POWER LOSS (W) LTC3852 Low Input Voltage, Synchronous Step-Down DC/DC Controller FEATURES DESCRIPTION n Charge Pump Input Range: 2.7V to 5.5V The LTC 3852 is a constant frequency, current mode n Controller Input Range: 4V to 38V step-down DC/DC controller which can be powered by an n Integrated Charge Pump Provides 5V Gate Drive to onboard charge pump. Input supplies as low as 2.7V, when Logic Level MOSFETs doubled by the charge pump, provide 5V to the LTC3852s n R or DCR Current Sensing control logic and gate drives, supporting a wide selection SENSE n 1.25% Output Voltage Accuracy Over Temperature of logic-level N-channel power MOSFETs. n Phase-Lockable Fixed Frequency: 250kHz to 750kHz The constant-frequency current mode architecture allows for n Power Good Output Voltage Monitor a phase-lockable xed frequency of up to 750kHz. The RUN n Adjustable Soft-Start Voltage Ramping pin provides a precision enable threshold while the TRACK/SS n Current Foldback Disabled During Start-Up pin combines tracking and adjustable soft-start features. n No Reverse Current During Soft-Start n The MODE/PLLIN pin selects among Burst Mode oper- Selectable Constant Frequency, Pulse-Skipping, or ation, pulse-skipping mode, and continuous current mode. Burst Mode Operation n Current foldback limits MOSFET power dissipation during Output Overvoltage Protection n short-circuit conditions. Reverse current and current Very Low Dropout Operation: 99% Duty Cycle n foldback functions are disabled during soft-start. A power Available in a 24-Lead (3mm 5mm) QFN Package good output pin indicates when the output is within 10% APPLICATIONS of its designed set point. L, LT, LTC, LTM, Linear Technology, Burst Mode and the Linear logo are registered trademarks n General Purpose 3.3V Systems and No R is a trademark of Linear Technology Corporation. All other trademarks are the SENSE property of their respective owners. Protected by U.S. Patents including 5408150, 5481178, n Lithium-Ion Powered Devices 5705919, 6498466, 6580258, 6611131. n Distributed DC Power Systems TYPICAL APPLICATION High Ef ciency Synchronous Step-Down Converter Ef ciency and Power Loss vs Load Current 100k V IN PGO0D INTV V CC IN1 2.7V TO 5.5V 100 5 22F TG MODE/PLLIN 90 0.36H 4.5 V OUT EFFICIENCY FREQ/PLLFLTR SW 1.2V 80 4 0.1F 20A 95.3k BOOST 70 3.5 470F TRACK/SS 2.1k V 2 IN2 60 3 0.1F INTV 1nF CC 50 2.5 4.7F LTC3852 I BG 40 TH 2 GND2 30 1.5 12.1k 100pF POWER LOSS + 20k 20 1 RUN SENSE 1% 0.1F OFF ON 10 0.5 SHDN SENSE + 0 0 CHARGE PUMP V C FB 12100 2.2F 40.2k V C PUMP GND1 LOAD CURRENT (A) 1% 3852 TA01 3852 TA01a 3852f 1 EFFICIENCY (%) +LTC3852 ABSOLUTE MAXIMUM RATINGS PIN CONFIGURATION (Note 1) TOP VIEW Input Supply Voltage (V ) .........................6V to 0.3V IN1 Top Side Driver Voltage (BOOST) ...............46V to 0.3V Switch Voltage (SW) ..................................40V to 0.3V 24 23 22 21 V .......................................................5.5V to 0.3V PUMP SHDN, RUN ..................................................6V to 0.3V SENSE 1 20 FREQ/PLLFLTR + V Short-Circuit Duration .......................... Inde nite PUMP SENSE 2 19 MODE/PLLIN V ............................................................40V to 0.3V PGOOD 3 18 SW IN2 INTV , (BOOST-SW), RUN, PGOOD ...........6V to 0.3V GND2 4 17 TG CC 25 GND BG BOOST 5 16 INTV , Peak Output Current .................................50mA CC + NC 6 15 V IN2 SENSE , SENSE ..........................................6V to 0.3V + C 7 14 INTV CC MODE/PLLIN, TRACK/SS .....................INTV to 0.3V CC C 8 13 V PUMP FREQ/PLLFLTR .....................................INTV to 0.3V CC I , V ........................................................3V to 0.3V TH FB 910 11 12 Operating Junction Temperature (Note 2) ............. 125C Storage Temperature Range .................. 65C to 125C UDD PACKAGE 24-LEAD (3mm s 5mm ) PLASTIC QFN T = 125C, q = 38C/W JMAX JA EXPOSED PAD (PIN 25) IS GND, MUST BE SOLDERED TO PCB ORDER INFORMATION LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE LTC3852EUDD PBF LTC3852EUDD TRPBF LFRJ 40C to 125C 24-Lead (3mm 5mm) Plastic QFN LTC3852IUDD PBF LTC3852IUDD TRPBF LFRJ 40C to 125C 24-Lead (3mm 5mm) 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. For more information on lead free part marking, go to: