LT8636
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
n Output Ripple < 10mV
P-P
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 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
The LT8636’s ultralow 2.5µA quiescent current—with the
output in full regulation—enables applications requiring
highest efficiency at very small load currents. A CLKOUT
pin enables synchronizing other regulators to the LT8636.
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.
All registered trademarks and trademarks are the property of their respective owners. Protected
by U.S. patents, including 8823345.
APPLICATIONS
n
n
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
BST
0.1µF
SW
3.3µH
VOUT
5V
5A
BIAS
1µF
41.2k
fSW = 1MHz
INTVCC
10pF
RT
2.8
EFFICIENCY
100µF
2.0
80
1.6
8636 TA01a
1.2
75
POWER LOSS
65
60
0.5
243k
2.4
85
70
1M
FB
GND
95
90
1µF
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. B
Document Feedback
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1
LT8636
ABSOLUTE MAXIMUM RATINGS
PIN CONFIGURATION
(Note 1)
FB
FB
TR/SS
RT
TOP VIEW
20
19
18
17
PG
1
16 CLKOUT
BIAS
2
15 SYNC/MODE
INTVCC
3
GND
4
NC
5
12 NC
VIN
6
11 VIN
14 EN/UV
21
GND
7
8
9
10
SW
SW
SW
13 GND
BST
VIN, EN/UV, PG...........................................................42V
BIAS...........................................................................25V
FB, TR/SS ...................................................................4V
SYNC/MODE Voltage ..................................................6V
Operating Junction Temperature Range (Note 2)
LT8636E............................................. –40°C to 125°C
LT8636J............................................. –40°C to 150°C
LT8636H............................................. –40°C to 150°C
Storage Temperature Range................... –65°C to 150°C
Maximum Reflow (Package Body) Temperature...... 260°C
LQFN PACKAGE
20-LEAD (4mm × 3mm × 0.94mm)
JEDEC BOARD: θJA = 41°C/W, ΨJT = 1.1°C/W,
θJC(top) = 50.6°C/W, θJC(pad) = 8.0°C/W, (NOTE 3)
DEMO BOARD: θJA = 26°C/W
EXPOSED PAD (PIN 21) IS GND, SHOULD BE SOLDERED TO PCB
ORDER INFORMATION
PART NUMBER
PART MARKING*
FINISH CODE
PAD FINISH
8636
e4
Au (RoHS)
LT8636EV#PBF
LT8636JV#PBF
LT8636HV#PBF
PACKAGE
TYPE**
MSL
RATING
LQFN (Laminate Package
with QFN Footprint)
3
TEMPERATURE RANGE
–40°C to 125°C
–40°C to 150°C
–40°C to 150°C
AUTOMOTIVE PRODUCTS***
LT8636EV#WPBF
LT8636JV#WPBF
LT8636JV#WTRPBF
–40°C to 125°C
8636
e4
Au (RoHS)
LQFN (Laminate Package
with QFN Footprint)
LT8636HV#WPBF
3
–40°C to 150°C
–40°C to 150°C
–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 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.
Rev. B
2
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LT8636
The
l denotes the specifications which apply over the full operating
ELECTRICAL
CHARACTERISTICS
temperature range, otherwise specifications are at TA = 25°C.
PARAMETER
CONDITIONS
MIN
Minimum Input Voltage
VIN Quiescent Current in Shutdown
VEN/UV = 0V
VIN Quiescent Current in Sleep
VEN/UV = 2V, VFB > 0.97V, VSYNC = 0V
TYP
MAX
l
3.0
3.4
V
l
1
1
3
10
µA
µA
l
1.7
1.7
4
10
µA
µA
220
390
µA
0.970
0.970
0.974
0.982
V
V
0.004
0.02
%/V
VIN Current in Regulation
VOUT = 0.97V, VIN = 6V, ILOAD = 1mA, VSYNC = 0
Feedback Reference Voltage
VIN = 6V
VIN = 6V
l
VIN = 4.0V to 36V
l
Feedback Voltage Line Regulation
Feedback Pin Input Current
VFB = 1V
BIAS Pin Current Consumption
VBIAS = 3.3V, fSW = 2MHz
Minimum On-Time
ILOAD = 1.5A, SYNC = 0V
ILOAD = 1.5A, SYNC = 2V
0.966
0.956
–20
l
l
Minimum Off-Time
Oscillator Frequency
RT = 221k
RT = 60.4k
RT = 18.2k
Top Power NMOS On-Resistance
ISW = 1A
20
14
l
l
l
180
665
1.8
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
30
30
50
45
ns
ns
80
110
ns
210
700
1.95
240
735
2.1
kHz
kHz
MHz
10
mΩ
12.5
27
–3
l
0.94
EN/UV Pin Hysteresis
nA
mA
66
Top Power NMOS Current Limit
UNITS
mΩ
3
1.0
1.06
40
–20
A
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
%
80
nA
700
2000
Ω
0.9
1.2
2.55
1.4
2.9
V
V
V
PG Hysteresis
20
0.2
–80
nA
%
PG Leakage
VPG = 3.3V
PG Pull-Down Resistance
VPG = 0.1V
l
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
22
%
Spread Spectrum Modulation Frequency
VSYNC = 3.3V
3
kHz
TR/SS Source Current
l
TR/SS Pull-Down Resistance
Fault Condition, TR/SS = 0.1V
VIN to Disable Forced Continuous Mode
VIN Rising
0.7
2.2
1.2
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
1.9
37
µA
Ω
39
V
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. Operating lifetime is derated at junction temperatures
greater than 125°C. The junction temperature (TJ, in °C) is calculated from
Rev. B
For more information www.analog.com
3
LT8636
ELECTRICAL CHARACTERISTICS
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.
TYPICAL PERFORMANCE CHARACTERISTICS
12VIN to 5VOUT Efficiency
vs Frequency
12VIN to 3.3VOUT Efficiency
vs Frequency
95
EFFICIENCY
100
3.2
2.8
95
2.8
2.4
90
2.0
80
1.6
1.2
75
POWER LOSS
70
65
60
0.5
1
L = XEL6060 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)
2.4
EFFICIENCY
85
2.0
80
1.6
1.2
75
POWER LOSS
70
65
60
0.5
1
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 G02
8636 G01
Efficiency at 5VOUT
L = XEL6060, 2.7µH
95
90
EFFICIENCY
2.7
95
2.4
90
2.1
80
1.8
75
1.5
70
1.2
POWER LOSS
65
fSW = 1MHz
60
55
50
0
1
2
3
LOAD CURRENT (A)
0.9
0.6
VIN = 12V
VIN = 24V 0.3
VIN = 36V
0
4
5
L = XEL6060, 2.2µH
3.0
2.7
2.4
EFFICIENCY
85
2.1
80
1.8
75
1.5
70
65
fSW = 1MHz
60
55
50
1.2
POWER LOSS
0
8636 G03
1
2
3
LOAD CURRENT (A)
0.9
POWER LOSS (W)
85
100
POWER LOSS (W)
EFFICIENCY (%)
Efficiency at 3.3VOUT
3.0
EFFICIENCY (%)
100
POWER LOSS (W)
85
POWER LOSS (W)
EFFICIENCY (%)
90
3.2
EFFICIENCY (%)
100
0.6
VIN = 12V
VIN = 24V 0.3
VIN = 36V
0
4
5
8636 G04
Rev. B
4
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LT8636
TYPICAL PERFORMANCE CHARACTERISTICS
Efficiency at 5VOUT
100
Efficiency at 3.3VOUT
94
80
80
92
70
60
Burst Mode OPERATION
fSW = 1MHz
L = XEL6060, 4.7µH
50
20
0.01
0.1
1
10
100
LOAD CURRENT (mA)
60
Burst Mode OPERATION
fSW = 1MHz
L = XEL6060, 4.7µH
50
40
VIN = 12V
VIN = 24V
VIN = 36V
30
70
20
0.01
0.1
1
10
100
LOAD CURRENT (mA)
8636 G05
90
VIN = 24V
80
75
65
VOUT = 5V
ILOAD = 10mA
L = IHLP3232DZ-01
1
2
3
4
5
6
INDUCTOR VALUE (µH)
7
1000
EN Pin Thresholds
979
1.03
977
1.02
975
1.01
973
971
969
967
EN RISING
1.00
0.99
0.98
EN FALLING
0.97
965
0.96
963
961
–50 –25
8
0
8636 G10
25 50 75 100 125 150
TEMPERATURE (°C)
0.95
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
8636 G12
8636 G11
Load Regulation
Line Regulation
0.15
3
8636 G09
EN THRESHOLD (V)
REFERENCE VOLTAGE (mV)
VIN = 12V
70
86
Reference Voltage
100
85
88
8636 G07
Burst Mode Operation Efficiency
vs Inductor Value
95
90
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)
VIN = 12V
VIN = 24V
VIN = 36V
30
1000
EFFICIENCY (%)
90
40
EFFICIENCY (%)
Efficiency vs Frequency
96
90
EFFICIENCY (%)
EFFICIENCY (%)
100
No-Load Supply Current
0.12
4.0
0.10
0
0.05
0
1
2
3
4
LOAD CURRENT (A)
5
0.06
0.04
0.02
0.00
–0.02
–0.04
VOUT = 5V
VIN = 12V
VSYNC = 0V
–0.10
INPUT CURRENT (µA)
0.05
–0.15
3.5
0.08
CHANGE IN VOUT (%)
CHANGE IN VOUT (%)
0.10
VOUT = 5V
ILOAD = 1A
–0.06
6
8636 G13
–0.08
5
10
15
20 25 30 35
INPUT VOLTAGE (V)
40
45
8636 G15
3.0
2.5
2.0
VOUT = 3.3V
L = 4.7µH
BIAS = VOUT
IN REGULATION
1.5
1.0
0
5
10
15 20 25 30 35
INPUT VOLTAGE (V)
40
45
8636 G17
Rev. B
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5
LT8636
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
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. B
6
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LT8636
TYPICAL PERFORMANCE CHARACTERISTICS
PG High Thresholds
Soft–Start
Current
Soft-Start Current
VSS = 0.5V
SS PIN CURRENT (µA)
2.0
1.9
1.8
1.7
1.6
1.5
1.4
–50 –25
0
–6.0
9.5
9.0
8.5
FB RISING
8.0
7.5
FB FALLING
7.0
6.5
6.0
–50 –25
25 50 75 100 125 150
TEMPERATURE (°C)
PG THRESHOLD OFFSET FROM VREF (%)
2.1
PG Low Thresholds
10.0
PG THRESHOLD OFFSET FROM VREF (%)
2.2
0
25 50 75 100 125 150
TEMPERATURE (°C)
–6.5
–7.0
–7.5
FB RISING
–8.0
–8.5
FB FALLING
–9.0
–9.5
–10.0
–50 –25
0
8636 G31
8636 G29
RT Programmed Switching
Frequency
8636 G32
Minimum Input Voltage
250
25 50 75 100 125 150
TEMPERATURE (°C)
Bias Pin Current
3.6
8.5
3.4
8.0
175
INPUT VOLTAGE (V)
RT PIN RESISTOR (kΩ)
200
150
125
100
75
50
BIAS PIN CURRENT (mA)
225
3.2
3.0
2.8
0
0.2
0.6
1.4 1.8 2.2 2.6
1
SWITCHING FREQUENCY (MHz)
2.4
–50
3
–25
0
25
50
75
TEMPERATURE (°C)
100
Bias Pin Current
80
5
3.0
8636 G36
10
15
20 25 30 35
INPUT VOLTAGE (V)
40
60
DEMO BOARD IN STILL AIR
50 L = XEL6030, 1.5µH
40
30
20
0
45
135
10
0.6
1
1.4 1.8 2.2 2.6
SWITCHING FREQUENCY (MHz)
5
Case Temperature Rise vs 7A
Pulsed Load
VIN = 12V, fSW = 1MHz
VIN = 24V, fSW = 1MHz
VIN = 12V, fSW = 2MHz
VIN = 24V, fSW = 2MHz
70
10
VBIAS = 5V
VOUT = 5V
ILOAD = 1A
fSW = 1MHz
8636 G35
CASE TEMPERATURE RISE (°C)
VBIAS = 5V
VOUT = 5V
VIN = 12V
ILOAD = 1A
15
0
0.2
5.5
125
Case Temperature Rise
CASE TEMPERATURE RISE (°C)
BIAS PIN CURRENT (mA)
20
6.5
8636 G34
8636 G33
25
7.0
6.0
2.6
25
7.5
DC2918A DEMO BOARD
120 VIN = 12V
VOUT = 5V
105 fSW = 2MHz
STANDBY LOAD = 0.25A
90 1kHz PULSED LOAD = 7A
75
60
45
30
15
0
1
2
3
LOAD CURRENT (A)
4
5
8636 G37
0
0
0.2
0.4
0.6
0.8
DUTY CYCLE OF 7A LOAD
1
8636 G38
Rev. B
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7
LT8636
TYPICAL PERFORMANCE CHARACTERISTICS
Switching Waveforms, Full
Frequency Continuous Operation
Switching Rising Edge
IL
1A/DIV
IL
500mA/DIV
VSW
2V/DIV
VSW
5V/DIV
2ns/DIV
VIN = 12V
ILOAD = 2A
VSW
5V/DIV
8636 G39
8636 G40
500ns/DIV
Switching Waveforms
8636 G41
FRONT PAGE APPLICATION
12VIN TO 5VOUT AT 1A
5µs/DIV
FRONT PAGE APPLICATION
12VIN TO 5VOUT AT 10mA
VSYNC = 0V
Transient Response; 2A to 4A
Transient
Transient Response; 100mA to
1.1A Transient
ILOAD
2A/DIV
IL
1A/DIV
Switching Waveforms, Burst
Mode Operation
ILOAD
1A/DIV
Burst Mode OPERATION
VOUT
100mV/DIV
VSW
10V/DIV
VOUT
100mV/DIV
FCM
500ns/DIV
FRONT PAGE APPLICATION
36VIN TO 5VOUT AT 1A
8636 G42
VOUT
2V/DIV
50µs/DIV
FRONT PAGE APPLICATION
2A TO 4A TRANSIENT
12VIN, 5VOUT
fSW = 2MHz
COUT = 100µF, CLEAD = 10pF
Start-Up Dropout Performance
VIN
2V/DIV
8636 G43
20µs/DIV
FRONT PAGE APPLICATION
100mA TO 1.1A TRANSIENT
12VIN, 5VOUT, fSW = 1MHz
COUT = 100µF
Start-Up Dropout Performance
VIN
VIN
VIN
2V/DIV
VOUT
100ms/DIV
2.5Ω LOAD
(2A IN REGULATION)
8636 G45
VOUT
VOUT
2V/DIV
8636 G47
100ms/DIV
20Ω LOAD
(250mA IN REGULATION)
8636 G48
Rev. B
8
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LT8636
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. B
For more information www.analog.com
9
LT8636
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 internal circuitry and to the internal topside
power switch. The LT8636 requires the use of multiple
VIN bypass capacitors. Two small 1µF capacitors should
be placed as close as possible to the LT8636, 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 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 will shut down.
SYNC/MODE (Pin 15): For the LT8636, 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
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LT8640/
LT8640-1
42V, 5A, 96% Efficiency, 3MHz Synchronous MicroPower Step-Down
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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
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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. B
26
04/20
For more information www.analog.com
www.analog.com
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