LT8610AB

LT8645S_V01 AD | Alldatasheet

Document overview

• Manufacturer or author: Analog Devices, Inc.
• PDF pages: 30

Technical content

Rev. BFor more information www.analog.comDocument Feedback TYPICAL APPLICATION FEATURES DESCRIPTION 65V, 8A Synchronous Step-Down Silent Switcher 2 with 2.5µA Quiescent Current The LT®8645S/LT8646S synchronous step-down regulator features second generation Silent Switcher architecture designed to minimize EMI emissions while delivering high efficiency at high switching frequencies. This includes the integration of bypass capacitors to optimize all the fast current loops inside and make it easy to achieve advertised EMI performance by eliminating layout sensitivity. The fast, clean, low-overshoot switching edges enable high efficiency operation even at high switching frequen- cies, leading to a small overall solution size. Peak current mode control with a 40ns minimum on-time allows high step-down ratios even at high switching frequencies. The LT8646 S has external compensation to enable current sharing and fast transient response at high switching frequencies. Burst Mode ® operation enables ultralow standby current consumption, pulse-skipping mode allows full switching frequency at lower output loads, or spread spectrum operation can further reduce EMI emissions. INTERNAL CAPS V C COMP 150°C GRADE LT8645S Yes Internal No LT8646S Yes External No LT8645S-2* No Internal Yes *See LT8645S-2 Data Sheet 5V 8A Step-Down Converter

APPLICATIONS

n Silent Switcher®2 Architecture n Ultralow EMI Emissions on Any PCB n Eliminates PCB Layout Sensitivity n Internal Bypass Capacitors Reduce Radiated EMI n Optional Spread Spectrum Modulation n High Efficiency at High Frequency n Up to 95% Efficiency at 1MHz, 12VIN to 5VOUT n Up to 94% Efficiency at 2MHz, 12VIN to 5VOUT n Wide Input Voltage Range: 3.4V to 65V n Ultralow Quiescent Current Burst Mode Operation n 2.5μA IQ Regulating 12VIN to 3.3VOUT (LT8645S) n Output Ripple < 10mVP-P n External Compensation: Fast T ransient Response and Current Sharing (LT8646S) n Fast Minimum Switch On-Time: 40ns n Low Dropout Under All Conditions: 60mV at 1A n Adjustable and Synchronizable: 200kHz to 2.2MHz n Peak Current Mode Operation n Output Soft-Start and T racking n Small 32-Lead 6mm × 4mm LQFN Package n AEC-Q100 Qualified for Automotive Applications n Automotive and Industrial Supplies n General Purpose Step-Down n GSM Power Supplies All registered trademarks and trademarks are the property of their respective owners. Protected by U.S. patents, including 8823345. 12VIN to 5VOUT Efficiency L T8645S 8645S TA01a SW BIAS FB V IN 5.5V TO 65V GND RT V IN EN/UV V OUT 100µF 2.2pF 4.7µF 41.2k 243k 2.2µH f SW = 1MHz EFFICIENCY POWER LOSS 1MHz, L = 2.2µH 2MHz, L = 1µH LOAD CURRENT (A) 100 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 EFFICIENCY (%) POWER LOSS (W) 8645S TA01b

Rev. B For more information www.analog.com PIN CONFIGURATION ABSOLUTE MAXIMUM RATINGS B V S (Note 1) LT8645S LT8646S LQFN PACKAGE 32-LEAD (6mm × 4mm × 0.94mm) JEDEC BOARD: θJA = 30°C/W , ΨJT = 0.6°C/W , θJCTOP = 28.5°C/W , θJC(PAD) = 4.4°C/W (NOTE 3) DEMO BOARD: θJA = 17°C/W EXPOSED PADS (PINS 33-38) ARE GND, SHOULD BE SOLDERED TO PCB TOP VIEW 11 12 13 14 15 16 32 31 30 29 28 27 V IN GND GND GND NC BIAS V IN VIN NC INTVCC VIN GND GND GND NC RT V IN VIN NC EN/UV33 GND GND GND GND GND GND BST SW SW SW SW SW FB PG GND TR/SS SYNC/MODE CLKOUT LQFN PACKAGE 32-LEAD (6mm × 4mm × 0.94mm) JEDEC BOARD: θJA = 30°C/W , ΨJT = 0.6°C/W , θJCTOP = 28.5°C/W , θJC(PAD) = 4.4°C/W (NOTE 3) DEMO BOARD: θJA = 17°C/W EXPOSED PADS (PINS 33-38) ARE GND, SHOULD BE SOLDERED TO PCB TOP VIEW 11 12 13 14 15 16 32 31 30 29 28 27 V IN GND GND GND NC BIAS V IN VIN NC INTVCC VIN GND GND GND NC RT V IN VIN NC EN/UV33 GND GND GND GND GND GND BST SW SW SW SW SW FB PG V C TR/SS SYNC/MODE CLKOUT Operating Junction Temperature Range (Note 2) LT 125°C LT C to 150°C Maximum Reflow (Package Body) Temperature ...26 0°C

Rev. BFor more information www.analog.com ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. ORDER INFORMATION PARAMETER CONDITIONS MIN TYP MAX UNITS Minimum Input Voltage l 3.0 3.4 V VIN Quiescent Current in Shutdown V EN/UV = 0V l 0.9 0.9 µA µA LT8645S V IN Quiescent Current in Sleep (Internal Compensation) VEN/UV = 2V, VFB > 0.97V, VSYNC = 0V l 1.7 1.7 µA µA LT8646S V IN Quiescent Current in Sleep (External Compensation) VEN/UV = 2V, VFB > 0.97V, VSYNC = 0V, VBIAS = 0V l 230 230 290 340 µA µA V EN/UV = 2V, VFB > 0.97V, VSYNC = 0V, VBIAS = 5V 16 25 µA LT8646S BIAS Quiescent Current in Sleep V EN/UV = 2V, VFB > 0.97V, VSYNC = 0V, VBIAS = 5V 200 260 µA LT8645S VIN Quiescent Current when Active V EN/UV = 2V, VFB > 0.97V, VSYNC = 2V, RT = 60.4k, VBIAS = 0V 0.4 0.6 mA LT8646S VIN Quiescent Current when Active V EN/UV = 2V, VFB > 0.97V, VSYNC = 2V, RT = 60.4k, VBIAS = 0V 0.6 0.8 mA LT8645S VIN Current in Regulation V OUT = 0.97V, VIN = 6V, ILOAD = 100µA, VSYNC = 0V VOUT = 0.97V, VIN = 6V, ILOAD = 1mA, VSYNC = 0V l l 200 400 µA µA Feedback Reference Voltage VIN = 6V VIN = 6V l 0.964 0.958 0.970 0.970 0.976 0.982 V V Feedback Voltage Line Regulation V IN = 4.0V to 42V l 0.004 0.025 %/V Feedback Pin Input Current VFB = 1V –20 20 nA LT8646S Error Amp T ransconductance V C = 1.25V 1.7 mS LT8646S Error Amp Gain 350 V/V LT8646S VC Source Current VFB = 0.77V, VC = 1.25V 350 µA LT8646S VC Sink Current VFB = 1.17V, VC = 1.25V 350 µA PART NUMBER PART MARKING* FINISH CODE PAD FINISH PACKAGE TYPE* MSL RATING TEMPERATURE RANGE LT8645SEV#PBF 8645SV e4 Au (RoHS) LQFN (Laminate Package with QFN Footprint) 3 –40°C to 125°CLT8645SIV#PBF LT8646SEV#PBF 8646SVLT8646SIV#PBF AUTOMOTIVE PRODUCTS LT8645SEV#WPBF 8645SV e4 Au (RoHS) LQFN (Laminate Package with QFN Footprint) 3 –40°C to 125°CLT8645SIV#WPBF LT8646SEV#WPBF 8646SVLT8646SIV#WPBF Contact the factory for parts specified with wider operating temperature ranges. *Pad or ball finish code is per IPC/JEDEC J-STD-609.

• Recommended LGA and BGA PCB Assembly and Manufacturing Procedures
• LGA and BGA Package and Tray Drawings Parts ending with PBF are RoHS and WEEE compliant. *The LT8645S/LT8646 S package has the same footprint as a standard 6mm × 4mm 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 For more information www.analog.com PARAMETER CONDITIONS MIN TYP MAX UNITS LT8646S VC Pin to Switch Current Gain 8 A/V LT8646S VC Clamp Voltage 2.6 V BIAS Pin Current Consumption VBIAS = 3.3V, fSW = 2MHz 22 mA Minimum On-Time ILOAD = 2A, SYNC = 0V ILOAD = 2A, 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 I SW = 1A 36 mΩ Top Power NMOS Current Limit l 10.5 14 17.5 A Bottom Power NMOS On-Resistance V INTVCC = 3.4V, ISW = 1A 25 mΩ Bottom Power NMOS Current Limit V INTVCC = 3.4V 8.5 11 13.5 A SW Leakage Current VIN = 42V, VSW = 0V, 42V –1.5 1.5 µA EN/UV Pin Threshold EN/UV Rising l 0.95 1.01 1.07 V EN/UV Pin Hysteresis 45 mV EN/UV Pin Current VEN/UV = 2V –20 20 nA PG Upper Threshold Offset from VFB VFB Falling l 5 7.5 10 % PG Lower Threshold Offset from VFB VFB Rising l –10.5 –8 –5.5 % PG Hysteresis 0.4 % PG Leakage VPG = 3.3V –40 40 nA PG Pull-Down Resistance VPG = 0.1V l 750 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 R T = 60.4k, VSYNC = 3.3V 24 % Spread Spectrum Modulation Frequency V SYNC = 3.3V 2.5 kHz TR/SS Source Current l 1.2 1.9 2.6 µA TR/SS Pull-Down Resistance Fault Condition, TR/SS = 0.1V 220 Ω 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 LT8645SE/LT8646SE 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 LT8645SI/LT8646SI is guaranteed over the full –40°C to 125°C operating junction temperature range. The junction temperature (T J, 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 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. ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C.

Rev. BFor more information www.analog.com TYPICAL PERFORMANCE CHARACTERISTICS 12VIN to 5VOUT Efficiency vs Frequency 12VIN to 3.3VOUT Efficiency vs Frequency Efficiency at 5VOUT Efficiency at 3.3VOUT LT8645S Low Load Efficiency at 5VOUT LT8645S Low Load Efficiency at 3.3V OUT Efficiency vs Frequency LT8646S Low Load Efficiency at 5V OUT LT8646S Low Load Efficiency at 3.3V OUT EFFICIENCY POWER LOSS L = XEL6060 500kHz, L = 2.7µH 1MHz, L = 2.2µH 2MHz, L = 1µH LOAD CURRENT (A) 100 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 EFFICIENCY (%) POWER LOSS (W) 8645S G01 EFFICIENCY POWER LOSS L = XEL6060 500kHz, L = 2.7µH 1MHz, L = 1.5µH 2MHz, L = 0.82µH LOAD CURRENT (A) 100 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 EFFICIENCY (%) POWER LOSS (W) 8645S G02 f SW = 500kHz L = XEL6060, 2.7µH EFFICIENCY POWER LOSS V IN = 12V V IN = 24V V IN = 36V V IN = 48V LOAD CURRENT (A) 100 0.4 0.8 1.2 1.6 2.0 2.4 2.8 3.2 3.6 4.0 EFFICIENCY (%) POWER LOSS (W) 8645S G03 f SW = 500kHz L = XEL6060, 2.7µH EFFICIENCY POWER LOSS V IN = 12V V IN = 24V V IN = 36V V IN = 48V LOAD CURRENT (A) 100 0.4 0.8 1.2 1.6 2.0 2.4 2.8 3.2 3.6 4.0 EFFICIENCY (%) POWER LOSS (W) 8645S G04 V OUT = 3.3V I LOAD = 2A L = XEL6060, 4.7µH V IN = 12V V IN = 24V SWITCHING FREQUENCY (MHz) 0.4 0.7 1.3 1.6 1.9 2.2 EFFICIENCY (%) 8645S G09 f SW = 500kHz L = WE–LHMI7050, 4.7µH V IN = 12V V IN = 24V V IN = 36V V IN = 48V LOAD CURRENT (mA) 0.01 0.1 100 1000 100 EFFICIENCY (%) 8645S G05 f SW = 500kHz L = WE–LHMI7050, 4.7µH V IN = 12V V IN = 24V V IN = 36V V IN = 48V LOAD CURRENT (mA) 0.1 100 1000 100 EFFICIENCY (%) OUT 8645S G06 f SW = 500kHz L = WE–LHMI7050, 4.7µH V IN = 12V V IN = 24V V IN = 36V V IN = 48V LOAD CURRENT (mA) 0.01 0.1 100 1000 100 EFFICIENCY (%) 8645S G07 f SW = 500kHz L = WE–LHMI7050, 4.7µH V IN = 12V V IN = 24V V IN = 36V V IN = 48V LOAD CURRENT (mA) 0.1 100 1000 100 EFFICIENCY (%) L T8646S Low Load Efficiency at 3.3V OUT 8645S G08

Rev. B For more information www.analog.com TYPICAL PERFORMANCE CHARACTERISTICS EN Pin ThresholdsReference Voltage LT8645S Load Regulation LT8645S Line Regulation LT8645S No-Load Supply Current Burst Mode Operation Efficiency vs Inductor Value (LT8645S) LT8646S Load Regulation LT8646S Line Regulation LT8646S No-Load Supply Current V OUT = 5V I LOAD = 10mA L = WE–LHMI7050 V IN = 12V V IN = 24V INDUCTOR VALUE (µH) 100 EFFICIENCY (%) 8645S G10 TEMPERATURE (°C) –50 –25 100 125 961 963 965 967 969 971 973 975 977 979 REFERENCE VOL TAGE (mV) 8645S G11 EN RISING EN FALLING TEMPERATURE (°C) –50 –25 100 125 0.95 0.96 0.97 0.98 0.99 1.00 1.01 1.02 1.03 EN THRESHOLD (V) 8645S G12 LOAD CURRENT (A) –0.10 –0.05 0.05 0.10 0.15 0.20 CHANGE IN V OUT (%) 8645S G13 V OUT = 5V V IN = 12V V SYNC = 0V V OUT = 5V V IN = 12V V SYNC = 0V LOAD CURRENT (A) –0.50 –0.40 –0.30 –0.20 –0.10 0.00 0.10 0.20 0.30 0.40 CHANGE IN V OUT (%) 8645S G14 V OUT = 5V I LOAD = 2A INPUT VOL TAGE (V) –0.10 –0.05 0.00 0.05 0.10 0.15 0.20 CHANGE IN V OUT (%) 8645S G15 V OUT = 5V I LOAD = 2A INPUT VOL TAGE (V) –0.10 –0.05 0.05 0.10 0.15 0.20 0.25 0.30 CHANGE IN V OUT (%) L T8646S Line Regulation 8645S G16 V OUT = 5V L = 4.7µH IN REGULATION INPUT VOL TAGE (V) 100 125 150 175 200 225 INPUT CURRENT (µA) 8645S G18 V OUT = 3.3V L = 4.7µH IN-REGULATION INPUT VOL TAGE (V) 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 INPUT CURRENT (µA) 8645S G17

Rev. BFor more information www.analog.com Top FET Current Limit vs Duty Cycle Top FET Current Limit Switch Drop vs Temperature Switch Drop vs Switch Current TYPICAL PERFORMANCE CHARACTERISTICS Dropout Voltage Minimum On-Time Switching Frequency Burst Frequency Minimum Load to Full Frequency (Pulse-Skipping Mode) DUTY CYCLE 0.1 0.3 0.5 0.7 0.9 11.0 11.5 12.0 12.5 13.0 13.5 14.0 14.5 15.0 CURRENT LIMIT (A) 8645S G19 5% DC TEMPERATURE (°C) –50 –25 100 125 CURRENT LIMIT (A) 8645S G20 TOP SWITCH BOTTOM SWITCH SWITCH CURRENT = 1A TEMPERATURE (°C) –50 –25 100 125 100 SWITCH DROP (mV) 8645S G21 TOP SWITCH BOTTOM SWITCH SWITCH CURRENT (A) 100 150 200 250 300 350 SWITCH DROP (mV) 8645S G22 V IN = 5V V OUT SET TO REGULATE AT 5V L = XEL6060, 1µH LOAD CURRENT (A) 100 150 200 250 300 350 400 DROPOUT VOL TAGE (mV) 8645S G23 I LOAD = 3A V OUT = 0.97V f SW = 2.2MHz BURST MODE OPERATION PULSE–SKIPPING MODE TEMPERATURE (°C) –50 –25 100 125 MINIMUM ON-TIME (ns) 8645S G24 R T = 60.4k TEMPERATURE (°C) –50 –25 100 125 660 670 680 690 700 710 720 730 740 SWITCHING FREQUENCY (kHz) 8645S G25 FRONT PAGE APPLICATION V IN = 12V V OUT = 5V LOAD CURRENT (mA) 100 200 300 400 500 600 200 400 600 800 1000 1200 SWITCHING FREQUENCY (kHz) 8645S G26 FRONT PAGE APPLICATION V OUT = 5V f SW = 1MHz V SYNC = Float INPUT VOL TAGE (V) 100 150 200 250 300 350 400 LOAD CURRENT (mA) 8645S G27

Rev. B For more information www.analog.com TYPICAL PERFORMANCE CHARACTERISTICS Soft-Start Current PG High Thresholds PG Low Thresholds RT Programmed Switching Frequency Minimum Input Voltage Bias Pin Current LT8645S Soft-Start T racking LT8646S Soft-Start T racking LT8646S Error Amp Output Current TR/SS VOLTAGE (V) FB VOLTAGE (V) 0.8 1.0 1.2 0.6 1.0 8645S G28 0.6 0.4 0.2 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) L T8646S Soft-Start T racking 8645S G29 V SS = 0.5V TEMPERATURE (°C) –50 –25 100 125 1.4 1.5 1.6 1.7 1.8 1.9 2.0 2.1 2.2 TR/SS PIN CURRENT (µA) 8645S G30 V C = 1.25V FB PIN ERROR VOL TAGE (mV) –200 –100 100 200 –500 –375 –250 –125 125 250 375 500 V CC PIN CURRENT (µA) L T8646S Error Amp Output Current 8645S G31 FB RISING FB FALLING TEMPERATURE (°C) –50 –25 100 125 6.0 6.5 7.0 7.5 8.0 8.5 9.0 9.5 10.0 PG THRESHOLD OFFSET FROM V REF (%) 8645S G32 FB RISING FB FALLING TEMPERATURE (°C) –50 –25 100 125 –10.0 –9.5 –9.0 –8.5 –8.0 –7.5 –7.0 –6.5 –6.0 PG THRESHOLD OFFSET FROM V REF (%) 8645S G33 SWITCHING FREQUENCY (MHz) 0.2 RT PIN RESISTOR (k/uni03A9) 150 200 250 1.8 8645S G34 100 125 175 225 0.6 1 1.4 2.2 TEMPERATURE (°C) –50 –25 100 125 2.4 2.6 2.8 3.0 3.2 3.4 3.6 INPUT VOL TAGE (V) 8645S G35 V BIAS = 5V V OUT = 5V f SW = 1MHz INPUT VOL TAGE (V) BIAS PIN CURRENT (mA) 8645S G36

Rev. BFor more information www.analog.com TYPICAL PERFORMANCE CHARACTERISTICS Bias Pin Current Case Temperature Rise Switch Rising Edge Switching Waveforms, Full Frequency Continuous Operation Switching Waveforms, Burst Mode Operation Switching Waveforms 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 BIAS PIN CURRENT (mA) 8645S G37 DC2468A DEMO BOARD V IN = 12V , f SW = 500kHz V IN = 24V , f SW = 500kHz V IN = 12V , f SW = 2MHz V IN = 24V , f SW = 2MHz LOAD CURRENT (A) CASE TEMPERATURE RISE (°C) 8645S G38 V IN = 12V I LOAD = 3A 2ns/DIV V SW 2V/DIV 8645S G39 FRONT PAGE APPLICATION 12V IN TO 5V OUT AT 2A 500ns/DIV V SW 5V/DIV I L 1A/DIV 8645S G40 FRONT PAGE APPLICATION 12V IN TO 5V OUT AT 10mA V SYNC = 0V 10µs/DIV V SW 5V/DIV I L 500mA/DIV 8645S G41 FRONT PAGE APPLICATION 48V IN TO 5V OUT AT 2A 500ns/DIV V SW 20V/DIV I L 1A/DIV 8645S G42

Rev. B For more information www.analog.com TYPICAL PERFORMANCE CHARACTERISTICS Start-Up Dropout Performance Start-Up Dropout Performance LT8646S T ransient Response; 300mA (Burst Mode Operation) to 1.3A T ransient LT8645S T ransient Response; Internal Compensation LT8645S T ransient Response; 300mA (Burst Mode Operation) to 1.3A T ransient LT8646S T ransient Response; External Compensation Internal Compensation 2A TO 4A TRANSIENT 12V IN , 5V OUT , f SW = 2MHz C OUT = 100µF , C LEAD = 4.7pF 20µs/DIV V OUT 100mV/DIV I LOAD 2A/DIV 8645S G43 2A TO 4A TRANSIENT 12V IN , 5V OUT , f SW = 2MHz C C = 330pF , R C = 7.5k C OUT = 100µF , C LEAD = 4.7pF 20µs/DIV V OUT 100mV/DIV I LOAD 2A/DIV 8645S G44 to 1.3A T ransient 300mA TO 1.3A TRANSIENT 12V IN , 5V OUT , f SW = 2MHz C OUT = 100µF , C LEAD = 4.7pF 50µs/DIV V OUT 100mV/DIV I LOAD 1A/DIV 8645S G45 300mA TO 1.3A TRANSIENT 12V IN , 5V OUT , f SW = 2MHz C C = 330pF , R C = 7.5k C OUT = 100µF , C LEAD = 4.7pF 50µs/DIV V OUT 100mV/DIV I LOAD 1A/DIV 8645S G46 VIN 2V/DIV VOUT 2V/DIV 100ms/DIV 2.5/uni03A9 LOAD (2A IN REGULATION) 8645S G47 VIN VOUT VIN 2V/DIV VOUT 2V/DIV 100ms/DIV 20/uni03A9 LOAD (250mA IN REGULATION) 8645S G48 VIN VOUT

Rev. BFor more information www.analog.com Radiated EMI Performance (CISPR25 Radiated Emission Test with Class 5 Peak Limits) TYPICAL PERFORMANCE CHARACTERISTICS Conducted EMI Performance DC2468A DEMO BOARD (WITH EMI FIL TER INSTALLED) 14V INPUT TO 5V OUTPUT AT 4A, f SW = 2MHz FIXED FREQUENCY MODE SPREAD SPECTRUM MODE FREQUENCY (MHz) –40 –30 –20 –10 AMPLITUDE (dBµV) 8645S G49 VERTICAL POLARIZATION PEAK DETECTOR 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) 8645S G50 DC2468A DEMO BOARD (WITH EMI FIL TER INSTALLED) 14V INPUT TO 5V OUTPUT AT 4A, f SW = 2MHz HORIZONTAL POLARIZATION PEAK DETECTOR 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) 8645S G51

Rev. B For more information www.analog.com PIN FUNCTIONS BIAS (Pin 1): 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 V OUT. 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. INTV CC (Pin 2): Internal 3.4V Regulator Bypass Pin. The internal power drivers and control circuits are powered from this voltage. INTV CC maximum output current is 25mA. 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. This pin should be floated. NC (Pins 3, 7, 20, 24): No Connect. This pin is not con- nected to internal circuitry and can be tied anywhere on the PCB, typically ground. V IN (Pins 4, 5, 6, 21, 22, 23): The V IN pins supply cur- rent to the LT8645S/LT8646S internal circuitry and to the internal topside power switch. These pins must be tied together and be locally bypassed with a capacitor of 4.7µF or more. Be sure to place the positive terminal of the input capacitor as close as possible to the V IN pins, and the negative capacitor terminal as close as possible to the GND pins. See the Applications Information section for a sample layout. GND (Pins 8, 9, 10, 17, 18, 19, Exposed Pad Pins 33–38): Ground. Place the negative terminal of the input capacitor as close to the GND pins as possible. See the Applications Information section for a sample layout. The exposed pads should be soldered to the PCB for good thermal performance. If necessary due to manufacturing limitations Pins 33 to 38 may be left disconnected, however thermal performance will be degraded. BST (Pin 11): This pin is used to provide a drive voltage, higher than the input voltage, to the topside power switch. This pin should be floated. SW (Pins 12, 13, 14, 15, 16): The SW pins are the outputs of the internal power switches. Tie these pins together and connect them to the inductor and boost capacitor . This node should be kept small on the PCB for good performance and low EMI. EN/UV (Pin 25): The LT8645S/LT8646S is shut down when this pin is low and active when this pin is high. The hysteretic threshold voltage is 1.01V going up and 0.965V going down. Tie to V IN if the shutdown feature is not used. An external resistor divider from VIN can be used to program a V IN threshold below which the LT8645S/ LT8646S will shut down. RT (Pin 26): A resistor is tied between RT and ground to set the switching frequency. CLKOUT (Pin 27): In pulse-skipping mode, spread spec- trum, 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 INTV CC 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. SYNC/MODE (Pin 28): This pin programs four different operating modes: 1) Burst Mode. Tie this pin to ground for Burst Mode operation at low output loads—this will result in ultralow quiescent current. 2) Pulse-skipping mode. This mode offers full frequency operation down to low output loads before pulse skipping occurs. Float this pin for pulse-skipping mode. When floating, pin leakage currents should be <1µA. 3) Spread spectrum mode. Tie this pin high to INTV CC (~3.4V) or an external supply of 3V to 4V for pulse-skipping 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 pulse- skipping mode.

Rev. BFor more information www.analog.com PIN FUNCTIONS TR/SS (Pin 29): Output T racking and Soft-Start Pin. This pin allows user control of output voltage ramp rate during start-up. For the LT8645S, a TR/SS voltage below 0.97V forces it to regulate the FB pin to equal the TR/SS pin volt- age. When TR/SS is above 0.97V, the tracking function is disabled and the internal reference resumes control of the error amplifier. For the LT8646S, 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 INTV CC 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. GND (Pin 30 LT8645S Only): Ground. Connect this pin to system ground and to the ground plane. This pin is also connected to ground internally, and can be left floating on PCB to be pin compatible with the LT8646S. V C (Pin 30, LT8646S Only): The VC pin is the output of the internal error amplifier . The voltage on this pin controls the peak switch current. Tie an R C network from this pin to ground to compensate the control loop. PG (Pin 31): 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 pulled low when EN/UV is below 1V, INTV CC has fallen too low, VIN is too low, or thermal shutdown. PG is valid when VIN is above 3.4V. FB (Pin 32): The LT8645S/LT8646S regulates the FB pin to 0.97V. Connect the feedback resistor divider tap to this pin. Also, connect a phase lead capacitor between FB and V OUT. Typically, this capacitor is 1pF to 10pF. Corner Pins: These pins are for mechanical support only and can be tied anywhere on the PCB, typically ground.

Rev. B For more information www.analog.com BLOCK DIAGRAM ++– SLOPE COMP INTERNAL 0.97V REF OSCILLATOR 200kHz TO 2.2MHz BURST DETECT 3.4V REG CBST 0.22µF COUT VOUT 8645s BD SW L BST 12-16 21-23 ERROR AMP SHDN ±8% VC SHDN THERMAL SHDN INTV CC UVLO VIN UVLO SHDN THERMAL SHDN V IN UVLO EN/UV 1.01V + –25 GND 33-38 INTVCC 2 BIAS 1 VIN 13 GND GND 8-10 17-19 CLKOUT PG31 FB OPT OPT RT CSS OPT VOUT TR/SS 1.9µA 60k INTVCC RT26 SYNC/MODE28 VIN 4-6 VIN COPT1CIN3 CIN1 20nF CVCC 2.2µF COPT2CIN2 20nF SWITCH LOGIC AND ANTI- SHOOT THROUGH 600k L T8645S ONL Y L T8645S ONL Y VCL T8646S ONL Y30 CF CC RC

Rev. BFor more information www.analog.com OPERATION The LT8645S/LT8646S 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 internal 0.97V reference. When the load current increases it causes a reduction in the feedback voltage relative to the reference leading the error amplifier to raise the VC voltage until the average inductor current matches the new load current. When the top power switch turns off, the synchronous power switch turns on until the next clock cycle begins or inductor current falls to zero. If overload conditions result in more than 11A flowing through the bottom switch, the next clock cycle will be delayed until switch current returns to a safe level. The “S” in LT8645S/LT8646S refers to the second genera- tion Silent Switcher technology. This technology allows fast switching edges for high efficiency at high switching frequencies, while simultaneously achieving good EMI performance. This includes the integration of ceramic capacitors into the package for V IN, BST , and INTVCC (see Block Diagram). These caps keep all the fast AC current loops small, which improves EMI performance. If the EN/UV pin is low, the LT8645S/LT8646S is shut down and draws approximately 1µA from the input. When the EN/UV pin is above 1.01V, the switching regulator will become active. To optimize efficiency at light loads, the LT8645S/LT8646S 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 sup - ply current to 1.7μA (LT8645S) or 230μA (LT8646S with BIAS = 0). In a typical application, 2.5μA (LT8645S) or 120μA (LT8646S with BIAS = 5V OUT) 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 pulse-skipping mode. If a clock is applied to the SYNC/MODE pin, the part will synchronize to an external clock frequency and operate in pulse-skipping mode. While in pulse-skipping mode the oscillator operates continuously and positive SW transitions are aligned to the clock. During light loads, switch pulses are skipped to regulate the output and the quiescent current will be several hundred µA. To improve EMI, the LT8645S/LT8646S can operate in spread spectrum mode. This feature varies the clock with a triangular frequency modulation of +20%. For example, if the LT8645S/LT8646S’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 INTV CC (~3.4V) or an external supply of 3V to 4V to enable spread spectrum modulation with pulse-skipping 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 V IN. The BIAS pin should be connected to VOUT if the LT8645S/LT8646S output is programmed at 3.3V to 25V. The V C pin optimizes the loop compensation of the switching regulator based on the programmed switching frequency, allowing for a fast transient response. The VC pin also enables current sharing and a CLKOUT pin enables synchronizing other regulators to the LT8646S. Comparators monitoring the FB pin voltage will pull the PG pin low if the output voltage varies more than ±8% (typical) from the set point, or if a fault condition is present. The oscillator reduces the LT8645S/LT8646S’s operat - ing 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.

See Figure 1 for recommended PCB layouts. Figure 1. Recommended PCB Layouts for the LT8645S and LT8646S

Board guide for the LT8645S/LT8646S. or 0805 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. board and on the bottom side. the output power is supplied by the output capacitor . Figure 2. SW Frequency vs Load Information in Burst Mode Operation (2a) and Pulse-Skipping Mode (2b)

Rev. B For more information www.analog.com APPLICATIONS INFORMATION loads, the current in the feedback resistor divider must be minimized as it appears to the output as load current. In order to achieve higher light load efficiency, more energy must be delivered to the output during the single small pulses in Burst Mode operation such that the LT8645S/ LT8646S can stay in sleep mode longer between each pulse. This can be achieved by using a larger value inductor (i.e., 4.7µH), and should be considered independent of switch- ing frequency when choosing an inductor . For example, while a lower inductor value would typically be used for a high switching frequency application, if high light load efficiency is desired, a higher inductor value should be chosen. See curve in Typical Performance Characteristics. While in Burst Mode operation the current limit of the top switch is approximately 1.25A (as shown in Figure 3), resulting in low output voltage ripple. Increasing the output capacitance will decrease output ripple proportionally. As load ramps upward from zero the switching frequency will increase but only up to the switching frequency pro- grammed by the resistor at the R T pin as shown in Figure 2a. The output load at which the LT8645S/LT8646 S 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). Pulse-Skipping Mode For some applications it is desirable for the LT8645S/ LT8646S to operate in pulse-skipping mode, offering two major differences from Burst Mode operation. First is the clock stays awake at all times and all switching cycles are aligned to the clock. In this mode much of the internal circuitry is awake at all times, increasing quiescent cur - rent to several hundred µA. Second is that full switching frequency is reached at lower output load than in Burst Mode operation (see Figure 2b). To enable pulse-skipping mode, float the SYNC/MODE pin. Leakage current in this pin should be <1µA. See Block Diagram for internal pull-up and pull-down resistance. Spread Spectrum Mode The LT8645S/LT8646S 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 LT8645S/LT8646S is programmed to 2MHz, the frequency will vary from 2MHz to 2.4MHz at Figure 3. Burst Mode Operation Switching Waveforms, Burst Mode Operation FRONT PAGE APPLICATION 12V IN TO 5V OUT AT 10mA V SYNC = 0V 10µs/DIV V SW 5V/DIV I L 500mA/DIV 8645S F03

