POWER LOSS (mW) LTC3851 Synchronous Step-Down Switching Regulator Controller FEATURES DESCRIPTION n Wide V Range: 4V to 38V Operation The LTC 3851 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 con stant frequency current mode architecture 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 LTC3851 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 allows Thermally Enhanced 16-Lead MSOP, 16-Lead Narrow the IC to be synchronized to an external clock. SSOP or 3mm 3mm QFN Package The LTC3851-1 is a version with a power good output signal instead of adjustable current limit. APPLICATIONS L, LT, LTC, LTM, Burst Mode and OPTI-LOOP are registered trademarks of Linear Technology n Automotive Systems Corporation. All other trademarks are the property of their respective owners. Protected by U.S. Patents including 5408150, 5481178, 5705919, 5929620, 6304066, 6498466, 6580258, n Telecom Systems 6611131. n Industrial Equipment n Distributed DC Power Systems TYPICAL APPLICATION High Ef ciency Synchronous Step-Down Converter Ef ciency 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 LTC3851 0.1F 15A EFFICIENCY 85 BOOST TK/SS 1000 330F 0.1F 3.01k s 2 80 75 INTV POWER LOSS CC 2200pF 4.7F 70 BG I TH 100 65 GND 15k 330pF 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 3851TA01b 3851 TA01a 3851fb 1 EFFICIENCY (%)LTC3851 ABSOLUTE MAXIMUM RATINGS (Note 1) Input Supply Voltage (V ) ......................... 40V to 0.3V I , V Voltages .......................................... 3V to 0.3V IN TH FB Topside Driver Voltage (BOOST) ................ 46V to 0.3V INTV Peak Output Current ..................................50mA CC Switch Voltage (SW) ..................................... 40V to 5V Operating Temperature Range (Note 2)..40C to 125C INTV , (BOOST SW), RUN ...................... 6V to 0.3V Junction Temperature (Note 3) ............................. 125C CC TK/SS, I ............................................ INTV to 0.3V Storage Temperature Range ...................65C to 150C LIM CC + SENSE , SENSE .......................................... 6V to 0.3V Lead Temperature (Soldering, 10 sec) MODE/PLLIN, FREQ/PLLFLTR ............... INTV to 0.3V GN/MSE ............................................................300C CC PIN CONFIGURATION TOP VIEW TOP VIEW TOP VIEW MODE/PLLIN 1 16 SW 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 13 V IN 17 TK/SS 4 13 V TK/SS 2 11 V 5 IN IN I 12 INTV TH CC 17 FB 6 11 BG I 3 10 INTV I 5 12 INTV TH CC TH CC 7 SENSE 10 GND + SENSE 8 9 I FB BG 4 9 FB 6 11 BG LIM MSE PACKAGE 5 6 7 8 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 s 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 ORDER INFORMATION LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE LTC3851EGN PBF LTC3851EGN TRPBF 3851 16-Lead Plastic SSOP 40C to 85C LTC3851IGN PBF LTC3851IGN TRPBF 3851 16-Lead Plastic SSOP 40C to 125C LTC3851EMSE PBF LTC3851EMSE TRPBF 3851 16-Lead Plastic MSOP 40C to 85C LTC3851IMSE PBF LTC3851IMSE TRPBF 3851 16-Lead Plastic MSOP 40C to 125C LTC3851EUD PBF LTC3851EUD TRPBF LCXN 40C to 85C 16-Lead (3mm 3mm) Plastic QFN LTC3851IUD PBF LTC3851IUD TRPBF LCXN 40C to 125C 16-Lead (3mm 3mm) Plastic QFN 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: