POWER LOSS (mW) LTC3851A-1 Synchronous Step-Down Switching Regulator Controller Fea T Descrip T n Wide V Range: 4V to 38V Operation The LTC 3851A-1 is a high performance synchronous IN n R or DCR Current Sensing step-down switching regulator controller that drives SENSE n 1% Output Voltage Accuracy an all N-channel synchronous power MOSFET stage. A n Power Good Output Voltage Monitor con stant frequency current mode architecture allows a n Phase-Lockable Fixed Frequency: 250kHz to 750kHz phase-lockable frequency of up to 750kHz. n Dual N-Channel MOSFET Synchronous Drive OPTI-LOOP compensation allows the transient response n Very Low Dropout Operation: 99% Duty Cycle to be optimized over a wide range of output capacitance n Adjustable Output Voltage Soft-Start or Tracking and ESR values. The LTC3851A-1 features a precision 0.8V n Output Current Foldback Limiting reference and a power good indicator. A wide 4V to 38V n Output Overvoltage Protection (40V absolute maximum) input supply range encompasses n OPTI-LOOP Compensation Minimizes C OUT most battery configurations and intermediate bus voltages. n Selectable Continuous, Pulse-Skipping or The TK/SS pin ramps the output voltage during start-up and Burst Mode Operation at Light Loads n shutdown with coincident or ratiometric tracking. Current Low Shutdown I : 20A Q n foldback limits MOSFET heat dissipation during short- V Range: 0.8V to 5.5V OUT n circuit conditions. The MODE/PLLIN pin selects among Thermally Enhanced 16-Lead MSOP Burst Mode operation, pulse-skipping mode or continu- or 3mm 3mm QFN Package ous inductor current mode at light loads and allows the IC to be synchronized to an external clock. The LTC3851A-1 a T contains an improved PLL compared to the LTC3851-1. n Automotive Systems The LTC3851A-1 is identical to the LTC3851A except that n Telecom Systems pin is replaced by PGOOD. the I LIM n Industrial Equipment L, LT, LTC, LTM, Burst Mode, OPTI-LOOP, Linear Technology and the Linear logo are registered n trademarks and No R , UltraFast are trademarks of Linear Technology Corporation. All other SENSE Distributed DC Power Systems trademarks are the property of their respective owners. Protected by U.S. Patents including 5408150, 5481178, 5705919, 5929620, 6304066, 6498466, 6580258, 6611131. Typical a T Efficiency and Power Loss High Efficiency Synchronous Step-Down Converter vs Load Current 100k V IN 100 10000 PGO0D INTV V CC IN 4.5V TO 38V V = 12V IN 22F 95 V = 3.3V OUT FREQ/PLLFLTR TG 0.68H V EFFICIENCY OUT 0.1F 82.5k 90 RUN SW 3.3V LTC3851A-1 0.1F 15A 85 1000 TK/SS BOOST 330F 80 0.1F 3.01k 2 POWER LOSS 75 INTV CC 2200pF 4.7F 70 BG 100 I TH 65 GND 15k 330pF 60 + SENSE 55 MODE/PLLIN 0.047F 30.1k 50 10 154k 10 100 1000 10000 100000 SENSE V LOAD CURRENT (mA) FB 3851A1 TA01b 48.7k 3851A1 TA01a 3851a1fa 1 EFFICIENCY (%) ion pplica ions pplica ion uresLTC3851A-1 a Te Maxi Mu M r a T (Note 1) Input Supply Voltage (V ) ......................... 40V to 0.3V INTV Peak Output Current ..................................50mA IN CC Topside Driver Voltage (BOOST) ................ 46V to 0.3V Operating Junction Temperature Range (Notes 2, 3) Switch Voltage (SW) .....................................40V to 5V E-Grade, I-Grade ................................ 40C to 125C INTV , (BOOST SW), RUN, PGOOD ........ 6V to 0.3V H-Grade ............................................. 40C to 150C CC TK/SS ...................................................INTV to 0.3V MP-Grade .......................................... 55C to 150C CC + SENSE , SENSE .......................................... 6V to 0.3V Storage Temperature Range ..................65C to 150C MODE/PLLIN, FREQ/PLLFLTR ..............INTV to 0.3V Lead Temperature (Soldering, 10 sec) CC I , V Voltages ......................................... 3V to 0.3V MSE ..................................................................300C TH FB p in c F T TOP VIEW TOP VIEW MODE/PLLIN 1 16 SW 16 15 14 13 FREQ/PLLFLTR 2 15 TG RUN 3 14 BOOST RUN 1 12 BOOST TK/SS 4 17 13 V IN I 5 GND 12 INTV TK/SS 2 11 V TH CC IN 17 FB 6 11 BG GND I 3 10 INTV TH CC SENSE 7 10 GND + SENSE 8 9 PGOOD FB BG 4 9 MSE PACKAGE 5 6 7 8 16-LEAD PLASTIC MSOP T = 125C, = 35C/W TO 40C/W JMAX JA EXPOSED PAD (PIN 17) IS GND, MUST BE SOLDERED TO PCB UD PACKAGE 16-LEAD (3mm 3mm) PLASTIC QFN T = 125C, = 68C/W, = 4.2C/W JMAX JA JC EXPOSED PAD (PIN 17) IS GND, MUST BE SOLDERED TO PCB o r Der i n F Ma T LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE LTC3851AEMSE-1 PBF LTC3851AEMSE-1 TRPBF 3851A1 16-Lead Plastic MSOP 40C to 125C LTC3851AIMSE-1 PBF LTC3851AIMSE-1 TRPBF 3851A1 16-Lead Plastic MSOP 40C to 125C LTC3851AHMSE-1 PBF LTC3851AHMSE-1 TRPBF 3851A1 16-Lead Plastic MSOP 40C to 150C LTC3851AMPMSE-1 PBF LTC3851AMPMSE-1 TRPBF 3851A1 16-Lead Plastic MSOP 55C to 150C LTC3851AEUD-1 PBF LTC3851AEUD-1 TRPBF LFQB 16-Lead (3mm 3mm) Plastic QFN 40C to 125C LTC3851AIUD-1 PBF LTC3851AIUD-1 TRPBF LFQB 16-Lead (3mm 3mm) Plastic QFN 40C to 125C Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container. Consult LTC Marketing for information on non-standard lead based finish parts. For more information on lead free part marking, go to: