POWER LOSS (mW) LT3688 Dual 800mA Step-Down Switching Regulator with Power-On Reset and Watchdog Timer FEATURES DESCRIPTION n Wide Input Range: The LT 3688 is an adjustable frequency (350kHz to Operation from 3.8V to 36V 2.2MHz) dual monolithic step-down switching regulator n Low Ripple (<25mV ) Burst Mode Operation: with two power-on reset timers and a watchdog timer. P-P I = 115A at 12V to 3.3V and 5V The regulator operates off inputs up to 36V. Low ripple Q IN n Programmable, Defeatable Window Watchdog Timer Burst Mode operation maintains high ef ciency at low n Two Independently Programmable Power-On-Reset output current while keeping output ripple below 25mV in Timers a typical application, with input quiescent current of just n Synchronizable, Adjustable 350kHz-2.2MHz 115A. Shutdown circuitry reduces input supply current Switching Frequency to less than 1A while EN/UVLO is pulled low. n Two 800mA Output Switching Regulators with Internal The reset and watchdog timeout periods are both adjust- Power Switches able using external capacitors. Tight accuracy speci ca- n Programmable Input Undervoltage Lockout with tions and glitch immunity ensure reliable reset operation Hysteresis without false triggering. The open collector RST pins will n Thermally Enhanced 24-Pin TSSOP and 4mm 4mm pull down if the monitored output voltage drops 10% QFN Packages below the programmed value. The LT3688 watchdog timer monitors for watchdog falling edges grouped too close APPLICATIONS together or too far apart. n Automotive Electronic Control Units The LT3688 is available in 24-Pin TSSOP and 4mm n Industrial Power Supplies 4mm QFN packages, each with an exposed pad for low n High-Reliability Processor Systems thermal resistance. L, LT, LTC, LTM, Burst Mode, Linear Technology and the Linear logo are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. TYPICAL APPLICATION 5V and 3.3V Regulator with Power-On Reset and Watchdog Timers Ef ciency V 90 10000.0 IN V = 12V IN 6V TO 36V V = 3.3V 4.7F OUT EN/UVLO V BIAS IN L = 4.7H 80 1000.0 f = 800kHz BST1 BST2 18H 0.22F 0.22F 12H V V OUT1 OUT2 70 100.0 5V 3.3V SW1 SW2 800mA 800mA LT3688 523k 316k 60 10.0 22pF DA1 DA2 22pF FB1 FB2 1nF 1nF 50 1.0 22F 100k 100k 22F RUN/SS2 RUN/SS1 40 0.1 C WDT P I/O WDI C POR1 1nF I/O WDO 30 0.01 C POR2 RESET RST1 0.0001 0.001 0.01 0.1 1 4.7nF RT RST2 4.7nF LOAD CURRENT (A) SYNC GND 3688 TA01b 110k 3688 TA01a f = 500kHz SW 3688f 1 EFFICIENCY (%)LT3688 ABSOLUTE MAXIMUM RATINGS (Note 1) V , EN/UVLO, CONFIG Voltage (Note 2) ...................36V Operating Junction Temperature Range (Note 3) IN BST Voltage ..............................................................55V LT3688E, LT3688I ..............................40C to 125C BST above SW Voltage .............................................30V LT3688H ............................................40C to 150C BIAS Voltage .............................................................30V Maximum Junction Temperature WDE, WDI, RST, WDO Voltage ...................................6V LT3688E, LT3688I .............................................125C FB, RT, SYNC, RUN/SS Voltage ..................................6V LT3688H ...........................................................150C C , C Voltage ....................................................3V Storage Temperature Range ...................65C to 150C WDT POR Lead Temperature (Soldering, 10 sec) FE Package .......................................................300C PIN CONFIGURATION TOP VIEW TOP VIEW FB1 1 24 EN/UVLO RUN/SS1 2 23 SYNC 24 23 22 21 20 19 BST1 3 22 RT RT 1 18 WDO SW1 4 21 C WDT SYNC RST1 2 17 DA1 5 20 C POR1 EN/UVLO 3 16 RST2 V 6 19 BIAS 25 25 IN GND GND FB1 4 15 FB2 CONFIG 7 18 C POR2 RUN/SS1 5 14 RUN/SS2 DA2 8 17 WDI BST1 6 13 BST2 SW2 9 16 WDE 7 8 9 10 11 12 BST2 10 15 WDO RUN/SS2 11 14 RST1 FB2 12 13 RST2 UF PACKAGE FE PACKAGE 24-LEAD PLASTIC TSSOP 24-LEAD (4mm 4mm) PLASTIC QFN = 38C/W = 37C/W JA JA EXPOSED PAD (PIN 25) IS GND, MUST BE ELECTRICALLY CONNECTED TO PCB EXPOSED PAD (PIN 25) IS GND, MUST BE ELECTRICALLY CONNECTED TO PCB ORDER INFORMATION LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE LT3688EFE PBF LT3688EFE TRPBF LT3688FE 24-Lead Plastic TSSOP 40C to 125C LT3688IFE PBF LT3688IFE TRPBF LT3688FE 24-Lead Plastic TSSOP 40C to 125C LT3688HFE PBF LT3688HFE TRPBF LT3688FE 24-Lead Plastic TSSOP 40C to 150C LT3688EUF PBF LT3688EUF TRPBF 3688 24-Lead (4mm 4mm) Plastic QFN 40C to 125C LT3688IUF PBF LT3688IUF TRPBF 3688 24-Lead (4mm 4mm) 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. Consult LTC Marketing for information on non-standard lead based nish parts. For more information on lead free part marking, go to: