LTC1735 High Efficiency Synchronous Step-Down Switching Regulator UFEATURESDESCRIPTIO ■ Synchronizable/Programmable Fixed Frequency The LTC®1735 is a synchronous step-down switching ■ OPTI-LOOPTM Compensation Minimizes C regulator controller that drives external N-channel power OUT ■ ± 1% Output Voltage Accuracy MOSFETs using a fixed frequency architecture. Burst ■ Dual N-Channel MOSFET Synchronous Drive ModeTM operation provides high efficiency at low load ■ Wide V currents. The precision 0.8V reference is compatible with IN Range: 4V to 36V Operation ■ V future generation microprocessors. OPTI-LOOP compen- OUT Range: 0.8V to 6V ■ Internal Current Foldback sation allows the transient response to be optimized over ■ Output Overvoltage Crowbar Protection a wide range of output capacitance and ESR values. ■ Latched Short-Circuit Shutdown Timer The operating frequency (synchronizable up to 500kHz) is with Defeat Option set by an external capacitor allowing maximum flexibility ■ Very Low Dropout Operation: 99% Duty Cycle in optimizing efficiency. A forced continuous control pin ■ Forced Continuous Control Pin reduces noise and RF interference and can assist second- ■ Optional Programmable Soft-Start ary winding regulation by disabling Burst Mode operation ■ Remote Output Voltage Sense when the main output is lightly loaded. ■ Power Good Output (LTC1735F Only) ■ Logic Controlled Micropower Shutdown: I Protection features include internal foldback current lim- Q < 25µA ■ LTC1435 Pin Compatible with iting, output overvoltage crowbar and optional short- Minor Component Changes circuit shutdown. Soft-start is provided by an external ■ Available in 16-Lead Narrow SSOP, SO Packages and capacitor that can be used to properly sequence supplies. 20-Lead TSSOP Package (LTC1735F Only) The operating current level is user-programmable via an U external current sense resistor. Wide input supply range APPLICATIO S allows operation from 4V to 30V (36V maximum). , LTC and LT are registered trademarks of Linear Technology Corporation. ■ Notebook and Palmtop Computers, PDAs Burst Mode and OPTI-LOOP are trademarks of Linear Technology Corporation. ■ Cellular Telephones and Wireless Modems ■ DC Power Distribution Systems UTYPICAL APPLICATIO VIN COSC 5V TO 24V C C SS IN M1 0.1µF C 22µF OSC TG C 47pF B FDS6680A 50V RUN/SS 0.22µF COUT: PANASONIC EEFUEOG181R C BOOST IN: MARCON THCR70E1H226ZT I L1: PANASONIC ETQP6F2R0HFA TH CC RSENSE: IRC LRF2010-01-R005J 330pF SW RC CC2 LTC1735 L1 R 33k SENSE 100pF DB 2µH 0.005Ω VOUT SGND VIN CMDSH-3 1.6V R2 100pF 9A 20k 1% VOSENSE INTVCC + COUT 4.7µF + 180µF R1 M2 D1 4V SENSE– BG 20k FDS6680A MBRS340T3 ×4 1% 1000pF SP SENSE+ PGND 1735 F01 Figure 1. High Efficiency Step-Down Converter 1735fc 1
