POWER LOSS (mW) LTC3851A Synchronous Step-Down Switching Regulator Controller Fea T Descrip T n Wide V Range: 4V to 38V Operation The LTC 3851A 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 Phase-Lockable Fixed Frequency: 250kHz to 750kHz constant frequency current mode ar chitecture allows a n Dual N-Channel MOSFET Synchronous Drive phase-lockable frequency of up to 750kHz. n Very Low Dropout Operation: 99% Duty Cycle OPTI-LOOP compensation allows the transient response n Adjustable Output Voltage Soft-Start or Tracking to be optimized over a wide range of output capacitance n Output Current Foldback Limiting and ESR values. The LTC3851A features a precision 0.8V n Output Overvoltage Protection reference that is compatible with a wide 4V to 38V input n 5V Internal Regulator supply range. n OPTI-LOOP Compensation Minimizes C OUT n The TK/SS pin ramps the output voltage during start-up. Selectable Continuous, Pulse-Skipping or Current foldback limits MOSFET heat dissipation during Burst Mode Operation at Light Loads n short-circuit conditions. The MODE/PLLIN pin selects Low Shutdown I : 20A Q n among Burst Mode operation, pulse-skipping mode or V Range: 0.8V to 5.5V OUT n continuous inductor current mode at light loads and al- Thermally Enhanced 16-Lead MSOP, 16-Lead Narrow lows the IC to be synchronized to an external clock. The SSOP or 3mm 3mm QFN Package LTC3851A contains an improved PLL compared to the a T LTC3851. n Automotive Systems The LTC3851A-1 is a version with a power good output n Telecom Systems signal instead of adjustable current limit. n Industrial Equipment L, LT, LTC, LTM, Burst Mode, OPTI-LOOP, Linear Technology and the Linear logo are registered trademarks and No R , UltraFast are trademarks of Linear Technology Corporation. All other SENSE n 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 High Efficiency Synchronous Step-Down Converter Efficiency and Power Loss vs Load Current V IN I V LIM IN 100 10000 4.5V TO 36V 22F V = 12V IN FREQ/PLLFLTR TG 95 V = 3.3V OUT 0.68H V OUT 0.1F 82.5k RUN SW 3.3V 90 EFFICIENCY LTC3851A 0.1F 15A 85 TK/SS BOOST 1000 330F 0.1F 3.01k 80 2 75 POWER LOSS INTV CC 2200pF 4.7F 70 BG I TH 100 65 GND 330pF 15k 60 + SENSE 55 MODE/PLLIN 0.047F 30.1k 154k 50 10 SENSE 10 100 1000 10000 100000 V FB LOAD CURRENT (mA) 48.7k 3851A TA01b 3851A TA01a 3851afa 1 EFFICIENCY (%) ion pplica ions pplica ion uresLTC3851A 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 ...................... 6V to 0.3V H-Grade ............................................. 40C to 150C CC TK/SS, I ...........................................INTV to 0.3V MP-Grade .......................................... 55C to 150C LIM 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 GN/MSE ............................................................300C TH FB p in c F T TOP VIEW TOP VIEW MODE/PLLIN 1 16 SW TOP VIEW MODE/PLLIN 1 16 SW FREQ/PLLFLTR 2 15 TG 16 15 14 13 FREQ/PLLFLTR 2 15 TG RUN 3 14 BOOST RUN 3 14 BOOST RUN 1 12 BOOST TK/SS 4 17 13 V IN TK/SS 4 13 V TK/SS 2 11 V IN I 5 12 INTV 17 IN GND TH CC FB 6 11 BG GND I 3 10 INTV I 5 12 INTV TH CC TH CC SENSE 7 10 GND + FB BG SENSE 8 9 I 4 9 FB 6 11 BG LIM 5 6 7 8 MSE PACKAGE SENSE 7 10 GND 16-LEAD PLASTIC MSOP + SENSE 8 9 I LIM T = 125C, = 35C/W TO 40C/W JMAX JA EXPOSED PAD (PIN 17) IS GND, GN PACKAGE UD PACKAGE MUST BE SOLDERED TO PCB 16-LEAD PLASTIC SSOP NARROW 16-LEAD (3mm 3mm) PLASTIC QFN T = 125C, = 110C/W JMAX JA 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 LTC3851AEGN PBF LTC3851AEGN TRPBF 3851A 16-Lead Plastic SSOP 40C to 125C LTC3851AIGN PBF LTC3851AIGN TRPBF 3851A 16-Lead Plastic SSOP 40C to 125C LTC3851AEMSE PBF LTC3851AEMSE TRPBF 3851A 16-Lead Plastic MSOP 40C to 125C LTC3851AIMSE PBF LTC3851AIMSE TRPBF 3851A 16-Lead Plastic MSOP 40C to 125C LTC3851AHMSE PBF LTC3851AHMSE TRPBF 3851A 16-Lead Plastic MSOP 40C to 150C LTC3851AMPMSE PBF LTC3851AMPMSE TRPBF 3851A 16-Lead Plastic MSOP 55C to 150C LTC3851AEUD PBF LTC3851AEUD TRPBF LFPZ 16-Lead (3mm 3mm) Plastic QFN 40C to 125C LTC3851AIUD PBF LTC3851AIUD TRPBF LFPZ 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: