LTC1435 High Efficiency Low Noise Synchronous Step-Down Switching Regulator DESCRIPTION FEATURES n Dual N-Channel MOSFET Synchronous Drive The LTC 1435 is a synchronous step-down switching n Programmable Fixed Frequency regulator controller that drives external N-channel power n Wide V Range: 3.5V to 36V Operation MOSFETs using a fixed frequency architecture. Burst IN TM n Ultrahigh Efficiency Mode operation provides high efficiency at low load n Very Low Dropout Operation: 99% Duty Cycle currents. A maximum duty cycle limit of 99% provides low n Low Standby Current dropout operation which extends operating time in bat- n Secondary Feedback Control tery-operated systems. n Programmable Soft Start The operating frequency is set by an external capacitor n Remote Output Voltage Sense allowing maximum flexibility in optimizing efficiency. A n Logic Controlled Micropower Shutdown: I < 25A Q secondary winding feedback control pin, SFB, guarantees n Foldback Current Limiting (Optional) regulation regardless of load on the main output by n Current Mode Operation for Excellent Line and Load forcing continuous operation. Burst Mode operation is Transient Response inhibited when the SFB pin is pulled low which reduces n Output Voltages from 1.19V to 9V noise and RF interference. n Available in 16-Lead Narrow SO and SSOP Packages Soft start is provided by an external capacitor which can U APPLICATIONS be used to properly sequence supplies. The operating current level is user-programmable via an external current n Notebook and Palmtop Computers, PDAs sense resistor. Wide input supply range allows operation n Cellular Telephones and Wireless Modems from 3.5V to 30V (36V maximum). n Portable Instruments , LTC and LT are registered trademarks of Linear Technology Corporation. n Battery-Operated Devices Burst Mode is a trademark of Linear Technology Corporation. n DC Power Distribution Systems TYPICAL APPLICATION V IN 4.5V TO 28V C V OSC IN C IN + C OSC M1 22F RUN/SS TG 68pF Si4412DY 35V C R SS SENSE 2 0.1F 0.033 V OUT I SW TH 2.9V/3.5A L1 C D C B LTC1435 10H 330pF CMDSH-3 R1 R C C INTV OUT C B 32.4k CC 10k 0.1F 100F 10V SGND BOOST R2 2 + D1 22.1k 100pF 4.7F MBRS140T3 M2 V BG Si4412DY OSENSE PGND + SENSE SENSE 1000pF 1435 F01 Figure 1. High Efficiency Step-Down Converter 1 + U ULTC1435 ABSOLUTE MAXIMUM RATINGS PACKAGE/ORDER INFORMATION Input Supply Voltage (V ).........................36V to 0.3V IN TOP VIEW ORDER PART Topside Driver Supply Voltage (Boost) ......42V to 0.3V NUMBER C 1 16 TG OSC Switch Voltage (SW)............................. V + 5V to 5V IN RUN/SS 2 15 BOOST EXTV Voltage ........................................ 10V to 0.3V CC LTC1435CG I 3 14 SW TH + Sense , Sense Voltages ......... INTV + 0.3V to 0.3V CC LTC1435CS SFB 4 13 V IN I , V Voltages .............................. 2.7V to 0.3V TH OSENSE LTC1435IG SGND 5 12 INTV CC SFB, Run/SS Voltages .............................. 10V to 0.3V LTC1435IS V 6 11 BG OSENSE Peak Driver Output Current < 10s (TG, BG) ............. 2A SENSE 7 10 PGND + INTV Output Current ........................................ 50mA SENSE 8 9 EXTV CC CC Operating Ambient Temperature Range G PACKAGE S PACKAGE 16-LEAD PLASTIC SSOP 16-LEAD PLASTIC SO LTC1435C............................................... 0C to 70C T = 125C, = 130C/ W (G) LTC1435I............................................ 40C to 85C JMAX JA T = 125C, = 110C/ W (S) JMAX JA Junction Temperature (Note 1)............................. 125C Storage Temperature Range ................. 65C to 150C Consult factory for Military grade parts. Lead Temperature (Soldering, 10 sec).................. 300C ELECTRICAL CHARACTERISTICS T = 25C, V = 15V, V = 5V unless otherwise noted. A IN RUN/SS SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS Main Control Loop I V Feedback Current (Note 2) 10 50 nA IN OSENSE V Feedback Voltage (Note 2) l 1.178 1.19 1.202 V OSENSE V Reference Voltage Line Regulation V = 3.6V to 20V (Note 2) 0.002 0.01 %/V LINEREG IN V Output Voltage Load Regulation I Sinking 5A (Note 2) l 0.5 0.8 % LOADREG TH I Sourcing 5A l 0.5 0.8 % TH V Secondary Feedback Threshold V Ramping Negative l 1.16 1.19 1.22 V SFB SFB I Secondary Feedback Current V = 1.5V 1 2 A SFB SFB V Output Overvoltage Lockout 1.24 1.28 1.32 V OVL I Input DC Supply Current EXTV = 5V (Note 3) Q CC Normal Mode 3.6V < V < 30V 260 A IN Shutdown V = 0V, 3.6V < V < 15V 16 25 A RUN/SS IN V Run Pin Threshold l 0.8 1.3 2 V RUN/SS I Soft Start Current Source V = 0V 1.5 3 4.5 A RUN/SS RUN/SS V Maximum Current Sense Threshold V = 0V, 5V 130 150 180 mV SENSE(MAX) OSENSE TG Transition Time TG t Rise Time C = 3000pF 50 150 ns r LOAD TG t Fall Time C = 3000pF 50 150 ns f LOAD BG Transition Time BG t Rise Time C = 3000pF 50 150 ns r LOAD BG t Fall Time C = 3000pF 40 150 ns f LOAD Internal V Regulator CC V Internal V Voltage 6V < V < 30V, V = 4V l 4.8 5.0 5.2 V INTVCC CC IN EXTVCC V INT INTV Load Regulation I = 15mA, V = 4V 0.2 1 % LDO CC INTVCC EXTVCC V EXT EXTV Voltage Drop I = 15mA, V = 5V 130 230 mV LDO CC INTVCC EXTVCC V EXTV Switchover Voltage I = 15mA, V Ramping Positive l 4.5 4.7 V EXTVCC CC INTVCC EXTVCC Oscillator f Oscillator Frequency C = 100pF (Note 4) 112 125 138 kHz OSC OSC 2 U W U W U WW