LT3431 High Voltage, 3A, 500kHz Step-Down Switching Regulator FEATURES DESCRIPTIO n Wide Input Range: 5.5V to 60V The LT 3431 is a 500kHz monolithic buck switching regu- n 3A Peak Switch Current lator that accepts input voltages up to 60V. A high efficiency n Small Thermally Enhanced 16-Pin TSSOP Package 3A, 0.1W switch is included on the die along with all the nec- n Constant 500kHz Switching Frequency essary oscillator, control and logic circuitry. A current mode n Saturating Switch Design: 0.1W architecture provides fast transient response and good loop n Peak Switch Current Maintained Over stability. Full Duty Cycle Range Special design techniques and a new high voltage process n Effective Supply Current: 2.5mA achieve high efficiency over a wide input range. Efficiency n Shutdown Current: 30m A is maintained over a wide output current range by using the n 1.2V Feedback Reference Voltage output to bias the circuitry and by utilizing a supply boost n Easily Synchronizable capacitor to saturate the power switch. Patented circuitry n Cycle-by-Cycle Current Limiting maintains peak switch current over the full duty cycle range. U A shutdown pin reduces supply current to 30m A and the de- APPLICATIO S vice can be externally synchronized from 580kHz to 700kHz with logic level inputs. n Industrial and Automotive Power Supplies n The LT3431 is available in a thermally enhanced 16-pin Portable Computers n TSSOP package. Battery Chargers n Distributed Power Systems , LTC and LT are registered trademarks of Linear Technology Corporation. TYPICAL APPLICATIO 5V, 2A Buck Converter MMSD914TI 6 0.22F Efficiency vs Load Current BOOST 10H** V V IN OUT 3, 4 2, 5 12V V SW 5V IN 100 (TRANSIENTS 2A 2.2F V = 12V IN TO 60V) 30BQ060 LT3431 100V L = 15H V = 5V OUT CERAMIC 47F 90 15 10 CERAMIC SHDN BIAS V = 3.3V OUT 15.4k 14 12 80 SYNC FB GND V C 4.99k 70 1, 8, 9, 16 11 220pF 60 1.5k 15nF 50 0 0.5 1.0 1.5 2.0 2.5 LOAD CURRENT (A) **INCREASE INDUCTOR VALUE FOR LOAD CURRENTS ABOVE 2A 3431 TA02 (SEE APPLICATIONS INFORMATIONMAXIMUM OUTPUT LOAD CURRENT) 3431 TA01 UNITED CHEMI-CON THCS50EZA225ZT sn3431 3431fs 1 EFFICIENCY (%) U ULT3431 UUW ABSOLUTE AXI U RATI GS PACKAGE/ORDER I FOR ATIO (Note 1) Input Voltage (V ) ................................................. 60V IN ORDER PART TOP VIEW BOOST Pin Above SW ............................................ 35V NUMBER GND 1 16 GND BOOST Pin Voltage ................................................. 68V SW 2 15 SHDN LT3431EFE V 3 14 SYNC IN SYNC Voltage ........................................................... 7V V 4 13 NC IN LT3431IFE SHDN Voltage ........................................................... 6V SW 5 12 FB BIAS Pin Voltage .................................................... 30V BOOST 6 11 V C NC 7 10 BIAS FB Pin Voltage/Current .................................. 3.5V/2mA GND 8 9 GND FE PART MARKING Operating Junction Temperature Range FE PACKAGE LT3431EFE (Notes 8, 10) ................. 40 C to 125 C 16-LEAD PLASTIC TSSOP 3431EFE T = 125 C, q = 45 C/ W, q (PAD) = 10 C/W JMAX JA JC LT3431IFE (Notes 8, 10) ................. 40 C to 125 C 3431IFE EXPOSED PAD MUST BE SOLDERED Storage Temperature Range ................ 65 C to 150 C TO GROUND PLANE Lead Temperature (Soldering, 10 sec)................. 300 C 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. J V = 15V, V = 1.5V, SHDN = 1V, BOOST open circuit, SW open circuit, unless otherwise noted. IN C PARAMETER CONDITIONS MIN TYP MAX UNITS Reference Voltage (V ) 5.5V V 60V 1.204 1.219 1.234 V REF IN V + 0.2 V V 0.2 l 1.195 1.243 V OL C OH FB Input Bias Current l 0.2 1.5 m A Error Amp Voltage Gain (Note 2) 200 475 V/V Error Amp g dl (V ) = 10m A 1650 2200 3300 m Mho m C l 1000 4200 m Mho V to Switch g 3.4 A/V C m EA Source Current FB = 1V or V = 4.1V l 125 275 450 m A SENSE EA Sink Current FB = 1.4V or V = 5.7V l 100 275 500 m A SENSE V Switching Threshold Duty Cycle = 0 0.8 V C V High Clamp SHDN = 1V 2.1 V C Switch Current Limit V Open, BOOST = V + 5V, FB = 1V or V = 4.1V 40 C Tj 25 C 3.0 5 6.5 A C IN SENSE (Note 9) Tj = 125 C 2.5 4 5.5 A Switch On Resistance I = 2.5A, BOOST = V + 5V (Note 7) 0.1 0.14 W SW IN l 0.18 W Maximum Switch Duty Cycle FB = 1V or V = 4.1V 88 92 % SENSE l 80 % Switch Frequency V Set to Give DC = 50% 460 500 540 kHz C l 430 500 570 kHz f Line Regulation 5.5V V 60V l 0.05 0.15 %/V SW IN f Shifting Threshold Df = 10kHz 0.8 V SW sn3431 3431fs 2 U WWW