LT8645SHV-2#PBF

LT8645S-2 65V, 8A Synchronous Step-Down Silent Switcher with 2.5µA Quiescent Current FEATURES DESCRIPTION Silent Switcher® Architecture n Ultralow EMI Emissions n Optional Spread Spectrum Modulation n High Efficiency at High Frequency n Up to 95% Efficiency at 1MHz, 12V to 5V IN OUT n Up to 94% Efficiency at 2MHz, 12V to 5V IN OUT n Wide Input Voltage Range: 3.4V to 65V n Ultralow Quiescent Current Burst Mode Operation n 2.5μA I Regulating 12V to 3.3V Q IN OUT n Output Ripple < 10mV P-P n Fast Minimum Switch On-Time: 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 Tracking n Small 32-Lead 6mm × 4mm LQFN Package n AEC-Q100 Qualified for Automotive Applications The LT®8645S-2 synchronous step-down regulator features Silent Switcher architecture designed to minimize EMI emissions while delivering high efficiency at high switching frequencies. This performance makes the LT8645S-2 ideal for noise sensitive applications and environments. n The fast, clean, low-overshoot switching edges enable high efficiency operation even at high switching frequencies, 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. 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. APPLICATIONS Automotive and Industrial Supplies n General Purpose Step-Down n GSM Power Supplies n INTERNAL CAPS VC COMP 150ºC GRADE LT8645S* Yes Internal No LT8646S* Yes External No LT8645S-2 No Internal Yes *See LT8645S/LT8646S Data Sheet All registered trademarks and trademarks are the property of their respective owners. Protected by U.S. patents, including 8823345. TYPICAL APPLICATION 5V 8A Step-Down Converter 12VIN to 5VOUT Efficiency VIN 5.5V TO 65V 0.47µF EN/UV VIN 0.47µF BST 0.1µF SW 2.2µH VOUT 5V 8A BIAS 1µF 41.2k fSW = 1MHz INTVCC 2.2pF RT 3.5 100µF 243k 2.5 80 2.0 1.5 75 POWER LOSS 65 60 8645S-2 TA01a 3.0 EFFICIENCY 85 70 1M FB GND 95 90 GND LT8645S-2 4.0 1 2 POWER LOSS (W) GND VIN EFFICIENCY (%) 4.7µF 100 1.0 1MHz, L = 2.2µH 0.5 2MHz, L = 1µH 0 3 4 5 6 7 8 LOAD CURRENT (A) 8645S-2 TA01b Rev. A Document Feedback For more information www.analog.com 1 LT8645S-2 PIN CONFIGURATION 2 NC 3 VIN 4 VIN 5 VIN 6 NC 7 GND 8 GND 9 GND 10 PG GND TR/SS SYNC/MODE CLKOUT 31 30 29 28 27 26 RT 33 GND 25 EN/UV 34 GND 24 NC 23 VIN 35 GND 22 VIN 36 GND 21 VIN 20 NC 37 GND 19 GND 38 GND 18 GND 17 GND 11 12 13 14 15 SW INTVCC 32 SW 1 SW BIAS FB TOP VIEW 16 SW VIN, EN/UV.................................................................65V PG..............................................................................42V BIAS...........................................................................25V FB, TR/SS ...................................................................4V SYNC/MODE Voltage ..................................................6V Operating Junction Temperature Range (Note 2) LT8645S-2E........................................ –40°C to 125°C LT8645S-2J........................................ –40°C to 150°C LT8645S-2H....................................... –40°C to 150°C Storage Temperature Range................... –65°C to 150°C Maximum Reflow (Package Body) Temperature.... 260°C SW (Note 1) BST ABSOLUTE MAXIMUM RATINGS 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 ORDER INFORMATION PART NUMBER PART MARKING* FINISH CODE PAD FINISH PACKAGE TYPE** Au (RoHS) LQFN (Laminate Package with QFN Footprint) Au (RoHS) LQFN (Laminate Package with QFN Footprint) LT8645SEV-2#PBF LT8645SJV-2#PBF 86452 e4 LT8645SHV-2#PBF MSL RATING TEMPERATURE RANGE –40°C to 125°C 3 –40°C to 150°C AUTOMOTIVE PRODUCTS*** LT8645SEV-2#WPBF LT8645SJV-2#WPBF 86452 e4 LT8645SHV-2#WPBF • Contact the factory for parts specified with wider operating temperature ranges. *Pad or ball finish code is per IPC/JEDEC J-STD-609. –40°C to 125°C 3 –40°C to 150°C • 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-2 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. 2 Rev. A For more information www.analog.com LT8645S-2 ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. PARAMETER CONDITIONS Minimum Input Voltage VIN Quiescent Current in Shutdown VIN Quiescent Current in Sleep MIN TYP MAX l 3.0 3.4 V l 0.9 0.9 3 20 µA µA l 1.7 1.7 4 20 µA µA VEN/UV = 0V VEN/UV = 2V, VFB > 0.97V, VSYNC = 0V VIN Current in Regulation VOUT = 0.97V, VIN = 6V, ILOAD = 1mA, VSYNC = 0V Feedback Reference Voltage VIN = 6V VIN = 6V l Feedback Voltage Line Regulation VIN = 4.0V to 42V l Feedback Pin Input Current VFB = 1V BIAS Pin Current Consumption VBIAS = 3.3V, fSW = 2MHz Minimum On-Time ILOAD = 2.5A, SYNC = 0V ILOAD = 2.5A, SYNC = 2V l 0.964 0.956 RT = 221k RT = 60.4k RT = 18.2k Top Power NMOS On-Resistance ISW = 1A 500 µA 0.976 0.982 V V 0.004 0.025 %/V 20 nA 22 Minimum Off-Time Oscillator Frequency 200 0.970 0.970 –20 l l l l l 180 665 1.8 l 10.5 mA 40 35 65 60 ns ns 80 110 ns 210 700 1.95 240 735 2.1 kHz kHz MHz 36 Top Power NMOS Current Limit Bottom Power NMOS On-Resistance VINTVCC = 3.4V, ISW = 1A Bottom Power NMOS Current Limit VINTVCC = 3.4V 8.5 SW Leakage Current VIN = 42V, VSW = 0V, 42V –1.5 EN/UV Pin Threshold EN/UV Rising 14 mΩ 17.5 25 l 0.95 EN/UV Pin Hysteresis 11 1.01 VEN/UV = 2V PG Upper Threshold Offset from VFB PG Lower Threshold Offset from VFB –20 VFB Falling l 5 VFB Rising l –10.5 PG Hysteresis A mΩ 14 A 1.5 µA 1.07 45 EN/UV Pin Current UNITS V mV 20 nA 7.5 10 % –8 –5.5 % 40 nA 750 2000 Ω 0.9 1.2 2.55 1.4 2.9 V V V 0.4 –40 % PG Leakage VPG = 3.3V PG Pull-Down Resistance VPG = 0.1V l SYNC/MODE Threshold SYNC/MODE DC and Clock Low Level Voltage SYNC/MODE Clock High Level Voltage SYNC/MODE DC High Level Voltage l l l Spread Spectrum Modulation Frequency Range RT = 60.4k, VSYNC = 3.3V 24 % Spread Spectrum Modulation Frequency VSYNC = 3.3V 2.5 kHz TR/SS Source Current TR/SS Pull-Down Resistance l Fault Condition, TR/SS = 0.1V 0.7 2.2 1.2 2 220 2.8 µA Ω Rev. A For more information www.analog.com 3 LT8645S-2 ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. 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 LT8645S-2E 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 LT8645S-2J and LT8645S-2H are guaranteed over the full –40°C to 150°C operating junction temperature range. High junction temperatures degrade operating lifetimes. Operating lifetime is derated at junction temperatures greater than 125°C. The junction temperature (TJ, in °C) is calculated from 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. 4 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. Rev. A For more information www.analog.com LT8645S-2 TYPICAL PERFORMANCE CHARACTERISTICS 12VIN to 3.3VOUT Efficiency vs Frequency 4.0 100 3.5 95 EFFICIENCY 3.0 2.0 1.5 75 POWER LOSS 2 75 3 4 5 6 LOAD CURRENT (A) 7 8 70 0.5 65 0 60 1.5 POWER LOSS 1 L = XEL6060 1.0 500kHz, L = 2.7µH 1MHz, L = 1.5µH 0.5 2MHz, L = 0.82µH 0 3 4 5 6 7 8 LOAD CURRENT (A) 2 8645S-2 G01 1.6 65 1.2 POWER LOSS 0 1 2 3 4 5 LOAD CURRENT (A) EFFICIENCY (%) 80 POWER LOSS (W) EFFICIENCY (%) 80 2.0 60 70 60 50 VIN = 12V VIN = 24V VIN = 36V VIN = 48V 40 VIN = 12V 0.8 VIN = 24V VIN = 36V 0.4 VIN = 48V 0 6 7 8 30 20 0.01 0.1 1 10 100 LOAD CURRENT (mA) 80 0.4 EFFICIENCY (%) EFFICIENCY (%) 85 50 2.2 8645S-2 G07 VIN = 12V VIN = 24V VIN = 36V VIN = 48V fSW = 500kHz L = WE–LHMI7050, 4.7µH 0.1 1 10 100 LOAD CURRENT (mA) 80 65 1000 Reference Voltage Reference Voltage 977 VIN = 24V VOUT = 5V ILOAD = 10mA L = WE–LHMI7050 70 0.7 1 1.3 1.6 1.9 SWITCHING FREQUENCY (MHz) 0 8645S-2 G06 VIN = 12V 75 VOUT = 3.3V ILOAD = 2A L = XEL6060, 4.7µH 8 60 20 0.01 1000 90 VIN = 24V 7 979 95 VIN = 12V 88 82 3 4 5 6 LOAD CURRENT (A) 0.4 Low Load Efficiency at 3.3VOUT 30 100 90 84 2 0.8 70 Burst Mode Operation Efficiency vs Inductor Value 96 86 1 8645S-2 G05 Efficiency vs Frequency 92 0 40 fSW = 500kHz L = WE–LHMI7050, 4.7µH 8645S-2 G04 94 POWER LOSS 1.2 VIN = 12V VIN = 24V VIN = 36V VIN = 48V 8645S-2 G03 90 70 50 50 90 2.4 fSW = 500kHz L = XEL6060, 2.7µH 55 55 3.6 2.8 75 1.6 65 100 85 80 2.0 70 100 3.2 2.4 75 4.0 90 2.8 fSW = 500kHz L = XEL6060, 2.7µH 80 Low Load Efficiency at 5VOUT EFFICIENCY 95 85 8645S-2 G02 Efficiency at 3.3VOUT 100 3.6 3.2 60 EFFICIENCY (%) 1 2.0 4.0 EFFICIENCY 90 REFERENCE VOLTAGE (mV) 60 2.5 80 L = XEL6060 1.0 500kHz, L = 2.7µH 1MHz, L = 2.2µH 2MHz, L = 1µH 65 EFFICIENCY (%) 80 3.5 95 3.0 EFFICIENCY 85 100 POWER LOSS (W) 2.5 90 4.0 POWER LOSS (W) 85 70 95 POWER LOSS (W) EFFICIENCY (%) 90 Efficiency at 5VOUT 100 EFFICIENCY (%) 12VIN to 5VOUT Efficiency vs Frequency 1 2 3 4 5 6 7 8 INDUCTOR VALUE (µH) 9 975 973 971 969 967 965 963 10 8645S-2 G08 961 –50 –25 0 25 50 75 100 125 150 TEMPERATURE (°C) 8645S2 G09 Rev. A For more information www.analog.com 5 LT8645S-2 TYPICAL PERFORMANCE CHARACTERISTICS EN Pin Thresholds Load Regulation 1.02 1.00 0.99 0.98 EN FALLING 0.97 0.20 0.15 0.15 0.10 0.05 0 VOUT = 5V VIN = 12V VSYNC = 0V –0.05 0.96 0.95 –50 –25 0 25 50 75 100 125 150 TEMPERATURE (°C) –0.10 0 1 2 3 4 5 6 LOAD CURRENT (A) 5 15 25 35 45 INPUT VOLTAGE (V) 55 65 8645S-2 G12 Top FET Current Limit 16 15 CURRENT LIMIT (A) 2.0 13.5 13.0 12.5 12.0 1.5 5% DC 14 13 11.5 0 10 20 30 40 50 INPUT VOLTAGE (V) 11.0 0.1 60 0.3 0.5 DUTY CYCLE 0.7 8645S-2 G13 SWITCH DROP (mV) 80 60 TOP SWITCH BOTTOM SWITCH 20 0 –50 400 300 350 250 TOP SWITCH 150 100 BOTTOM SWITCH 50 –25 0 25 50 75 TEMPERATURE (°C) 100 125 8645S-2 G16 0 25 50 75 100 125 150 TEMPERATURE (°C) Dropout Voltage 350 200 0 8645S-2 G15 Switch Drop vs Switch Current SWITCH CURRENT = 1A 40 12 –50 –25 0.9 8645S-2 G14 Switch Drop vs Temperature SWITCH DROP (mV) –0.10 VOUT = 5V ILOAD = 2A 14.5 CURRENT LIMIT (A) INPUT CURRENT (µA) 2.5 6 8 14.0 3.0 100 –0.05 15.0 VOUT = 3.3V L = 4.7µH IN-REGULATION 3.5 1.0 0.00 Top FET Current Limit vs Duty Cycle No-Load Supply Current 4.0 0.05 8645S-2 G11 8645S-2 G10 4.5 7 0.10 DROPOUT VOLTAGE (mV) EN THRESHOLD (V) CHANGE IN VOUT (%) EN RISING 1.01 Line Regulation 0.20 CHANGE IN VOUT (%) 1.03 VIN = 5V VOUT SET TO REGULATE AT 5V L = XEL6060, 1µH 300 250 200 150 100 50 0 1 2 3 4 5 SWITCH CURRENT (A) 6 7 8645S-2 G17 0 0 1 2 3 4 5 LOAD CURRENT (A) 6 7 8645S-2 G18 Rev. A For more information www.analog.com LT8645S-2 TYPICAL PERFORMANCE CHARACTERISTICS Minimum On-Time Switching Frequency 740 BURST MODE OPERATION PULSE–SKIPPING MODE SWITCHING FREQUENCY (kHz) MINIMUM ON-TIME (ns) 40 35 30 25 –50 ILOAD = 3A VOUT = 0.97V fSW = 2.2MHz –25 0 25 50 75 TEMPERATURE (°C) RT = 60.4k 730 45 100 Burst Frequency 1200 SWITCHING FREQUENCY (kHz) 50 720 710 700 690 680 670 660 –50 –25 125 0 2.1 150 SS PIN CURRENT (µA) FB VOLTAGE (V) LOAD CURRENT (mA) 200 0.8 0.6 0.4 100 0.2 50 55 0 100 200 300 400 LOAD CURRENT (mA) 500 0 65 600 Soft-Start Current 2.2 1.0 250 FRONT PAGE APPLICATION VIN = 12V VOUT = 5V 200 8645S-2 G21 1.2 FRONT PAGE APPLICATION 350 VOUT = 5V fSW = 1MHz 300 VSYNC = Float 25 35 45 INPUT VOLTAGE (V) 400 Soft-Start Tracking 400 15 600 8645S-2 G20 Minimum Load to Full Frequency (Pulse-Skipping Mode) 5 800 0 25 50 75 100 125 150 TEMPERATURE (°C) 8645S-2 G19 0 1000 VSS = 0.5V 2.0 1.9 1.8 1.7 1.6 1.5 0 0.2 8645S-2 G22 1.0 0.4 0.6 0.8 TR/SS VOLTAGE (V) 1.2 1.4 –50 –25 1.4 0 25 50 75 100 125 150 TEMPERATURE (°C) 8645S-2 G24 8645S-2 G23 PG THRESHOLD OFFSET FROM VREF (%) PG THRESHOLD OFFSET FROM VREF (%) 10.0 9.5 9.0 8.5 FB RISING 8.0 7.5 7.0 FB FALLING 6.5 6.0 –50 –25 0 RT Programmed Switching Frequency PG Low Thresholds 25 50 75 100 125 150 TEMPERATURE (°C) 8645S-2 G25 –6.0 250 –6.5 225 200 –7.0 –7.5 RT PIN RESISTOR (kΩ) PG High High Thresholds Thresholds PG FB RISING –8.0 –8.5 FB FALLING –9.0 150 125 100 75 50 –9.5 –10.0 –50 –25 175 25 0 25 50 75 100 125 150 TEMPERATURE (°C) 8645S-2 G26 0 0.2 0.6 1.4 1.8 1 SWITCHING FREQUENCY (MHz) 2.2 8645S-2 G27 Rev. A For more information www.analog.com 7 LT8645S-2 TYPICAL PERFORMANCE CHARACTERISTICS Minimum Input Voltage Bias Pin Current 3.2 3.0 2.8 2.6 2.4 –50 –25 0 25 50 75 100 125 150 TEMPERATURE (°C) 30 13 12 11 10 VBIAS = 5V VOUT = 5V fSW = 1MHz 5 15 25 35 45 INPUT VOLTAGE (V) Case Temperature Rise 60 50 15 10 5 65 0 0.2 0.6 1 1.4 1.8 SWITCHING FREQUENCY (MHz) 2.2 8645S-2 G30 Switching Waveforms, Full Frequency Continuous Operation Switch Rising Edge DC2468A DEMO BOARD VIN = 12V, fSW = 500kHz VIN = 24V, fSW = 500kHz VIN = 12V, fSW = 2MHz VIN = 24V, fSW = 2MHz 70 55 20 8645S-2 G29 8645S-2 G28 80 VBIAS = 5V VOUT = 5V VIN = 12V ILOAD = 1A 25 14 BIAS PIN CURRENT (mA) BIAS PIN CURRENT (mA) INPUT VOLTAGE (V) 3.4 CASE TEMPERATURE RISE (°C) Bias Pin Current 15 3.6 IL 1A/DIV VSW 2V/DIV 40 VSW 5V/DIV 30 20 10 0 VIN = 12V ILOAD = 3A 0 1 2 3 4 5 6 LOAD CURRENT (A) 7 2ns/DIV 8645S-2 G32 500ns/DIV 8645S-2 G33 FRONT PAGE APPLICATION 12VIN TO 5VOUT AT 2A 8 8645S-2 G31 Switching Waveforms, Burst Mode Operation IL 500mA/DIV IL 1A/DIV VSW 5V/DIV VSW 20V/DIV 10µs/DIV FRONT PAGE APPLICATION 12VIN TO 5VOUT AT 10mA VSYNC = 0V 8 Transient Response; Internal Switching Waveforms 8645S-2 G34 Compensation Internal Compensation ILOAD 2A/DIV VOUT 100mV/DIV 500ns/DIV FRONT PAGE APPLICATION 48VIN TO 5VOUT AT 2A 8645S-2 G35 20µs/DIV 8645S-2 G36 2A TO 4A TRANSIENT 12VIN, 5VOUT, fSW = 2MHz COUT = 100µF, CLEAD = 4.7pF Rev. A For more information www.analog.com LT8645S-2 TYPICAL PERFORMANCE CHARACTERISTICS Transient Response; 300mA (Burst Mode Operation) to 1.3A Transient to 1.3A Transient ILOAD 1A/DIV VOUT 100mV/DIV 50µs/DIV 8645S-2 G37 300mA TO 1.3A TRANSIENT 12VIN, 5VOUT, fSW = 2MHz COUT = 100µF, CLEAD = 4.7pF Start-Up Dropout Performance VIN 2V/DIV VOUT 2V/DIV VIN VOUT 100ms/DIV 2.5Ω LOAD (2A IN REGULATION) 8645S-2 G38 Start-Up Dropout Performance VIN 2V/DIV VOUT 2V/DIV VIN VOUT 100ms/DIV 20Ω LOAD (250mA IN REGULATION) 8645S-2 G39 Rev. A For more information www.analog.com 9 LT8645S-2 TYPICAL PERFORMANCE CHARACTERISTICS Conducted EMI Performance 60 50 AMPLITUDE (dBµV) 40 30 20 10 0 –10 –20 FIXED FREQUENCY MODE SPREAD SPECTRUM MODE –30 –40 0 3 6 9 12 15 18 FREQUENCY (MHz) DC2468A DEMO BOARD USING LT8645S (WITH EMI FILTER INSTALLED) 14V INPUT TO 5V OUTPUT AT 4A, fSW = 2MHz 21 24 27 30 8645S-2 G40 Radiated EMI Performance (CISPR25 Radiated Emission Test with Class 5 Peak Limits) 50 VERTICAL POLARIZATION PEAK DETECTOR 45 AMPLITUDE (dBµV/m) 40 35 30 25 20 15 10 5 CLASS 5 PEAK LIMIT SPREAD SPECTRUM MODE FIXED FREQUENCY MODE 0 –5 0 100 200 300 400 500 600 FREQUENCY (MHz) 700 800 900 1000 8645S-2 G41 50 HORIZONTAL POLARIZATION PEAK DETECTOR 45 AMPLITUDE (dBµV/m) 40 35 30 25 20 15 10 5 CLASS 5 PEAK LIMIT SPREAD SPECTRUM MODE FIXED FREQUENCY MODE 0 –5 10 0 100 200 300 400 500 600 FREQUENCY (MHz) DC2468A DEMO BOARD USING LT8645S (WITH EMI FILTER INSTALLED) 14V INPUT TO 5V OUTPUT AT 4A, fSW = 2MHz 700 800 900 1000 8645S-2 G42 Rev. A For more information www.analog.com LT8645S-2 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 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 2): Internal 3.4V Regulator Bypass Pin. The internal power drivers and control circuits are powered from this voltage. INTVCC 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. Place a low ESR ceramic capacitor of at least 1µF from this pin to ground close to the IC. NC (Pins 3, 7, 20, 24): No Connect. This pin is not connected to internal circuitry and can be tied anywhere on the PCB, typically ground. VIN (Pins 4, 5, 6, 21, 22, 23): The VIN pins supply current to the LT8645S-2 internal circuitry and to the internal topside power switch. The LT8645S-2 requires the use of multiple VIN bypass capacitors. Two small 0.47µF capacitors should be placed as close as possible to the LT8645S-2, one capacitor on each side of the device (CIN1, CIN2). A third capacitor with a large value, 4.7µF or higher, should be placed near CIN1 or CIN2. 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. Place a 0.1µF boost capacitor as close as possible to the IC. 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-2 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 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 LT8645S-2 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 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. 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 3.1V OR GND VOUT 1.8V 8A 4.7pF 866k FB 1M GND 47µF X2 1210 X5R/X7R 8640S-2 TA02 fSW = 1MHz L: XEL6030 PINS NOT USED IN THIS CIRCUIT: CLKOUT, PG, SYNC/MODE RELATED PARTS PART NUMBER DESCRIPTION COMMENTS 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, 6mm × 4mm LQFN-32 LT8640S/ LT8643S 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 IQ = 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 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 LT8611 42V, 2.5A, 96% Efficiency, 2.2MHz Synchronous MicroPower Step-Down DC/DC Converter with IQ = 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 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 VIN(MIN) = 3.4V, VIN(MAX) = 42V, VOUT(MIN) = 0.97V, DC/DC Converter with IQ = 2.5µA 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 LT8613 42V, 6A, 96% Efficiency, 2.2MHz Synchronous MicroPower Step-Down DC/DC Converter with Current Limiting VIN(MIN) = 3.4V, VIN(MAX) = 42V, VOUT(MIN) = 0.97V, IQ = 3.0μA, ISD < 1μA, 3mm × 6mm QFN-28 LT8602 42V, Quad Output (2.5A + 1.5A + 1.5A + 1.5A) 95% Efficiency, 2.2MHz Synchronous MicroPower Step-Down DC/DC Converter with IQ = 25µA VIN(MIN) = 3V, VIN(MAX) = 42V, VOUT(MIN) = 0.8V, IQ = 2.5μA, ISD < 1μA, 6mm × 6mm QFN-40 30 Rev. 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