Rev. BFor more information www.analog.com APPLICATIONS INFORMATION a 3kHz rate. When spread spectrum operation is selected, Burst Mode operation is disabled, and the part will run in pulse-skipping mode. Synchronization To synchronize the LT8645S/LT8646S oscillator to an external 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 LT8645S/LT8646S will not enter Burst Mode opera- tion at low output loads while synchronized to an external clock, but instead will pulse-skip to maintain regulation. The LT8645S/LT8646S may be synchronized over a 200kHz to 2.2MHz range. The RT resistor should be chosen to set the LT8645S/LT8646S switching frequency equal to or below the lowest synchronization input. For example, if the synchronization signal will be 500kHz and higher , the RT should be selected for 500kHz. The slope compensation is set by the RT value, while the minimum slope compensation required to avoid subharmonic oscillations is established by the inductor size, input voltage, and output voltage. Since the synchronization frequency will not change the slopes of the inductor current waveform, if the inductor is large enough to avoid subharmonic oscillations at the frequency set by RT , then the slope compensation will be sufficient for all synchronization frequencies. The LT8645S/LT8646S does not operate in forced continu- ous mode regardless of SYNC/MODE signal. FB Resistor Network The output voltage is programmed with a resistor divider between the output and the FB pin. Choose the resistor values according to: R1= R2 VOUT 0.97V −1⎛ ⎝⎜ ⎞ (1) Reference designators refer to the Block Diagram. 1% resistors are recommended to maintain output voltage accuracy For the LT8645S, if low input quiescent current and good light-load efficiency are desired, use large resistor values for the FB resistor divider . The current flowing in the divider acts as a load current, and will increase the no-load input current to the converter , which is approximately: IQ = 1.7µA + VOUT R1+R2 ⎝⎜ ⎞ VOUT VIN n ⎝⎜ ⎞ (2) where 1.7µA is the quiescent current of the LT8645S and the second term is the current in the feedback divider reflected to the input of the buck operating at its light load efficiency n. For a 3.3V application with R1 = 1M and R2 = 412k, the feedback divider draws 2.3µA. With V IN = 12V and n = 80%, this adds 0.8µA to the 1.7µA quiescent current resulting in 2.5µA no-load current from the 12V supply. Note that this equation implies that the no-load current is a function of V IN; this is plotted in the Typical Performance Characteristics section. When using large FB resistors, a 1pF to 10pF phase-lead capacitor should be connected from VOUT to FB. Setting the Switching Frequency The LT8645S/LT8646S uses a constant frequency PWM architecture that can be programmed to switch from 200kHz to 2.2MHz by using a resistor tied from the RT pin to ground. A table showing the necessary R T value for a desired switching frequency is in Table 1. The RT resistor required for a desired switching frequency can be calculated using: RT = 46.5 fSW – 5.2 (3) where RT is in kΩ and f SW is the desired switching fre- quency in MHz.

Table 1. SW Frequency vs RT Value are lower efficiency and a smaller input voltage range. current to assure safe operation. lower switching frequency than programmed by RT . dropped to achieve higher duty cycle. and L is the inductor value in μH.

Rev. BFor more information www.analog.com APPLICATIONS INFORMATION 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 2A output should use an inductor with an RMS rating of greater than 2A and an I SAT of greater than 3A. 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 LT8645S/LT8646S limits the peak switch current in order to protect the switches and the system from overload faults. The top switch current limit (I LIM) is 14A at low duty cycles and decreases linearly to 11.5A at DC = 0.9. The inductor value must then be sufficient to supply the desired maximum output current (I OUT(MAX)), which is a function of the switch current limit (ILIM) and the ripple current. 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 fSW is the switching frequency of the LT8645S/ LT8646S, and L is the value of the inductor . Therefore, the maximum output current that the LT8645S/LT8646S 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 OUT(MAX)) given the switching frequency, and maximum input voltage used in the desired application. When operating at high V IN (greater than 40V) and at a frequency and duty cycle that would require a switch on- time of less than 100ns, choose an inductor such that the ∆IL is greater than 1.5A in order to prevent duty cycle jitter . In order to achieve higher light load efficiency, more energy must be delivered to the output during the single small pulses in Burst Mode operation such that the LT8645S/ LT8646S can stay in sleep mode longer between each pulse. This can be achieved by using a larger value inductor (i.e., 4.7µH), and should be considered independent of switch- ing frequency when choosing an inductor . For example, while a lower inductor value would typically be used for a high switching frequency application, if high light load efficiency is desired, a higher inductor value should be chosen. See curve in Typical Performance Characteristics. The optimum inductor for a given application may differ from the one indicated by this design guide. A larger value inductor provides a higher maximum load current and reduces the output voltage ripple. For applications requiring smaller load currents, the value of the inductor may be lower and the LT8645S/LT8646S 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 • fSW (10) where DC is the duty cycle ratio (VOUT/VIN) and fSW is the switching frequency. Input Capacitors The VIN of the LT8645S/LT8646S should be bypassed with at least three ceramic capacitors for best perfor - mance. T wo small ceramic capacitors of 0.47µF can be placed close to the part; one on each side of the device

Rev. B For more information www.analog.com APPLICATIONS INFORMATION (COPT1, COPT2). These capacitors should be 0603 or 0805 in size. For automotive applications requiring 2 series input capacitors, two small 0603 or 0805 may be placed at each side of the LT8645S/LT8646S. A third, larger ceramic capacitor of 4.7µF or larger should be placed close to C OPT1 or COPT2. 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 circuit. If the LT8645S/LT8646S circuit is plugged into a live supply, the input voltage can ring to twice its nominal value, possibly exceeding the LT8645S/LT8646S’s voltage rating. This situation is easily avoided (see Analog Devices Application Note 88). Output Capacitor and Output Ripple The output capacitor has two essential functions. Along with the inductor , it filters the square wave generated by the LT8645S/LT8646S to produce the DC output. In this role it determines the output ripple, thus low impedance at the switching frequency is important. The second function is to store energy in order to satisfy transient loads and stabilize the LT8645S/LT8646S’s control loop. Ceramic capacitors have very low equivalent series resistance (ESR) and provide the best ripple performance. For good starting values, see the Typical Applications section. Use X5R or X7R types. This choice will provide low output ripple and good transient response. T ransient performance can be improved with a higher value output capacitor and the addition of a feedforward capacitor placed between V OUT and FB. Increasing the output capacitance will also decrease the output voltage ripple. A lower value of output capacitor can be used to save space and cost but transient performance will suffer and may cause loop instability. See the Typical Applications in this data sheet for suggested capacitor values. When choosing a capacitor , special attention should be given to the data sheet to calculate the effective capacitance under the relevant operating conditions of voltage bias and temperature. A physically larger capacitor or one with a higher voltage rating may be required. Ceramic Capacitors Ceramic capacitors are small, robust and have very low ESR. However , ceramic capacitors can cause problems when used with the LT8645S/LT8646S due to their piezoelectric nature. When in Burst Mode operation, the LT8645S/LT8646S’s switching frequency depends on the load current, and at very light loads the LT8645S/LT8646S can excite the ceramic capacitor at audio frequencies, generating audible noise. Since the LT8645S/LT8646S operates at a lower current limit during Burst Mode op - eration, 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 LT8645S/LT8646S. As previously mentioned, a ceramic input capacitor combined with trace or cable inductance forms a high quality (un - derdamped) tank circuit. If the LT8645S/LT8646S circuit is plugged into a live supply, the input voltage can ring to twice its nominal value, possibly exceeding the LT8645S/ LT8646S’s rating. This situation is easily avoided (see Analog Devices Application Note 88). Enable Pin The LT8645S/LT8646S is in shutdown when the EN pin is low and active when the pin is high. The rising threshold of the EN comparator is 1.01V, with 45mV 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 LT8645S/LT8646S to regulate the output only when VIN is above a desired voltage (see the Block Diagram). Typically, this threshold, VIN(EN), is used in situations where the input

