POWER LOSS (mW) LTC3851-1 Synchronous Step-Down Switching Regulator Controller FEATURES DESCRIPTION n Wide V Range: 4V to 38V Operation The LTC 3851-1 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 LTC3851-1 features a precision 0.8V n Output Current Foldback Limiting reference and a power good indicator. A wide 4V to 38V (40V n Output Overvoltage Protection absolute maximum) input supply range encompasses most n OPTI-LOOP Compensation Minimizes C OUT battery con gurations and intermediate bus voltages. n Selectable Continuous, Pulse-Skipping or The TK/SS pin ramps the output voltage during start-up Burst Mode Operation at Light Loads n and shutdown with coincident or ratiometric tracking. Low Shutdown I : 20A Q n Current foldback limits MOSFET heat dissipation during V Range: 0.8V to 5.5V OUT n short-circuit conditions. The MODE/PLLIN pin selects Thermally Enhanced 16-Lead MSOP among Burst Mode operation, pulse skipping mode or or 3mm 3mm QFN Package continuous inductor current mode at light loads and allows APPLICATIONS the IC to be synchronized to an external clock. n Automotive Systems The LTC3851-1 is identical to the LTC3851 except that the n Telecom Systems I pin is replaced by PGOOD. LIM n Industrial Equipment L, LT, LTC, LTM, Burst Mode and OPTI-LOOP are registered trademarks of Linear Technology n Corporation. All other trademarks are the property of their respective owners. Distributed DC Power Systems Protected by U.S. Patents including 5408150, 5481178, 5705919, 5929620, 6304066, 6498466, 6580258, 6611131. TYPICAL APPLICATION High Ef ciency Synchronous Step-Down Converter Ef ciency and Power Loss vs Load Current 100k V IN INTV PGO0D V CC IN 4.5V TO 38V 100 10000 22F TG V = 12V FREQ/PLLFLTR IN 0.68H V 95 OUT V = 3.3V 0.1F OUT 82.5k RUN SW 3.3V EFFICIENCY 90 LTC3851-1 0.1F 15A TK/SS BOOST 330F 85 1000 0.1F 3.01k s 2 80 POWER LOSS INTV CC 75 2200pF 4.7F BG I 70 TH 100 GND 65 15k 330pF + 60 SENSE MODE/PLLIN 0.047F 30.1k 55 154k SENSE 50 10 V FB 10 100 1000 10000 100000 LOAD CURRENT (mA) 48.7k 38511TA01b 38511 TA01a 38511fa 1 EFFICIENCY (%)LTC3851-1 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 Junction Temperature Range INTV , (BOOST SW), RUN, PGOOD ........ 6V to 0.3V (Notes 2, 3) ............................................40C to 125C CC TK/SS .................................................... INTV to 0.3V Storage Temperature Range ...................65C to 150C CC + SENSE , SENSE .......................................... 6V to 0.3V Lead Temperature (Soldering, 10 sec) MODE/PLLIN, FREQ/PLLFLTR ............... INTV to 0.3V MSE ..................................................................300C CC PIN CONFIGURATION 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 4 TK/SS 13 V IN 17 TK/SS 2 11 V I 5 12 INTV IN TH CC 17 6 FB 11 BG I 3 10 INTV TH CC SENSE 7 10 GND + 8 SENSE 9 PGOOD FB 4 9 BG 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 s 3mm) PLASTIC QFN 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 LTC3851EMSE-1 PBF LTC3851EMSE-1 TRPBF 38511 16-Lead Plastic MSOP 40C to 85C LTC3851IMSE-1 PBF LTC3851IMSE-1 TRPBF 38511 16-Lead Plastic MSOP 40C to 125C LTC3851EUD-1 PBF LTC3851EUD-1 TRPBF LDNT 40C to 85C 16-Lead (3mm 3mm) Plastic QFN LTC3851IUD-1 PBF LTC3851IUD-1 TRPBF LDNT 16-Lead (3mm 3mm) 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: