LTC1735 High Efficiency Synchronous Step-Down Switching Regulator FEATURES DESCRIPTIO n Synchronizable/Programmable Fixed Frequency The LTC 1735 is a synchronous step-down switching TM n OPTI-LOOP Compensation Minimizes C regulator controller that drives external N-channel power OUT n 1% Output Voltage Accuracy MOSFETs using a fixed frequency architecture. Burst TM n Dual N-Channel MOSFET Synchronous Drive Mode operation provides high efficiency at low load n Wide V Range: 4V to 36V Operation currents. The precision 0.8V reference is compatible with IN n V Range: 0.8V to 6V future generation microprocessors. OPTI-LOOP compen- OUT n Internal Current Foldback sation allows the transient response to be optimized over n Output Overvoltage Crowbar Protection a wide range of output capacitance and ESR values. n Latched Short-Circuit Shutdown Timer The operating frequency (synchronizable up to 500kHz) is with Defeat Option set by an external capacitor allowing maximum flexibility n Very Low Dropout Operation: 99% Duty Cycle in optimizing efficiency. A forced continuous control pin n Forced Continuous Control Pin reduces noise and RF interference and can assist second- n Optional Programmable Soft-Start ary winding regulation by disabling Burst Mode operation n Remote Output Voltage Sense when the main output is lightly loaded. n Power Good Output (LTC1735F Only) Protection features include internal foldback current lim- n Logic Controlled Micropower Shutdown: I < 25m A Q iting, output overvoltage crowbar and optional short- n LTC1435 Pin Compatible with circuit shutdown. Soft-start is provided by an external Minor Component Changes capacitor that can be used to properly sequence supplies. n Available in 16-Lead Narrow SSOP, SO Packages and The operating current level is user-programmable via an 20-Lead TSSOP Package (LTC1735F Only) 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. n Notebook and Palmtop Computers, PDAs Burst Mode and OPTI-LOOP are trademarks of Linear Technology Corporation. n Cellular Telephones and Wireless Modems n DC Power Distribution Systems TYPICAL APPLICATIO V IN C 5V TO 24V OSC C IN C SS M1 22F C 0.1F OSC TG FDS6680A C 50V 47pF B RUN/SS 0.22F C : PANASONIC EEFUEOG181R OUT C : MARCON THCR70E1H226ZT IN BOOST L1: PANASONIC ETQP6F2R0HFA I TH C C R : IRC LRF2010-01-R005J SENSE SW 330pF R C C C2 LTC1735 L1 R SENSE 100pF 33k D 2H B 0.005 V OUT SGND V IN CMDSH-3 1.6V R2 100pF 9A 20k V INTV OSENSE CC 1% C OUT + + 180F 4.7F D1 R1 M2 4V SENSE BG MBRS340T3 20k FDS6680A 4 1% 1000pF SP + SENSE PGND 1735 F01 Figure 1. High Efficiency Step-Down Converter 1735fc 1 U ULTC1735 ABSOLUTE AXI U RATI GS (Note 1) Input Supply Voltage (V ).........................36V to 0.3V Peak Driver Output Current <10m s (TG, BG) .............. 3A IN Topside Driver Supply Voltage (BOOST)....42V to 0.3V INTV Output Current ......................................... 50mA CC Switch Voltage (SW) ....................................36V to 5V Operating Ambient Temperature Range EXTV Voltage ...........................................7V to 0.3V LTC1735C ............................................... 0 C to 85 C CC Boosted Driver Voltage (BOOST SW) .......7V to 0.3V LTC1735I/LTC1735E (Note 8) ............ 40 C to 85 C + SENSE , SENSE Voltages .......... 1.1 (INTV ) to 0.3V Junction Temperature (Note 2)............................. 125 C CC FCB Voltage ............................(INTV + 0.3V) to 0.3V Storage Temperature Range ................. 65 C to 150 C CC I , V Voltages ...............................2.7V to 0.3V Lead Temperature (Soldering, 10 sec).................. 300 C TH OSENSE RUN/SS, PGOOD (LTC1735F Only) Voltages.......................................................7V to 0.3V UUW PACKAGE/ORDER I FOR ATIO ORDER PART ORDER PART TOP VIEW TOP VIEW NUMBER NUMBER NC 1 20 NC C 1 16 TG OSC C 2 19 TG OSC RUN/SS 2 15 BOOST LTC1735CGN LTC1735CF RUN/SS 3 18 BOOST I 3 14 SW TH LTC1735CS LTC1735IF I 4 17 SW TH FCB 4 13 V IN LTC1735IGN FCB 5 16 V IN SGND 5 12 INTV CC LTC1735IS SGND 6 15 INTV CC V 6 11 BG OSENSE LTC1735EGN V 7 14 BG OSENSE SENSE 7 10 PGND PGOOD 8 13 PGND + SENSE 8 9 EXTV CC GN PART MARKING SENSE 9 12 EXTV CC + GN PACKAGE S PACKAGE SENSE 10 11 NC 1735 16-LEAD NARROW 16-LEAD PLASTIC SO PLASTIC SSOP 1735I F PACKAGE 20-LEAD PLASTIC TSSOP T = 125 C, q = 130 C/W (GN) JMAX JA 1735E T = 125 C, q = 110 C/W (S) JMAX JA T = 125 C, q = 110 C/W JMAX JA Consult LTC marketing for parts specified with wider operating temperature ranges. ELECTRICAL CHARACTERISTICS The l denotes specifications which apply over the full operating temperature range, otherwise specifications are at T = 25 C. V = 15V, V = 5V unless otherwise noted. A IN RUN/SS SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS Main Control Loop I Feedback Current (Note 3) 4 25 nA VOSENSE V Feedback Voltage (Note 3) l 0.792 0.8 0.808 V OSENSE D V Reference Voltage Line Regulation V = 3.6V to 30V (Note 3) 0.001 0.02 %/V LINEREG IN D V Output Voltage Load Regulation (Note 3) LOADREG Measured in Servo Loop V = 0.7V l 0.1 0.3 % ITH Measured in Servo Loop V = 2V l 0.1 0.3 % ITH DF Max Maximum Duty Factor In Dropout 98 99.4 % g Transconductance Amplifier g 1.3 mmho m m V Forced Continuous Threshold l 0.76 0.8 0.84 V FCB I Forced Continuous Current V = 0.85V 0.17 0.3 m A FCB FCB 1735fc 2 U WWW