LT3641 Dual Monolithic Buck Regulator with Power-On Reset and Watchdog Timer FEATURES DESCRIPTION n High Voltage Buck Regulator: The LT 3641 is a dual channel, current mode monolithic buck 4V to 42V Operating Range switching regulator with a power-on reset and a watchdog 1.3A Output Current timer. Both regulators are synchronized to a single oscillator n Input Transient Protection to 55V with an adjustable frequency (350kHz to 2.5MHz). At light n Low Voltage Synchronous Buck Regulator: loads, both regulators operate in low ripple Burst Mode 2.5V to 5.5V Input Voltage Range to maintain high ef ciency and low output ripple. 1.1A Output Current The high voltage channel is a nonsynchronous buck with n Synchronizable, Adjustable 350kHz to 2.5MHz an internal 2.4A top switch that operates from an input Switching Frequency of 4V to 42V and input transient protection to 55V. The n Programmable Power-On Reset Timer low voltage channel operates from an input of 2.5V to n Programmable Window Mode Watchdog Timer 5.5V. Internal synchronous power switches provide high n Typical Quiescent Current: 290A ef ciency without the need of external Schottky diode. n Short-Circuit Robust Both channels have cycle-by-cycle current limit, providing n Programmable Soft-Start protection against shorted outputs. n Low Shutdown Current: I < 1A Q n The power-on reset and watchdog timeout periods are Thermal Shutdown n both adjustable using external capacitors. The window Available in Thermally Enhanced 28-Lead mode watchdog timer ags when the P pulses group (4mm 5mm) QFN and 28-Lead TSSOP Packages too close together or too far apart. APPLICATIONS The LT3641 is available in a 28-pin 4mm 5mm QFN n Industrial Power Supplies package and 28-pin TSSOP package. Both packages have n Automotive Electronic Control Units an exposed pad for low thermal resistance. L, LT, LTC, LTM, Linear Technology, Burst Mode and the Linear logo are registered trademarks and ThinSOT is a trademark of Linear Technology Corporation. All other trademarks are the property of their respective owners. TYPICAL APPLICATION 2MHz 5V/0.8A and 3.3V/0.5A Step Down Regulators 0.22F HV Channel Ef ciency, LV Channel Ef ciency, V IN 2MHz, V = 5V 2MHz, V = 3.3V OUT1 OUT2 7V TO 42V* 10F 4.7H V OUT1 EN/UVLO V SW BST SW1 90 95 IN 5V/0.8A SYNC 301k 22F DA WDE V = 12V IN V = 5V IN2 FB1 90 PGOOD2 85 100k V OUT1 100k 100k 85 LT3641 V IN2 RST1 80 RST2 EN2 2.2H 80 P WDO V OUT2 SW2 WDI 3.3V/0.5A 75 226k 22F 75 CWDT FB2 CPOR RT GND SS2 SS1 49.9k 70 70 1nF 1.5nF 1.5nF 0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 0 0.2 0.4 0.6 0.8 1.0 1.2 1nF 32.4k V CURRENT (A) V CURRENT (A) OUT1 OUT2 3641 TA01a 3641 TA01b 3641 TA01c * FOR INPUT VOLTAGES ABOVE 42V RESTRICTIONS APPLY 3641fa 1 EFFICIENCY (%) EFFICIENCY (%)LT3641 ABSOLUTE MAXIMUM RATINGS (Note 1) V , EN/UVLO Voltage (Note 7) .................................55V SW2 Voltage ................................ 0.3V to (V + 0.3V) IN IN2 WDE Voltage .............................................................30V Operating Junction Temperature Range (Note 2) BST Above SW, SW1 Voltage ....................... 0.3V to 6V LT3641E ................................................. 40C to 125C SW1 Above SW Voltage ............................... 0.3V to 6V LT3641I .................................................. 40C to 125C V , SYNC, EN2, PGOOD2, WDI, LT3641H ................................................. 40C to 150C IN2 WDO, RST1, RST2, Voltages ....................... 0.3V to 6V Storage Temperature Range ................... 65C to 150C SS1, SS2, FB1, FB2, RT, CWDT, Lead Temperature, FE Only (Soldering, 10 sec) .... 300C CPOR Voltages............................ 0.3V to 2.5V PIN CONFIGURATION TOP VIEW TOP VIEW 1 28 SS2 FB2 2 27 EN2 PGOOD2 3 26 GND EN/UVLO 28 27 26 25 24 23 4 25 SW2 SYNC SYNC 1 22 SW2 5 24 V SS1 IN2 SS1 2 21 V IN2 6 23 GND FB1 FB1 3 20 GND 7 22 V RT IN 29 RT 4 19 V 29 IN GND 8 21 BST GND RST2 RST2 5 18 BST 9 20 SW RST1 RST1 6 17 SW 10 19 SW1 WDO WDO 7 16 SW1 11 18 DA CWDT 8 15 DA CWDT 9 10 11 12 13 14 12 17 NC CPOR 13 16 GND WDE 14 15 GND WDI UFD PACKAGE 28-LEAD (4mm 5mm) PLASTIC QFN FE PACKAGE = 43C/W, = 3.4C/W 28-LEAD PLASTIC TSSOP JA JC EXPOSED PAD (PIN 29) IS GND, MUST BE SOLDERED TO PCB = 30C/W, = 8C/W JA JC EXPOSED PAD (PIN 29) IS GND, MUST BE SOLDERED TO PCB ORDER INFORMATION LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE LT3641EFE PBF LT3641EFE TRPBF LT3641FE 28-Lead Plastic TSSOP 40C to 125C LT3641IFE PBF LT3641IFE TRPBF LT3641FE 28-Lead Plastic TSSOP 40C to 125C LT3641HFE PBF LT3641HFE TRPBF LT3641FE 28-Lead Plastic TSSOP 40C to 150C LT3641EUFD PBF LT3641EUFD TRPBF 3641 40C to 125C 28-Lead (4mm 5mm) Plastic QFN LT3641IUFD PBF LT3641IUFD TRPBF 3641 28-Lead (4mm 5mm) Plastic QFN 40C to 125C Consult LTC Marketing for parts speci ed with wider operating temperature ranges. *The temperature grade is identi ed by a label on the shipping container. 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