER
PART MARKING*
FINISH CODE
PAD FINISH
PACKAGE
TYPE**
MSL
RATING
LT8636EV#PBF
LT8636JV#PBF
LT8636HV#PBF
–40°C to 125°C
LT8637JV#PBF
–40°C to 150°C
8636
e4
LT8636MPV#PBF
LT8637EV#PBF
TEMPERATURE RANGE
Au (RoHS)
LQFN (Laminate Package
with QFN Footprint)
3
–40°C to 150°C
–55°C to 150°C
–40°C to 125°C
8637
–40°C to 150°C
Rev. C
2
For more information www.analog.com
LT8636/LT8637
ORDER INFORMATION
PART NUMBER
PART MARKING*
FINISH CODE
PACKAGE
TYPE**
PAD FINISH
MSL
RATING
TEMPERATURE RANGE
AUTOMOTIVE PRODUCTS***
LT8636EV#WPBF
LT8636JV#WPBF
LT8636JV#WTRPBF
–40°C to 125°C
e4
LT8636HV#WPBF
LT8637EV#WPBF
LT8637JV#WPBF
–40°C to 150°C
8636
Au (RoHS)
LQFN (Laminate Package
with QFN Footprint)
–40°C to 150°C
3
–40°C to 150°C
–40°C to 125°C
8637
–40°C to 150°C
• Contact the factory for parts specified with wider operating temperature
ranges. *Device temperature grade is identified by a label on the
shipping container.
• Pad finish code is per IPC/JEDEC J-STD-609.
• Recommended PCB Assembly and Manufacturing Procedures
• Package and Tray Drawings
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.
The
l denotes the specifications which apply over the full operating
ELECTRICAL
CHARACTERISTICS
temperature range, otherwise specifications are at TA = 25°C.
PARAMETER
CONDITIONS
Minimum Input Voltage
VIN Quiescent Current in Shutdown
TYP
MAX
l
MIN
3.0
3.4
V
l
1
1
3
10
µA
µA
l
1.7
1.7
4
10
µA
µA
l
230
230
290
340
µA
µA
19
25
µA
VEN/UV = 0V
LT8636 VIN Quiescent Current in Sleep
(Internal Compensation)
VEN/UV = 2V, VFB > 0.97V, VSYNC = 0V
LT8637 VIN Quiescent Current in Sleep
(External Compensation)
VEN/UV = 2V, VFB > 0.97V, VSYNC = 0V, VBIAS = 0V
VEN/UV = 2V, VFB > 0.97V, VSYNC = 0V, VBIAS = 5V
UNITS
LT8637 BIAS Quiescent Current in Sleep
VEN/UV = 2V, VFB > 0.97V, VSYNC = 0V, VBIAS = 5V
200
260
µA
LT8636 VIN Current in Regulation
VOUT = 0.97V, VIN = 6V, ILOAD = 1mA, VSYNC = 0
220
390
µA
Feedback Reference Voltage
VIN = 6V
VIN = 6V
l
0.970
0.970
0.974
0.982
V
V
VIN = 4.0V to 36V
l
0.004
0.02
%/V
Feedback Voltage Line Regulation
Feedback Pin Input Current
VFB = 1V
LT8637 Error Amp Transconductance
VC = 1.25V
0.966
0.956
–20
20
1.7
LT8637 Error Amp Gain
nA
mS
260
LT8637 VC Source Current
VFB = 0.77V, VC = 1.25V
350
µA
LT8637 VC Sink Current
VFB = 1.17V, VC = 1.25V
350
µA
5
A/V
LT8637 VC Pin to Switch Current Gain
LT8637 VC Clamp Voltage
BIAS Pin Current Consumption
VBIAS = 3.3V, fSW = 2MHz
2.6
V
14
mA
Rev. C
For more information www.analog.com
3
LT8636/LT8637
The
l denotes the specifications which apply over the full operating
ELECTRICAL
CHARACTERISTICS
temperature range, otherwise specifications are at TA = 25°C.
PARAMETER
CONDITIONS
Minimum On-Time
ILOAD = 1.5A, SYNC = 0V
ILOAD = 1.5A, SYNC = 2V
MIN
l
l
Minimum Off-Time
Oscillator Frequency
RT = 221k
RT = 60.4k
RT = 18.2k
Top Power NMOS On-Resistance
ISW = 1A
l
l
l
180
665
1.8
TYP
MAX
30
30
50
45
ns
ns
80
110
ns
210
700
1.95
240
735
2.1
kHz
kHz
MHz
66
Top Power NMOS Current Limit
l
Bottom Power NMOS On-Resistance
VINTVCC = 3.4V, ISW = 1A
SW Leakage Current
VIN = 42V, VSW = 0V, 42V
EN/UV Pin Threshold
EN/UV Rising
7.5
10
mΩ
12.5
27
–3
l
0.94
EN/UV Pin Hysteresis
1.06
40
–20
A
mΩ
3
1.0
UNITS
µA
V
mV
EN/UV Pin Current
VEN/UV = 2V
PG Upper Threshold Offset from VFB
VFB Falling
l
5
7.5
10.25
%
PG Lower Threshold Offset from VFB
VFB Rising
l
–10.75
–8
–5.25
%
PG Hysteresis
20
0.2
PG Leakage
VPG = 3.3V
PG Pull-Down Resistance
VPG = 0.1V
l
–80
SYNC/MODE Threshold
SYNC/MODE DC and Clock Low Level Voltage
SYNC/MODE Clock High Level Voltage
SYNC/MODE DC High Level Voltage
l
l
l
Spread Spectrum Modulation
Frequency Range
RT = 60.4k, VSYNC = 3.3V
Spread Spectrum Modulation Frequency
VSYNC = 3.3V
Fault Condition, TR/SS = 0.1V
VIN Rising
1.2
nA
2000
Ω
0.9
1.2
2.55
1.4
2.9
V
V
V
%
1.9
kHz
2.6
200
35
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 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
80
700
3
l
TR/SS Pull-Down Resistance
2.2
%
22
TR/SS Source Current
VIN to Disable Forced Continuous Mode
0.7
nA
37
µA
Ω
39
V
lifetime is derated at junction temperatures greater than 125°C. The junction
temperature (TJ, in °C) is calculated from the ambient temperature (TA in
°C) and power dissipation (PD, in Watts) according to the formula:
TJ = TA + (PD • θJA)
where θJA (in °C/W) is the package thermal impedance.
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 3.3VOUT Efficiency
vs Frequency
3.2
2.8
95
EFFICIENCY
2.4
1.6
1.2
75
POWER LOSS
60
0.5
1
L = XEL6060 0.8
85
2.0
80
1.6
1.2
75
POWER LOSS
65
60
0.5
1
100
L = XEL6060, 2.2µH
95
EFFICIENCY (%)
2.1
80
1.8
75
1.5
70
1.2
POWER LOSS
65
fSW = 1MHz
60
55
0
1
2
3
LOAD CURRENT (A)
0.9
POWER LOSS (W)
EFFICIENCY
85
EFFICIENCY (%)
2.4
90
50
100
2.7
0.6
60
Burst Mode OPERATION
fSW = 1MHz
L = XEL6060, 4.7µH
50
100
VIN = 12V
VIN = 24V
VIN = 36V
30
0.1
1
10
100
LOAD CURRENT (mA)
1000
EFFICIENCY (%)
EFFICIENCY (%)
100
1
2
3
LOAD CURRENT (A)
VIN = 12V
VIN = 24V
VIN = 36V
0.1
1
10
100
LOAD CURRENT (mA)
70
60
50
40
VIN = 12V
VIN = 24V
VIN = 36V
20
10
0.1
1000
fSW = 1MHz
L = IHLP3232DZ–01, 4.7µH
1
10
100
LOAD CURRENT (mA)
1000
8636 G06
LT8637 Low Load Efficiency at
3.3VOUT
Efficiency vs Frequency
96
94
92
70
60
50
40
VIN = 12V
VIN = 24V
VIN = 36V
30
fSW = 1MHz
L = IHLP3232DZ–01, 4.7µH
20
10
0.1
0.6
VIN = 12V
VIN = 24V 0.3
VIN = 36V
0
4
5
LT8637 Low Load Efficiency at
5VOUT
30
80
40
0
0.9
8636 G03
8636 G05
80
20
0.01
50
90
50
fSW = 1MHz
55
80
20
0.01
90
Burst Mode OPERATION
fSW = 1MHz
L = XEL6060, 4.7µH
1.2
POWER LOSS
65
80
30
LT8636 Low Load Efficiency at
3.3VOUT
60
1.5
70
90
40
VIN = 12V
VIN = 24V 0.3
VIN = 36V
0
4
5
70
1.8
90
8636 G04
100
2.1
75
60
LT8636 Low Load Efficiency at
5VOUT
70
2.7
80
8636 G02
3.0
3.0
2.4
EFFICIENCY
85
L = XEL6060 0.8
1MHz, L = 2.2µH
0.4
2MHz, L = 1µH
3MHz, L = 1µH
0
1.5 2 2.5 3 3.5 4 4.5 5
LOAD CURRENT (A)
8636 G01
Efficiency at 3.3VOUT
L = XEL6060, 2.7µH
90
2.4
EFFICIENCY
70
1MHz, L = 2.7µH
2MHz, L = 1.5µH 0.4
3MHz, L = 1µH
0
1.5 2 2.5 3 3.5 4 4.5 5
LOAD CURRENT (A)
2.8
95
1
10
100
LOAD CURRENT (mA)
1000
8636 G07
8636 G08
EFFICIENCY (%)
65
EFFICIENCY (%)
80
100
POWER LOSS (W)
2.0
90
3.2
POWER LOSS (W)
85
70
95
POWER LOSS (W)
EFFICIENCY (%)
90
Efficiency at 5VOUT
100
EFFICIENCY (%)
100
EFFICIENCY (%)
12VIN to 5VOUT Efficiency
vs Frequency
90
88
86
84 V = 12V
IN
VOUT = 3.3V
82 I
LOAD = 2A
L = IHLP3232DZ-01, 4.7µH
80
0
0.5
1
1.5
2
2.5
SWITCHING FREQUENCY (MHz)
3
8636 G09
Rev. C
For more information www.analog.com
5
LT8636/LT8637
TYPICAL PERFORMANCE CHARACTERISTICS
Burst Mode Operation Efficiency
vs Inductor Value (LT8636)
Reference Voltage
REFERENCE VOLTAGE (mV)
VIN = 12V
95
EFFICIENCY (%)
90
VIN = 24V
85
80
75
VOUT = 5V
ILOAD = 10mA
L = IHLP3232DZ-01
70
65
1
2
3
4
5
6
INDUCTOR VALUE (µH)
1.03
977
1.02
975
1.01
973
971
969
967
961
–50 –25
8
LT8636 Load Regulation
0
0.05
VOUT = 5V
VIN = 12V
VSYNC = 0V
2
3
4
LOAD CURRENT (A)
5
0.10
0.08
0.20
0.10
0.00
–0.10
–0.20
–0.40
0
1
LT8637 Line Regulation
0.00
–0.02
5
6
–0.08
LT8636 No-Load Supply Current
0
–0.03
–0.06
–0.09
VOUT = 5V
ILOAD = 1A
–0.12
5
10
15
20 25 30 35
INPUT VOLTAGE (V)
40
45
8636 G16
10
15
20 25 30 35
INPUT VOLTAGE (V)
45
VOUT = 5V
L = 4.7µH
IN REGULATION
200
3.0
2.5
2.0
VOUT = 3.3V
L = 4.7µH
BIAS = VOUT
IN REGULATION
1.5
1.0
40
LT8637 No-Load Supply Current
INPUT CURRENT (µA)
INPUT CURRENT (µA)
0.09
0.03
5
225
3.5
0.06
VOUT = 5V
ILOAD = 1A
8636 G15
4.0
0.12
CHANGE IN VOUT (%)
0.02
8636 G14
0.15
–0.15
0.04
–0.06
2
3
4
LOAD CURRENT (A)
8636 G13
0.06
–0.04
VOUT = 5V
VIN = 12V
VSYNC = 0V
–0.30
6
25 50 75 100 125 150
TEMPERATURE (°C)
LT8636 Line Regulation
CHANGE IN VOUT (%)
CHANGE IN VOUT (%)
CHANGE IN VOUT (%)
0
0
0.12
0.30
0.05
EN FALLING
8636 G12
LT8637 Load Regulation
0.10
1
0.98
0.95
–50 –25
25 50 75 100 125 150
TEMPERATURE (°C)
0.40
0
0.99
8636 G11
0.15
–0.10
1.00
0.96
963
7
EN RISING
0.97
965
8636 G10
–0.15
EN Pin Thresholds
979
EN THRESHOLD (V)
100
0
5
10
15 20 25 30 35
INPUT VOLTAGE (V)
40
45
8636 G17
175
150
125
100
75
50
25
5
10
15
20 25 30 35
INPUT VOLTAGE (V)
40
45
8636 G18
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
11.0
Switch Drop vs Temperature
150
12
SWITCH CURRENT = 1A
10.5
125
9.0
8.5
8.0
7.5
10
SWITCH DROP (mV)
11
9.5
CURRENT LIMIT (A)
CURRENT LIMIT (A)
10.0
5% DC
9
7.0
100
TOP SWITCH
75
50
25
BOTTOM SWITCH
6.5
6.0
0.1
0.3
0.5
DUTY CYCLE
0.7
8
–50 –25
0.9
0
8636 G19
600
DROPOUT VOLTAGE (mV)
SWITCH DROP (mV)
300
TOP SWITCH
200
150
100
0
400
300
200
BOTTOM SWITCH
0
1
2
3
4
SWITCH CURRENT (A)
0
5
0
0.5
1
1.5 2 2.5 3 3.5
LOAD CURRENT (A)
4
4.5
Switching Frequency
720
710
700
690
680
670
0
20
–50
5
25 50 75 100 125 150
TEMPERATURE (°C)
8636 G25
ILOAD = 2A
VOUT = 0.97V
fSW = 3MHz
–25
0
25
50
75
TEMPERATURE (°C)
1.2
1000
1.0
800
0.8
600
400
0
FRONT PAGE APPLICATION
VIN = 12V
VOUT = 5V
0
100
200
300
400
LOAD CURRENT (mA)
125
LT8636 Soft-Start Tracking
1200
200
100
8636 G24
FB VOLTAGE (V)
RT = 60.4k
660
–50 –25
28
Burst Frequency
SWITCHING FREQUENCY (kHz)
SWITCHING FREQUENCY (kHz)
730
32
8636 G23
8636 G22
740
36
24
100
50
125
Burst Mode OPERATION
FORCED CONTINUOUS MODE
40
MINIMUM ON–TIME (ns)
500
100
Minimum On-Time
44
VIN = 5V
VOUT SET TO REGULATE AT 5V
L = IHLP3232DZ-01, 1µH
450
350
0
25
50
75
TEMPERATURE (°C)
8636 G21
Dropout Voltage
Switch Drop vs Switch Current
400
–25
8636 G20
500
250
0
–50
25 50 75 100 125 150
TEMPERATURE (°C)
500
600
8636 G26
0.6
0.4
0.2
0
0
0.2
1.0
0.4 0.6 0.8
TR/SS VOLTAGE (V)
1.2
1.4
8636 G27
Rev. C
For more information www.analog.com
7
LT8636/LT8637
TYPICAL PERFORMANCE CHARACTERISTICS
LT8637 Soft-Start Tracking
2.2
0.6
0.4
0.2
0.2
0.4
0.6 0.8 1 1.2
TR/SS VOLTAGE (V)
1.4
1.6
2.0
1.9
1.8
1.7
1.6
PG THRESHOLD OFFSET FROM VREF (%)
PG THRESHOLD OFFSET FROM VREF (%)
–250
–500
–200
0
25 50 75 100 125 150
TEMPERATURE (°C)
9.0
8.5
FB RISING
7.5
FB FALLING
6.5
25 50 75 100 125 150
TEMPERATURE (°C)
VC = 1.25V
–100
0
100
FB PIN ERROR VOLTAGE (mV)
200
8636 G30
RT Programmed Switching
Frequency
PG Low Thresholds
9.5
0
–125
8636 G29
10.0
6.0
–50 –25
0
1.4
–50 –25
PG High Thresholds
7.0
125
–375
8636 G28
8.0
250
1.5
–6.0
250
–6.5
225
200
–7.0
RT PIN RESISTOR (kΩ)
0
375
VC PIN CURRENT (µA)
SS PIN CURRENT (µA)
FB VOLTAGE (V)
0.8
500
VSS = 0.5V
2.1
1.0
0
LT8637 Error Amp Output Current
Soft–Start
Current
Soft-Start Current
1.2
–7.5
FB RISING
–8.0
–8.5
FB FALLING
–9.0
175
150
125
100
75
50
–9.5
25
–10.0
–50 –25
0
8636 G31
0
0.2
25 50 75 100 125 150
TEMPERATURE (°C)
8636 G32
0.6
1.4 1.8 2.2 2.6
1
SWITCHING FREQUENCY (MHz)
3
8636 G33
Bias Pin Current
3.4
8.0
3.2
3.0
2.8
2.4
–50
7.5
7.0
6.5
VBIAS = 5V
VOUT = 5V
ILOAD = 1A
fSW = 1MHz
6.0
2.6
–25
0
25
50
75
TEMPERATURE (°C)
100
125
Bias Pin Current
25
BIAS PIN CURRENT (mA)
8.5
BIAS PIN CURRENT (mA)
INPUT VOLTAGE (V)
Minimum Input Voltage
3.6
5.5
5
10
15
20 25 30 35
INPUT VOLTAGE (V)
40
45
8636 G35
8636 G34
20
VBIAS = 5V
VOUT = 5V
VIN = 12V
ILOAD = 1A
15
10
5
0
0.2
0.6
1
1.4 1.8 2.2 2.6
SWITCHING FREQUENCY (MHz)
3.0
8636 G36
Rev. C
8
For more information www.analog.com
LT8636/LT8637
TYPICAL PERFORMANCE CHARACTERISTICS
Case Temperature Rise vs 7A
Pulsed Load
Case Temperature Rise
80
CASE TEMPERATURE RISE (°C)
60
CASE TEMPERATURE RISE (°C)
VIN = 12V, fSW = 1MHz
VIN = 24V, fSW = 1MHz
VIN = 12V, fSW = 2MHz
VIN = 24V, fSW = 2MHz
70
DEMO BOARD IN STILL AIR
50 L = XEL6030, 1.5µH
40
30
20
DC2918A DEMO BOARD
120 VIN = 12V
VOUT = 5V
105 fSW = 2MHz
STANDBY LOAD = 0.25A
90 1kHz PULSED LOAD = 7A
10
0
Switching Rising Edge
135
VSW
2V/DIV
75
60
45
30
15
0
1
2
3
LOAD CURRENT (A)
4
0
5
0
0.2
0.4
0.6
0.8
DUTY CYCLE OF 7A LOAD
Switching Waveforms, Full
Frequency Continuous Operation
VSW
5V/DIV
500ns/DIV
Switching Waveforms, Burst
Mode Operation
IL
1A/DIV
VSW
5V/DIV
VSW
10V/DIV
FRONT PAGE APPLICATION
12VIN TO 5VOUT AT 1A
8636 G41
5µs/DIV
FRONT PAGE APPLICATION
12VIN TO 5VOUT AT 10mA
VSYNC = 0V
500ns/DIV
FRONT PAGE APPLICATION
36VIN TO 5VOUT AT 1A
8636 G42
LT8637 Transient Response;
External Compensation
LT8636 Transient Response;
Internal Compensation
ILOAD
2A/DIV
ILOAD
2A/DIV
VOUT
100mV/DIV
VOUT
100mV/DIV
FRONT PAGE APPLICATION
2A TO 4A TRANSIENT
12VIN, 5VOUT
fSW = 2MHz
COUT = 100µF, CLEAD = 10pF
8636 G39
Switching Waveforms
IL
500mA/DIV
8636 G40
20µs/DIV
1
2ns/DIV
8636 G38
8636 G37
IL
1A/DIV
VIN = 12V
ILOAD = 2A
8636 G43
20µs/DIV
8636 G44
2A TO 4A TRANSIENT
12VIN, 5VOUT
fSW = 2MHz
CC = 330pF, RC = 8.45k
COUT = 100µF, CLEAD = 4.7pF
Rev. C
For more information www.analog.com
9
LT8636/LT8637
TYPICAL PERFORMANCE CHARACTERISTICS
LT8636 Transient Response;
100mA to 1.1A Transient
LT8637 Transient Response;
100mA to 1.1A Transient
ILOAD
1A/DIV
ILOAD
1A/DIV
Burst Mode OPERATION
Burst Mode OPERATION
VOUT
100mV/DIV
VOUT
100mV/DIV
FCM
FCM
8636 G45
VIN
2V/DIV
VOUT
2V/DIV
8636 G46
FRONT PAGE APPLICATION
100mA TO 1.1A TRANSIENT
12VIN, 5VOUT, fSW = 1MHz
COUT = 100µF
50µs/DIV
CC = 330pF, RC = 6.49k, CLEAD = 4.7pF
100mA TO 1.1A TRANSIENT
12VIN, 5VOUT, fSW = 1MHz
COUT = 100µF
Start-Up Dropout Performance
Start-Up Dropout Performance
50µs/DIV
VIN
VOUT
100ms/DIV
2.5Ω LOAD
(2A IN REGULATION)
VIN
VIN
2V/DIV
VOUT
VOUT
2V/DIV
8636 G47
100ms/DIV
20Ω LOAD
(250mA IN REGULATION)
8636 G48
Rev. C
10
For more information www.analog.com
LT8636/LT8637
TYPICAL PERFORMANCE CHARACTERISTICS
Conducted
EMI Performance
Conducted EMI
Performance
60
50
AMPLITUDE (dBµV/m)
40
30
20
10
0
–10
–20
SPREAD SPECTRUM MODE
FIXED FREQUENCY MODE
–30
–40
0
3
6
9
12
15
18
FREQUENCY (MHz)
21
24
27
DC2918A DEMO BOARD
(WITH EMI FILTER INSTALLED)
14V INPUT TO 5V OUTPUT AT 5A, fSW = 2MHz
30
8636 G49
Radiated EMI Performance
Radiated EMI Performance
(CISPR25
Radiated
Emission
Test
with
Class
5 Peak
Limits)
(CISPR25 Radiated
Emission
Test
with
Class
5 Peak
Limits)
50
VERTICAL POLARIZATION
PEAK DETECTOR
45
AMPLITUDE (dBµV/m)
40
35
30
25
20
15
10
5
CLASS 5 PEAK LIMIT
SPREAD SPECTRUM MODE
FIXED FREQUENCY MODE
0
–5
0
100
200
300
400
500
600
FREQUENCY (MHz)
700
800
DC2918A DEMO BOARD
(WITH EMI FILTER INSTALLED)
14V INPUT TO 5V OUTPUT AT 5A, fSW = 2MHz
900
1000
8636 G50
Rev. C
For more information www.analog.com
11
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
below 1V, INTVCC has fallen too low, VIN is too low, or
thermal shutdown. PG is valid when VIN is above 3.4V.
BIAS (Pin 2): 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 to 25V 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.
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.
INTVCC (Pin 3): 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 BIAS > 3.1V,
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 capacitor 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.
NC (Pins 5, 12): No Connect. This pin is not connected
to internal circuitry and can be tied anywhere on the PCB,
typically ground.
VIN (Pins 6, 11): The VIN pins supply current to the
LT8636/LT8637 internal circuitry and to the internal topside power switch. The LT8636/LT8637 requires the use
of multiple VIN bypass capacitors. Two small 1µF capacitors should be placed as close as possible to the LT8636/
LT8637, one capacitor on each side of the device (CIN1,
CIN2). A third capacitor with a larger value, 2.2µF or higher,
should be placed near CIN1 or CIN2. See Applications
Information section for sample layout.
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.
SW (Pins 8–10): The SW pins are the outputs of the internal 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.
EN/UV (Pin 14): The LT8636/LT8637 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 LT8636/LT8637 will shut
down.
