LT8610

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Technical content

Rev. CFor more information www.analog.comDocument Feedback TYPICAL APPLICATION

FEATURES

42V, 5A/7A Peak Synchronous Step-Down Silent Switcher with 2.5µA Quiescent Current

DESCRIPTION

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. 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 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. 5V, 5A Step-Down Converter

APPLICATIONS

n 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, 12VIN to 5VOUT n Up to 95% Efficiency at 2MHz, 12VIN to 5VOUT n Wide Input Voltage Range: 3.4V to 42V n 5A Maximum Continuous, 7A Peak T ransient Output n Ultralow Quiescent Current Burst Mode® Operation n 2.5µA IQ Regulating 12VIN to 3.3VOUT (LT8636) n Output Ripple < 10mVP-P n External Compensation: Fast T ransient 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 n Automotive and Industrial Supplies n General Purpose Step-Down All registered trademarks and trademarks are the property of their respective owners. Protected by U.S. patents, including 8823345. 12VIN to 5VOUT Efficiency EFFICIENCY POWER LOSS 1MHz, L = 2.7µH 2MHz, L = 1.5µH 3MHz, L = 1µH LOAD CURRENT (A) 0.5 1.5 2.5 3.5 4.5 100 0.4 0.8 1.2 1.6 2.0 2.4 2.8 3.2 EFFICIENCY (%) POWER LOSS (W)

8636 TA01b

8636 TA01a

100µF 1µF VOUT 4.7µF 1µF 1µF 0.1µF 10pF 3.3µH VIN 5.7V TO 42V 41.2k 243k fSW = 1MHz

Rev. C For more information www.analog.com PIN CONFIGURATION ABSOLUTE MAXIMUM RATINGS ORDER INFORMATION PART NUMBER PART MARKING* FINISH CODE PAD FINISH PACKAGE TYPE** MSL RATING TEMPERATURE RANGE LT8636EV#PBF 8636 e4 Au (RoHS) LQFN (Laminate Package with QFN Footprint) 3 –40°C to 125°C LT8636JV#PBF –40°C to 150°C LT8636HV#PBF –40°C to 150°C LT8636MPV#PBF –55°C to 150°C LT8637EV#PBF 8637 –40°C to 125°C LT8637JV#PBF –40°C to 150°C (Note 1) Operating Junction Temperature Range (Note 2) LT8636 LT8637 17181920 7 8 9 10 TOP VIEW 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 PG BIAS INTVCC GND NC VIN CLKOUT SYNC/MODE EN/UV GND NC VIN BST SW SW SW FB FB TR/SS RT GND 17181920 7 8 9 10 TOP VIEW LQFN PACKAGE 20-LEAD (4mm × 3mm × 0.94mm) PG BIAS INTVCC GND NC VIN CLKOUT SYNC/MODE EN/UV GND NC VIN BST SW SW SW FB VC TR/SS RT GND 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

Rev. CFor more information www.analog.com PART NUMBER PART MARKING* FINISH CODE PAD FINISH PACKAGE TYPE MSL RATING TEMPERATURE RANGE AUTOMOTIVE PRODUCTS* LT8636EV#WPBF 8636 e4 Au (RoHS) LQFN (Laminate Package with QFN Footprint) 3 –40°C to 125°C LT8636JV#WPBF –40°C to 150°C LT8636JV#WTRPBF –40°C to 150°C LT8636HV#WPBF –40°C to 150°C LT8637EV#WPBF 8637 –40°C to 125°C LT8637JV#WPBF –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. ORDER INFORMATION ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. PARAMETER CONDITIONS MIN TYP MAX UNITS Minimum Input Voltage l 3.0 3.4 V VIN Quiescent Current in Shutdown VEN/UV = 0V l µA µA L T8636 VIN Quiescent Current in Sleep (Internal Compensation) VEN/UV = 2V, VFB > 0.97V, VSYNC = 0V l 1.7 1.7 µA µA L T8637 VIN Quiescent Current in Sleep (External Compensation) VEN/UV = 2V, VFB > 0.97V, VSYNC = 0V, VBIAS = 0V l 230 230 290 340 µA µA VEN/UV = 2V, VFB > 0.97V, VSYNC = 0V, VBIAS = 5V 19 25 µA L T8637 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 0.966 0.956 0.970 0.970 0.974 0.982 V V Feedback Voltage Line Regulation VIN = 4.0V to 36V l 0.004 0.02 %/V Feedback Pin Input Current VFB = 1V –20 20 nA L T8637 Error Amp T ransconductance VC = 1.25V 1.7 mS L T8637 Error Amp Gain 260 L T8637 VC Source Current VFB = 0.77V, VC = 1.25V 350 µA L T8637 VC Sink Current VFB = 1.17V, VC = 1.25V 350 µA L T8637 VC Pin to Switch Current Gain 5 A/V L T8637 VC Clamp Voltage 2.6 V BIAS Pin Current Consumption VBIAS = 3.3V, fSW = 2MHz 14 mA

Rev. C For more information www.analog.com 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 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. PARAMETER CONDITIONS MIN TYP MAX UNITS Minimum On-Time ILOAD = 1.5A, SYNC = 0V ILOAD = 1.5A, SYNC = 2V l l ns ns Minimum Off-Time 80 110 ns Oscillator Frequency RT = 221k RT = 60.4k RT = 18.2k l l l 180 665 1.8 210 700 1.95 240 735 2.1 kHz kHz MHz Top Power NMOS On-Resistance ISW = 1A 66 mΩ Top Power NMOS Current Limit l 7.5 10 12.5 A Bottom Power NMOS On-Resistance VINTVCC = 3.4V, ISW = 1A 27 mΩ SW Leakage Current VIN = 42V, VSW = 0V, 42V –3 3 µA EN/UV Pin Threshold EN/UV Rising l 0.94 1.0 1.06 V EN/UV Pin Hysteresis 40 mV EN/UV Pin Current VEN/UV = 2V –20 20 nA PG Upper Threshold Offset from VFB VFB Falling l 5 7.5 10.25 % PG Lower Threshold Offset from VFB VFB Rising l –10.75 –8 –5.25 % PG Hysteresis 0.2 % PG Leakage VPG = 3.3V –80 80 nA PG Pull-Down Resistance VPG = 0.1V l 700 2000 Ω 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 0.7 2.2 0.9 1.2 2.55 1.4 2.9 V V V 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 1.2 1.9 2.6 µA TR/SS Pull-Down Resistance Fault Condition, TR/SS = 0.1V 200 Ω VIN to Disable Forced Continuous Mode VIN Rising 35 37 39 V ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C.

Rev. CFor more information www.analog.com TYPICAL PERFORMANCE CHARACTERISTICS 12VIN to 3.3VOUT Efficiency vs Frequency 12VIN to 5VOUT Efficiency vs Frequency Efficiency at 5VOUT Efficiency at 3.3VOUT L = XEL6060 EFFICIENCY POWER LOSS 1MHz, L = 2.7µH 2MHz, L = 1.5µH 3MHz, L = 1µH LOAD CURRENT (A) 0.5 1.5 2.5 3.5 4.5 100 0.4 0.8 1.2 1.6 2.0 2.4 2.8 3.2 EFFICIENCY (%) POWER LOSS (W)

8636 G01

L = XEL6060 EFFICIENCY POWER LOSS 1MHz, L = 2.2µH 2MHz, L = 1µH 3MHz, L = 1µH LOAD CURRENT (A) 0.5 1.5 2.5 3.5 4.5 100 0.4 0.8 1.2 1.6 2.0 2.4 2.8 3.2 EFFICIENCY (%) POWER LOSS (W)

8636 G02

L = XEL6060, 2.7µH EFFICIENCY POWER LOSS f SW = 1MHz V IN = 12V V IN = 24V V IN = 36V LOAD CURRENT (A) 100 0.3 0.6 0.9 1.2 1.5 1.8 2.1 2.4 2.7 3.0 EFFICIENCY (%) POWER LOSS (W)

8636 G03

L = XEL6060, 2.2µH EFFICIENCY POWER LOSS f SW = 1MHz V IN = 12V V IN = 24V V IN = 36V LOAD CURRENT (A) 100 0.3 0.6 0.9 1.2 1.5 1.8 2.1 2.4 2.7 3.0 EFFICIENCY (%) POWER LOSS (W)

8636 G04

LT8636 Low Load Efficiency at 5VOUT f SW = 1MHz L = XEL6060, 4.7µH Burst Mode OPERATION V IN = 12V V IN = 24V V IN = 36V LOAD CURRENT (mA) 0.01 0.1 100 1000 100 EFFICIENCY (%)

8636 G05

LT8636 Low Load Efficiency at 3.3VOUT Efficiency vs Frequency VIN = 12V V OUT = 3.3V I LOAD = 2A L = IHLP3232DZ-01, 4.7µH SWITCHING FREQUENCY (MHz) 0.5 1.5 2.5 EFFICIENCY (%)

8636 G09

V IN = 12V V IN = 24V V IN = 36V LOAD CURRENT (mA) 0.01 0.1 100 1000 100 EFFICIENCY (%)

8636 G07

f SW = 1MHz L = XEL6060, 4.7µH Burst Mode OPERATION f SW = 1MHz L = IHLP3232DZ–01, 4.7µH V IN = 12V V IN = 24V V IN = 36V LOAD CURRENT (mA) 0.1 100 1000 100 EFFICIENCY (%)

8636 G06

f SW = 1MHz L = IHLP3232DZ–01, 4.7µH V IN = 12V V IN = 24V V IN = 36V LOAD CURRENT (mA) 0.1 100 1000 100 EFFICIENCY (%)

8636 G08

LT8637 Low Load Efficiency at 5VOUT LT8637 Low Load Efficiency at 3.3VOUT

Rev. C For more information www.analog.com TYPICAL PERFORMANCE CHARACTERISTICS Burst Mode Operation Efficiency vs Inductor Value (LT8636) Reference Voltage EN Pin Thresholds LT8636 Load Regulation LT8636 Line Regulation LT8636 No-Load Supply Current V OUT = 5V I LOAD = 10mA L = IHLP3232DZ-01 V IN = 12V V IN = 24V INDUCTOR VALUE (µH) 100 EFFICIENCY (%) vs Inductor Value

8636 G10

TEMPERATURE (°C) –50 –25 100 125 150 961 963 965 967 969 971 973 975 977 979 REFERENCE VOL TAGE (mV) Reference Voltage

8636 G11

TEMPERATURE (°C) –50 –25 100 125 150 0.95 0.96 0.97 0.98 0.99 1.00 1.01 1.02 1.03 EN THRESHOLD (V) EN Pin Thresholds

8636 G12

V OUT = 5V V SYNC = 0V V IN = 12V LOAD CURRENT (A) –0.15 –0.10 0.05 0.05 0.10 0.15 CHANGE IN V OUT (%)

8636 G13

V OUT = 5V I LOAD = 1A INPUT VOL TAGE (V) –0.08 –0.06 –0.04 –0.02 0.00 0.02 0.04 0.06 0.08 0.10 0.12 CHANGE IN V OUT (%)

8636 G15

V OUT = 3.3V L = 4.7µH BIAS = VOUT IN REGULATION INPUT VOL TAGE (V) 1.0 1.5 2.0 2.5 3.0 3.5 4.0 INPUT CURRENT (µA)

8636 G17

LOAD CURRENT (A) –0.40 –0.30 –0.20 –0.10 0.00 0.10 0.20 0.30 0.40 CHANGE IN V OUT (%)

8636 G14

V OUT = 5V V SYNC = 0V V IN = 12V V OUT = 5V I LOAD = 1A INPUT VOL TAGE (V) –0.15 –0.12 –0.09 –0.06 –0.03 0.03 0.06 0.09 0.12 0.15 CHANGE IN V OUT (%)

8636 G16

V OUT = 5V L = 4.7µH IN REGULATION INPUT VOL TAGE (V) 100 125 150 175 200 225 INPUT CURRENT (µA)

8636 G18

LT8637 Line Regulation LT8637 No-Load Supply Current

Rev. CFor more information www.analog.com TYPICAL PERFORMANCE CHARACTERISTICS Dropout Voltage Switching Frequency Burst Frequency LT8636 Soft-Start T racking Minimum On-TimeSwitch Drop vs Switch Current Top FET Current Limit vs Duty Cycle Top FET Current Limit Switch Drop vs Temperature DUTY CYCLE 0.1 0.3 0.5 0.7 0.9 6.0 6.5 7.0 7.5 8.0 8.5 9.0 9.5 10.0 10.5 11.0 CURRENT LIMIT (A)

8636 G19

5% DC TEMPERATURE (°C) –50 –25 100 125 150 CURRENT LIMIT (A) Top FET Current Limit

8636 G20

SWITCH CURRENT = 1A TEMPERATURE (°C) –50 –25 100 125 100 125 150 SWITCH DROP (mV)

8636 G21

SWITCH CURRENT (A) 100 150 200 250 300 350 400 450 500 SWITCH DROP (mV)

8636 G22

V IN = 5V V OUT SET TO REGULATE AT 5V L = IHLP3232DZ-01, 1µH LOAD CURRENT (A) 0.5 1.5 2.5 3.5 4.5 100 200 300 400 500 600 DROPOUT VOL TAGE (mV)

8636 G23

I LOAD = 2A V fSW = 3MHz OUT = 0.97V Burst Mode OPERATION FORCED CONTINUOUS MODE TEMPERATURE (°C) –50 –25 100 125 MINIMUM ON–TIME (ns)

8636 G24

R T = 60.4k TEMPERATURE (°C) –50 –25 100 125 150 660 670 680 690 700 710 720 730 740 SWITCHING FREQUENCY (kHz) Switching Frequency

8636 G25

V IN = 12V V OUT = 5V LOAD CURRENT (mA) 100 200 300 400 500 600 200 400 600 800 1000 1200 SWITCHING FREQUENCY (kHz)

8636 G26

TR/SS VOLTAGE (V) FB VOLTAGE (V) 0.8 1.0 1.2 0.6 1.0

8636 G27

0.6 0.4 0.2

Rev. C For more information www.analog.com Soft-Start Current PG High Thresholds PG Low Thresholds TYPICAL PERFORMANCE CHARACTERISTICS RT Programmed Switching Frequency Minimum Input Voltage Bias Pin Current V SS = 0.5V TEMPERATURE (°C) –50 –25 100 125 150 1.4 1.5 1.6 1.7 1.8 1.9 2.0 2.1 2.2 SS PIN CURRENT (µA) Soft–Start Current

8636 G29

TEMPERATURE (°C) –50 –25 100 125 150 6.0 6.5 7.0 7.5 8.0 8.5 9.0 9.5 10.0 PG THRESHOLD OFFSET FROM V REF (%) PG High Thresholds

8636 G31

TEMPERATURE (°C) –50 –25 100 125 150 –10.0 –9.5 –9.0 –8.5 –8.0 –7.5 –7.0 –6.5 –6.0 PG THRESHOLD OFFSET FROM V REF (%) PG Low Thresholds

8636 G32

SWITCHING FREQUENCY (MHz) 0.2 RT PIN RESISTOR (k/uni03A9) 150 200 250 1.8

8636 G33

0.6 1 1.4 2.2 2.6 3 TEMPERATURE (°C) –50 –25 100 125 2.4 2.6 2.8 3.0 3.2 3.4 3.6 INPUT VOL TAGE (V) Minimum Input Voltage

8636 G34

V BIAS = 5V V OUT = 5V I LOAD = 1A f SW = 1MHz INPUT VOL TAGE (V) 5.5 6.0 6.5 7.0 7.5 8.0 8.5 BIAS PIN CURRENT (mA)

8636 G35

V BIAS = 5V V OUT = 5V V IN = 12V I LOAD = 1A SWITCHING FREQUENCY (MHz) 0.2 0.6 1.4 1.8 2.2 2.6 3.0 BIAS PIN CURRENT (mA) Bias Pin Current

8636 G36

TR/SS VOL TAGE (V) 0.2 0.4 0.6 0.8 1.2 1.4 1.6 0.2 0.4 0.6 0.8 1.0 1.2 FB VOL TAGE (V)

8636 G28

V C = 1.25V FB PIN ERROR VOL TAGE (mV) –200 –100 100 200 –500 –375 –250 –125 125 250 375 500 V C PIN CURRENT (µA)

8636 G30

LT8637 Error Amp Output CurrentLT8637 Soft-Start T racking

Rev. CFor more information www.analog.com TYPICAL PERFORMANCE CHARACTERISTICS Case Temperature Rise Case Temperature Rise vs 7A Pulsed Load DEMO BOARD IN STILL AIR L = XEL6030, 1.5µH V IN = 12V , f SW = 1MHz V IN = 24V , f SW = 1MHz V IN = 12V , f SW = 2MHz V IN = 24V , f SW = 2MHz LOAD CURRENT (A) CASE TEMPERATURE RISE (°C)

8636 G37

V IN = 12V V OUT = 5V f SW = 2MHz STANDBY LOAD = 0.25A 1kHz PULSED LOAD = 7A DUTY CYCLE OF 7A LOAD 0.2 0.4 0.6 0.8 105 120 135 CASE TEMPERATURE RISE (°C)

8636 G38

V IN = 12V I LOAD = 2A 2ns/DIV V SW 2V/DIV

8636 G39

Switching Waveforms, Full Frequency Continuous Operation Switching Waveforms, Burst Mode Operation Switching Rising Edge FRONT PAGE APPLICATION 12V IN TO 5V OUT AT 1A 500ns/DIV I L 1A/DIV V SW 5V/DIV

8636 G40

V SYNC = 0V 5µs/DIV V SW 5V/DIV I L 500mA/DIV

8636 G41

V SW 10V/DIV I L 1A/DIV

8636 G42

LT8636 T ransient Response; Internal Compensation 2A TO 4A TRANSIENT 12V IN , 5V OUT FRONT PAGE APPLICATION f SW = 2MHz C OUT = 100µF , C LEAD = 10pF 20µs/DIV V OUT 100mV/DIV I LOAD 2A/DIV

8636 G43

, 5V OUT f SW = 2MHz C C = 330pF , R C = 8.45k C OUT = 100µF , C LEAD = 4.7pF 20µs/DIV V OUT 100mV/DIV I LOAD 2A/DIV

8636 G44

LT8637 T ransient Response; External Compensation

Rev. C For more information www.analog.com TYPICAL PERFORMANCE CHARACTERISTICS LT8636 T ransient Response; 100mA to 1.1A T ransient FRONT PAGE APPLICATION 100mA TO 1.1A TRANSIENT C OUT = 100µF Burst Mode OPERATION FCM 50µs/DIV I LOAD 1A/DIV V OUT 100mV/DIV

8636 G45

, 5V OUT , f SW = 1MHz Start-Up Dropout Performance Start-Up Dropout Performance VIN 2V/DIV VOUT 2V/DIV 100ms/DIV 2.5/uni03A9 LOAD (2A IN REGULATION)

8636 G47

(250mA IN REGULATION)

8636 G48

C C = 330pF , R C = 6.49k, C LEAD = 4.7pF 100mA TO 1.1A TRANSIENT 12V IN , 5V OUT , f SW = 1MHz C OUT = 100µF Burst Mode OPERATION FCM 50µs/DIV I LOAD 1A/DIV V OUT 100mV/DIV

8636 G46

LT8637 T ransient Response; 100mA to 1.1A T ransient

Rev. CFor more information www.analog.com Radiated EMI Performance (CISPR25 Radiated Emission Test with Class 5 Peak Limits) Conducted EMI Performance TYPICAL PERFORMANCE CHARACTERISTICS VERTICAL POLARIZATION PEAK DETECTOR DC2918A DEMO BOARD (WITH EMI FIL TER INSTALLED) 14V INPUT TO 5V OUTPUT AT 5A, f SW = 2MHz CLASS 5 PEAK LIMIT SPREAD SPECTRUM MODE FIXED FREQUENCY MODE FREQUENCY (MHz) 100 200 300 400 500 600 700 800 900 1000 AMPLITUDE (dBµV/m) (CISPR25 Radiated Emission Test with Class 5 Peak Limits) Radiated EMI Performance

8636 G50

(WITH EMI FIL TER INSTALLED) 14V INPUT TO 5V OUTPUT AT 5A, f SW = 2MHz SPREAD SPECTRUM MODE FIXED FREQUENCY MODE FREQUENCY (MHz) –40 –30 –20 –10 AMPLITUDE (dBµV/m) Conducted EMI Performance

8636 G49

Rev. C For more information www.analog.com 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, V IN 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. INTV CC 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 V IN. 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. 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 V IN 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 VIN bypass capacitors. T wo small 1µF capaci- tors should be placed as close as possible to the LT8636/ LT8637, one capacitor on each side of the device (C IN1, CIN2). A third capacitor with a larger value, 2.2µF or higher , should be placed near C IN1 or C IN2. 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 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. 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 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 <1µA. See Block Diagram for internal pull-up and pull-down resistance. 3) Spread spectrum mode. Tie this pin high to INTV CC (~3.4V) or an external supply 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. 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. RT (Pin 17): A resistor is tied between RT and ground to set the switching frequency.

Rev. CFor more information www.analog.com TR/SS (Pin 18): Output T racking 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 amplifier . An internal 1.9µA pull-up current from INTVCC on this pin allows a capacitor to program output voltage slew rate. This pin is pulled to ground with an internal 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. 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 VOUT. Typically, this capacitor is 4.7pF to 22pF. VC (Pin 19, LT8637 Only): The VC pin is the output of the 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 VOUT. Typically, this capacitor is 4.7pF to 22pF. Corner Pins: These pins are for mechanical support only and can be tied anywhere on the PCB, typically ground. PIN FUNCTIONS

Rev. C For more information www.analog.com BLOCK DIAGRAM 8636 BD ++– SLOPE COMP INTERNAL 0.97V REF OSCILLATOR 200kHz TO 3MHz BURST DETECT 3.4V REG CBST COUT VOUT SW 8–10 L BST SWITCH LOGIC AND ANTI-SHOOT THROUGH ERROR AMP SHDN ±8% VC SHDN THERMAL SHDN INTVCC UVLO VIN UVLO SHDN THERMAL SHDN VIN UVLO EN/UV 1V + –14 INTVCC BIAS 2 VIN GND 4, 13, 21 CLKOUT PG VC FB R1C1 OPT RC CC OPT RT CSS OPT VOUT TR/SS 1.9µA RT17 SYNC/MODE15 VINVIN CIN1 CF CIN3 CIN2 CVCC INTVCC 60k 600k L T8636 ONL Y L T8637 ONL Y

Rev. CFor more information www.analog.com 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 by comparing the voltage on the V FB pin with an inter - 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. 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. 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 = 5VOUT) will be consumed from the input supply when regulating 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. 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 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. To improve efficiency across all loads, supply current to internal circuitry can be sourced from the BIAS pin when biased at 3.3V or above. Else, the internal circuitry will draw current from VIN. The BIAS pin should be connected to VOUT if the LT8636/LT8637 output is programmed at 3.3V to 25V. The V C 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. 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.

Figure 1. Recommended PCB Layouts for the LT8636 See Figure 1 for recommended PCB layouts. Board guide for the LT8636/LT8637. 0603 are optimal due to lowest parasitic inductance. application circuit on the layer closest to the surface layer . The SW and BOOST nodes should be as small as possible. traces will shield them from the SW and BOOST nodes.

Typical Performance Characteristics. Figure 2. SW Frequency vs Load Information Figure 3. Burst Mode Operation

8636 F02

8636 F03

and the LT8636/LT8637 operates in pulse-skipping mode.

• 1– VOUT VIN,MAX 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 INTVCC (~3.4V)or an external supply of 3V to 4V. 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. Synchronization 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. 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). Forced Continuous Mode 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.

Figure 4. LT8636 Load Step T ransient Response with

8636 F04

500kHz and higher , the RT should be selected for 500kHz. 1M and R2 = 412k, the feedback divider draws 2.3µA. Typical Performance Characteristics section. capacitor should be connected from VOUT to FB. desired switching frequency is in Table 1. Table 1. SW Frequency vs RT Value

Rev. C For more information www.analog.com APPLICATIONS INFORMATION Operating Frequency Selection and T rade-Offs Selection of the operating frequency is a trade-off between efficiency, component size, and input voltage range. The advantage of high frequency operation is that smaller inductor and capacitor values may be used. The disadvan- tages are lower efficiency and a smaller input voltage range. The highest switching frequency (f SW(MAX)) for a given application can be calculated as follows: fSW(MAX) = VOUT + VSW(BOT) tON(MIN) VIN – VSW(TOP) + VSW(BOT)( ) (4) where VIN is the typical input voltage, VOUT is the output voltage, VSW(TOP) and V SW(BOT) are the internal switch drops (~ 0.4V, ~0.15V, respectively at maximum load) and tON(MIN) is the minimum top switch on-time (see the Electrical Characteristics). This equation shows that a slower switching frequency is necessary to accommodate a high VIN/VOUT ratio. For transient operation, VIN may go as high as the abso- lute maximum rating of 42V regardless of the R T value, however the LT8636/ LT8637 will reduce switching fre - quency as necessary to maintain control of inductor cur- rent to assure safe operation. The LT8636/LT8637 is capable of a maximum duty cycle of approximately 99%, and the V IN-to-VOUT dropout is limited by the RDS(ON) of the top switch. In this mode the LT8636/LT8637 skips switch cycles, resulting in a lower switching frequency than programmed by RT . For applications that cannot allow deviation from the pro- grammed switching frequency at low VIN/VOUT ratios use the following formula to set switching frequency: VIN(MIN) = VOUT + VSW(BOT) 1– fSW •tOFF(MIN) – VSW(BOT) + VSW(TOP) (5) where V IN(MIN) is the minimum input voltage without skipped cycles, VOUT is the output voltage, VSW(TOP) and VSW(BOT) are the internal switch drops (~ 0.4V, ~0.15V, respectively at maximum load), f SW is the switching frequency (set by R T), and t OFF(MIN) is the minimum switch off-time. Note that higher switching frequency will increase the minimum input voltage below which cycles will be dropped to achieve higher duty cycle. Inductor Selection and Maximum Output Current The 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. A good first choice for the inductor value is: L = VOUT + VSW(BOT) fSW ⎠⎟•0.7 (6) where fSW is the switching frequency in MHz, V OUT is the output voltage, V SW(BOT) is the bottom switch drop (~0.15V) and L is the inductor value in µH. To avoid overheating and poor efficiency, an inductor must be chosen with an RMS current rating that is greater than the maximum expected output load of the application. In addition, the saturation current (typically labeled ISAT) rating of the inductor must be higher than the load current plus 1/2 of in inductor ripple current: IL(PEAK) =ILOAD(MAX) + 1 2 ΔIL (7) where ∆IL is the inductor ripple current as calculated in Equation 9 and I LOAD(MAX) is the maximum output load for a given application. As a quick example, an application requiring 3A output should use an inductor with an RMS rating of greater than 3A and an ISAT of greater than 4A. During long duration overload or short-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. The LT8636/LT8637 limits the peak switch current in order to protect the switches and the system from over- load faults. The top switch current limit (I LIM) is 10A at low duty cycles and decreases linearly to 7A at DC = 0.8. The inductor value must then be sufficient to supply the desired maximum output current (IOUT(MAX)), which is a function of the switch current limit (I LIM) and the ripple current.

Rev. CFor more information www.analog.com APPLICATIONS INFORMATION IOUT(MAX) =ILIM – ΔIL (8) The peak-to-peak ripple current in the inductor can be calculated as follows: ΔIL = VOUT L •fSW

• 1– VOUT VIN(MAX) (9) where f SW 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 (IOUT(MAX)) given the switching frequency, and maximum input voltage used in the desired application. 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. 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. For more information about maximum output current and discontinuous operation, see Analog Devices Application Note 44. For duty cycles greater than 50% (V OUT/VIN > 0.5), a minimum inductance is required to avoid subharmonic oscillation (See Equation 10). See Application Note 19 for more details. LMIN = VIN 2 •DC – 1( ) 3.5 • fSW (10) where DC is the duty cycle ratio (VOUT/VIN) and fSW is the switching frequency. Input Capacitors The VIN of the LT8636/LT8637 should be bypassed with at least three ceramic capacitors for best performance. T wo 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/ LT8637 near the VIN and GND pins. A third, larger ceramic capacitor of 2.2µF or larger should be placed close to C IN1 or C IN2. See layout section for 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 . 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 For more information www.analog.com APPLICATIONS INFORMATION Output Capacitor and Output Ripple 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. Use X5R or X7R types. This choice will provide low out- put ripple and good transient response. T ransient perfor- mance can be improved with a higher value output capaci- tor and the addition of a feedforward capacitor placed between VOUT and FB. Increasing the output capacitance will also decrease the output voltage ripple. A lower value of output capacitor can be used to save space and cost but transient performance will suffer and may cause loop instability. See the Typical Applications in this data sheet for suggested capacitor values. When choosing a capacitor , special attention should be given to the data sheet to calculate the effective 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. Ceramic Capacitors 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. 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). 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 IN if the shutdown feature is not used, or tied to a logic level if shutdown control is required. Adding a resistor divider from V IN to EN programs the LT8636/LT8637 to regulate the output only when V IN is above a desired voltage (see the Block Diagram). Typically, this threshold, V IN(EN), is used in situations where the input supply is current limited, or has a relatively high source resistance. A switching regulator draws constant power from the source, so source current increases as source voltage drops. This looks like a negative resistance load to the source and can cause the source to current limit or latch low under low source voltage conditions. The VIN(EN) threshold prevents the regulator from operating at source voltages where the problems might occur . This threshold can be adjusted by setting the values R3 and R4 such that they satisfy the following equation: VIN(EN) = R3 R4 +1⎛ ⎝⎜ ⎞ ⎠⎟•1.0V (11) where the LT8636/ LT8637 will remain off until V IN is above VIN(EN). Due to the comparator’s hysteresis, switch- 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 V IN(EN) resistors should be large to minimize their effect on efficiency at low loads.

an external load to the INTVCC pin. how to test the stability using a transient load. output current proportional to the voltage at the V C pin. amplifier output current, resulting in two poles in the loop.

8636 F05

Figure 5. Model for Loop Response

voltage will regulate to the internal reference voltage. be left floating if the function is not needed. falling too low, or thermal shutdown. get one output capable of up to 10A. Figure 6. Paralleling T wo LT8637s

8636 F06

low, VIN is too low, or thermal shutdown. slow switching if the inductor current exceeds safe levels. a shorted or reversed input. Figure 7. Reverse VIN Protection

8636 F07

resistance from junction to ambient. condition until the temperature drops about 10°C cooler . ating at high load, high VIN, and high switching frequency. decreased to reduce the temperature to an acceptable level. be managed by reducing VIN, switching frequency, or load. ble of safely delivering up to 7A of peak output current. Figure 8. Case Temperature Rise Figure 9. Case Temperature Rise vs 7A Pulsed Load

8636 F08

8636 F09

Typical Performance Characteristics.

Figure 10. 5V, 5A Step-Down Converter with Soft-Start and Power Good Figure 11. 3.3V, 5A Step-Down Converter with Soft-Start and Power Good

8636 F10

8636 F11

• VC pin and components only apply to L T8637.

Figure 13. 2MHz 5V, 5A Step-Down Converter with Spread Spectrum

8636 F13

Figure 12. Ultralow EMI 5V, 5A Step-Down Converter with Spread Spectrum

8636 F12

• VC pin and components only apply to L T8637.

Figure 14. 2MHz 3.3V, 5A Step-Down Converter with Spread Spectrum Figure 15. 12V, 5A Step-Down Converter

8636 F15

8636 F14

• VC pin and components only apply to L T8637.

Rev. C For more information www.analog.com PACKAGE DESCRIPTION 20-Lead (4mm × 3mm × 0.94mm) (Reference L TC DWG # 05-08-1602 Rev A) PACKAGE TOP VIEW PIN 1 CORNER Y X aaa Z2× 20b PACKAGE BOTTOM VIEW

6 SEE NOTES

E D b e e b DETAIL B SUBSTRATE MOLD CAP // bbb Z Z DETAIL A DETAIL C SUGGESTED PCB LAYOUT TOP VIEW 0.0000 0.0000 0.7500 1.2500 0.2500 0.2500 0.7500 1.2500 0.7500 0.2500 0.2500 0.7500 DETAIL A PIN 1 NOTCH 0.25 × 45° 17 20 0.375 0.375 aaa Z 2× M X YZccc MXY Z ccc M X YZeee M Zfff PACKAGE OUTLINE 0.25 ±0.05 0.70 ±0.05 0.375 0.375 4.50 ±0.05 3.50 ±0.05 0.275 2.65 1.65 ddd Z 20× e SYMBOL A L b D E e aaa bbb ccc ddd eee fff MIN 0.85 0.01 0.30 0.22 NOM 0.94 0.02 0.40 0.25 3.00 4.00 1.65 2.65 0.50

0.24 REF

0.70 REF

1.03 0.03 0.50 0.28 0.10 0.10 0.10 0.10 0.15 0.08 NOTES DIMENSIONS Z DETAIL C NOTES: 1. DIMENSIONING AND TOLERANCING PER ASME Y14.5M-1994 2. ALL DIMENSIONS ARE IN MILLIMETERS 3. PRIMARY DATUM -Z- IS SEATING PLANE METAL FEATURES UNDER THE SOLDER MASK OPENING NOT SHOWN SO AS NOT TO OBSCURE THESE TERMINALS AND HEAT FEATURES DETAILS OF PIN 1 IDENTIFIER ARE OPTIONAL, BUT MUST BE LOCATED WITHIN THE ZONE INDICATED. THE PIN 1 IDENTIFIER MAY BE EITHER A MOLD OR MARKED FEATURE

6 THE EXPOSED HEAT FEATURE MAY HAVE OPTIONAL CORNER RADII

7 CORNER SUPPORT PAD CHAMFER IS OPTIONAL

L e/2 DETAIL B A LQFN 20 0619 REV A PACKAGE IN TRAY LOADING ORIENTATION TRAY PIN 1 BEVEL COMPONENT PIN 1 L TXXXXXX NOTES SUBSTRATE THK MOLD CAP HT

Rev. CFor more information www.analog.com 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 is granted by implication or otherwise under any patent or patent rights of Analog Devices.

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 T ransient Output Replace T racking with Power Good Added AEC-Q100 Quaified for Automotive Applications Clarified GND pin numbers in Pin Functions Clarified Equations 7, 8, 9 16-17 B 04/20 Added LT8636JV#WTRPBF to the Order Information Table 2 C 12/20 Added LT8637 Added 8636MP All 2, 4

Rev. C For more information www.analog.com RELATED PARTS TYPICAL APPLICATIONS 2MHz 1.8V, 5A Step-Down Converter 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 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, MSOP-16E LT8610AC 42V, 3.5A, 96% 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-16E LT8610 42V, 2.5A, 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 = 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 Step- Down 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 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 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 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 VIN2VIN1 EN/UV L T8636

8636 TA02

PINS NOT USED IN THIS CIRCUIT : CLKOUT , PG, SYNC/MODE TR/SS SW BIAS INTVCC FB RT GND 0.1µF 1µF 10pF EXTERNAL SOURCE >3.1V OR GND 100µF 1210 X5R/X7R 10nF 866k VOUT 1.8V 1µF 0603 1µF 0603 4.7µF VIN 3.4V TO 22V (42V TRANSIENT) 17.8k 1µF 1µH GND2GND1 fSW = 2MHz L: XEL6030 www.analog.com  ANALOG DEVICES, INC. 2020