LTC1625 No R TM SENSE Current Mode Synchronous Step-Down Switching Regulator UFEATURESDESCRIPTION ■ Highest Efficiency Current Mode Controller The LTC®1625 is a synchronous step-down switching ■ No Sense Resistor Required regulator controller that drives external N-Channel power ■ Stable High Current Operation MOSFETs using few external components. Current mode ■ Dual N-Channel MOSFET Synchronous Drive control with MOSFET VDS sensing eliminates the need for ■ Wide VIN Range: 3.7V to 36V a sense resistor and improves efficiency. The frequency of ■ Wide VOUT Range: 1.19V to VIN a nominal 150kHz internal oscillator can be synchronized ■ ±1% 1.19V Reference to an external clock over a 1.5:1 frequency range. ■ Programmable Fixed Frequency with Injection Lock Burst ModeTM operation at low load currents reduces ■ Very Low Drop Out Operation: 99% Duty Cycle switching losses and low dropout operation extends oper- ■ Forced Continuous Mode Control Pin ating time in battery-powered systems. A forced continu- ■ Optional Programmable Soft Start ous mode control pin can assist secondary winding ■ Pin Selectable Output Voltage regulation by disabling Burst Mode operation when the ■ Foldback Current Limit main output is lightly loaded. ■ Output Overvoltage Protection ■ Logic Controlled Micropower Shutdown: I Fault protection is provided by foldback current limiting Q < 30µA ■ Available in 16-Lead Narrow SSOP and SO Packages and an output overvoltage comparator. An external ca- pacitor attached to the RUN/SS pin provides soft start U capability for supply sequencing. A wide supply range APPLICATIONS allows operation from 3.7V (3.9V for LTC1625I) to 36V at the input and 1.19V to V ■ IN at the output. Notebook and Palmtop Computers, PDAs ■ Cellular Telephones and Wireless Modems , LTC and LT are registered trademarks of Linear Technology Corporation. No RSENSE and Burst Mode are trademarks of Linear Technology Corporation. ■ Battery Chargers ■ Distributed Power UTYPICAL APPLICATIONEfficiency vs Load Current 100 VIN VIN = 10V SYNC V V IN 5V TO OUT = 5V + CIN RUN/SS TK 28V 10µF CSS M1 90 0.1µF TG 30V Si4410DY L1 LTC1625 ×2 VOUT = 3.3V 10µH I SW V TH OUT CB 0.22µF 3.3V RC BOOST + COUT 4.5A 80 10k D D1 B 100µF CMDSH-3 MBRS140T3 CVCC 4.7µF 10V C EFFICIENCY (%) C V INTV PROG CC + ×3 2.2nF M2 70 SGND BG Si4410DY VOSENSE PGND 1625 F01 60 0.01 0.1 1 10 LOAD CURRENT (A) Figure 1. High Efficiency Step-Down Converter 1625 TA01 1