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 3.1V
OR GND
VOUT
1.8V
5A
10pF
866k
FB
INTVCC
RT
1µH
0.1µF
BIAS
1µF
17.8k
1µF
0603
1M
GND
100µF
1210
X5R/X7R
8636 TA02
fSW = 2MHz
L: XEL6030
PINS NOT USED IN THIS CIRCUIT:
CLKOUT, PG, SYNC/MODE
RELATED PARTS
PART
DESCRIPTION
COMMENTS
LT8640S/
LT8643S
42V, 6A Synchronous Step-Down Silent Switcher 2 with IQ = 2.5μA
VIN(MIN) = 3.4V, VIN(MAX) = 42V, VOUT(MIN) = 0.97V, IQ = 2.5µA,
ISD < 1µA, 4mm × 4mm LQFN-24
LT8640/
LT8640-1
42V, 5A, 96% Efficiency, 3MHz Synchronous MicroPower Step-Down
DC/DC Converter with IQ = 2.5μA
VIN(MIN) = 3.4V, VIN(MAX) = 42V, VOUT(MIN) = 0.97V, IQ = 2.5µA,
ISD < 1µA, 3mm × 4mm QFN-18
LT8645S/
LT8646S
65V, 8A, Synchronous Step-Down Silent Switcher 2 with IQ = 2.5μA
VIN(MIN) = 3.4V, VIN(MAX) = 65V, VOUT(MIN) = 0.97V, IQ = 2.5µA,
ISD < 1µA, 4mm × 6mm LQFN-32
LT8641
65V, 3.5A, 95% Efficiency, 3MHz Synchronous MicroPower Step-Down
DC/DC Converter with IQ = 2.5μA
VIN(MIN) = 3V, VIN(MAX) = 65V, VOUT(MIN) = 0.81V, IQ = 2.5µA,
ISD < 1µA, 3mm × 4mm QFN-18
LT8609/
LT8609A
42V, 2A, 94% Efficiency, 2.2MHz Synchronous MicroPower Step-Down
DC/DC Converter with IQ = 2.5µA
VIN(MIN) = 3V, VIN(MAX) = 42V, VOUT(MIN) = 0.8V, IQ = 2.5µA,
ISD < 1µA, MSOP-10E
LT8610A/
LT8610AB
42V, 3.5A, 96% Efficiency, 2.2MHz Synchronous MicroPower StepDown DC/DC Converter with IQ = 2.5µA
VIN(MIN) = 3.4V, VIN(MAX) = 42V, VOUT(MIN) = 0.97V, IQ = 2.5µA,
ISD < 1µA, MSOP-16E
LT8610AC
42V, 3.5A, 96% Efficiency, 2.2MHz Synchronous MicroPower StepDown DC/DC Converter with IQ = 2.5µA
VIN(MIN) = 3V, VIN(MAX) = 42V, VOUT(MIN) = 0.8V, IQ = 2.5µA,
ISD < 1µA, MSOP-16E
LT8610
42V, 2.5A, 96% Efficiency, 2.2MHz Synchronous MicroPower StepDown DC/DC Converter with IQ = 2.5µA
VIN(MIN) = 3.4V, VIN(MAX) = 42V, VOUT(MIN) = 0.97V, IQ = 2.5µA,
ISD < 1µA, MSOP-16E
LT8616
42V, Dual 2.5A + 1.5A, 95% Efficiency, 2.2MHz Synchronous
MicroPower Step-Down DC/DC Converter with IQ = 5µA
VIN(MIN) = 3.4V, VIN(MAX) = 42V, VOUT(MIN) = 0.8V, IQ = 5µA,
ISD < 1µA, TSSOP-28E, 3mm × 6mm QFN-28
LT8620
65V, 2.5A, 94% Efficiency, 2.2MHz Synchronous MicroPower StepDown DC/DC Converter with IQ = 2.5µA
VIN(MIN) = 3.4V, VIN(MAX) = 65V, VOUT(MIN) = 0.97V, IQ = 2.5µA,
ISD < 1µA, MSOP-16E, 3mm × 5mm QFN-24
LT8614
42V, 4A, 96% Efficiency, 2.2MHz Synchronous Silent Switcher StepDown DC/DC Converter with IQ = 2.5µA
VIN(MIN) = 3.4V, VIN(MAX) = 42V, VOUT(MIN) = 0.97V, IQ = 2.5µA,
ISD < 1µA, 3mm × 4mm QFN18
LT8612
42V, 6A, 96% Efficiency, 2.2MHz Synchronous MicroPower Step-Down
DC/DC Converter with IQ = 2.5µA
VIN(MIN) = 3.4V, VIN(MAX) = 42V, VOUT(MIN) = 0.97V, IQ = 3.0µA,
ISD < 1µA, 3mm × 6mm QFN-28
LT8602
42V, Quad Output (2.5A + 1.5A + 1.5A + 1.5A) 95% Efficiency, 2.2MHz
Synchronous MicroPower Step-Down DC/DC Converter with IQ = 25µA
VIN(MIN) = 3V, VIN(MAX) = 42V, VOUT(MIN) = 0.8V, IQ = 2.5µA,
ISD < 1µA, 6mm × 6mm QFN-40
Rev. C
32
12/20
For more information www.analog.com
www.analog.com
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