Rev. B For more information www.analog.com PACKAGE DESCRIPTION 32-Lead (6mm × 4mm × 0.94mm) (Reference L TC DWG # 05-08-1512 Rev C) DETAIL B A PACKAGE TOP VIEW PIN 1 CORNER Y X aaa Z2× ddd Z 32× 32b PACKAGE BOTTOM VIEW SEE NOTES E D b 0.375 e e e b 0.375 0.20 0.20 1.355 1.355 1.34 1.125 LQFN 32 0818 REV C TRAY PIN 1 BEVEL PACKAGE IN TRAY LOADING ORIENTATION COMPONENT PIN 1 SYMBOL A L b D E e aaa bbb ccc ddd eee fff NOM 0.94 0.02 0.40 0.25 4.00 6.00 2.45 4.45 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 SUBSTRATE THK MOLD CAP HT DIMENSIONS DETAIL B SUBSTRATE MOLD CAP // bbb Z Z Z DETAIL A DETAIL C DETAIL C SUGGESTED PCB LAYOUT TOP VIEW 0.0000 0.0000 0.2500 0.2500 0.7500 0.7500 1.2500 1.2500 1.7500 1.7500 2.2500 2.2500 1.2500 0.7500 0.2500 0.2500 1.2500 0.7500 DETAIL A PIN 1 NOTCH 0.25 × 45° L TXXXXXX 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 IS SEGMENTED AND ARRANGED

IN A MATRIX FORMAT . IT MAY HAVE OPTIONAL CORNER RADII ON EACH SEGMENT

7 CORNER SUPPORT PAD CHAMFER IS OPTIONAL

aaa Z 2× M X Y Z ccc MXY Z ccc M X Y Z eee M Zfff 0.20 0.20 1.355 1.355 1.34 1.125 PACKAGE OUTLINE 0.25 ±0.05 0.70 ±0.05 6.50 ±0.05 4.50 ±0.05 L e/2 0.375 0.375 MIN 0.85 0.01 0.30 0.22

Rev. BFor 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 01/18 Added LT8646S All B 04/20 Added AEC-Q100 qualified statement. Inserted devices options table. Removed EMC word. Updated Pin Configuration figure descriptions. Updated Ordering Information table with #W devices. Text and Figures 4, 5,12 and editing. Update Package Description to match Rev C. All 21, 22, 27

Rev. B For more information www.analog.com  ANALOG DEVICES, INC. 2017-2020 www.analog.com RELATED PARTS TYPICAL APPLICATIONS 1.8V, 8A Step-Down Converter PART NUMBER DESCRIPTION COMMENTS LT8640S 42V, 6A Synchronous Step-Down Silent Switcher 2 with 2.5µA Quiescent Current VIN(MIN) = 3.4V, VOUT(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 I Q = 2.5µA VIN(MIN) = 3.4V, VIN(MAX) = 42V, VOUT(MIN) = 0.97V, IQ = 2.5μA, ISD < 1μA, 3mm × 4mm QFN-18 LT8641 65V, 3.5A, 95% Efficiency, 3MHz Synchronous MicroPower Step-Down DC/DC Converter with I Q = 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 I Q = 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 I Q = 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 I Q = 2.5µA VIN(MIN) = 3.4V, VIN(MAX) = 42V, VOUT(MIN) = 0.97V, IQ = 2.5μA, ISD < 1μA, MSOP-16E LT8611 42V, 2.5A, 96% Efficiency, 2.2MHz Synchronous MicroPower Step-Down DC/DC Converter with I Q = 2.5µA and Input/Output Current Limit/Monitor VIN(MIN) = 3.4V, VIN(MAX) = 42V, VOUT(MIN) = 0.97V, IQ = 2.5μA, ISD < 1μA, 3mm × 5mm QFN-24 LT8616 42V, Dual 2.5A + 1.5A, 95% Efficiency, 2.2MHz Synchronous MicroPower Step-Down DC/DC Converter with I Q = 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 I Q = 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 I Q = 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 I Q = 2.5µA VIN(MIN) = 3.4V, VIN(MAX) = 42V, VOUT(MIN) = 0.97V, IQ = 3.0μA, ISD < 1μA, 3mm × 6mm QFN-28 LT8613 42V, 6A, 96% Efficiency, 2.2MHz Synchronous MicroPower Step-Down DC/DC Converter with Current Limiting V IN(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 I Q = 25µA VIN(MIN) = 3V, VIN(MAX) = 42V, VOUT(MIN) = 0.8V, IQ = 2.5μA, ISD < 1μA, 6mm × 6mm QFN-40 L T8645S SW BIAS FB V IN 3.4V TO 30V (65V TRANSIENT) GND RT V IN EN/UV V OUT 1.8V 4.7pF 4.7µF 41.2k 866k 0.82µH f SW = 1MHz L: XEL6030 1µF EXTERNAL SOURCE >3.1V OR GND 8645S TA02 47µF 1210 X5R/X7R PINS NOT USED IN THIS CIRCUIT: BST , CLKOUT , INTVCC, PG, SYNC/MODE, TR/SS