POWER LOSS (W) LT3845A High Voltage Synchronous Current Mode Step-Down Controller with Adjustable Operating Frequency FEATURES DESCRIPTION n High Voltage Operation: Up to 60V The LT 3845A is a high voltage, synchronous, current n Synchronizable Up to 600kHz mode controller used for medium to high power, high n Adjustable Constant Frequency: 100kHz to 500kHz efficiency supplies. It offers a wide 4V to 60V input range n Output Voltages Up to 36V (7.5V minimum start-up voltage). An onboard regulator n Stable Operation in Current Limit simplifies the biasing requirements by providing IC power n Adaptive Nonoverlap Circuitry Prevents Switch directly from V . IN Shoot-Through Burst Mode operation maintains high efficiency at light n Reverse Inductor Current Inhibit for Discontinuous loads by reducing IC quiescent current to 120A. Light load Operation Improves Efficiency with Light Loads efficiency is also improved with the reverse inductor current n Programmable Soft-Start inhibit function which supports discontinuous operation. n 120A No Load Quiescent Current n Additional features include adjustable fixed operating 10A Shutdown Supply Current n frequency that can be synchronized to an external clock 1% Regulation Accuracy n for noise sensitive applications, gate drivers capable of Standard Gate N-Channel Power MOSFETs n driving large N-channel MOSFETs, a precision undervoltage Reverse Overcurrent Protection n lockout, 10A shutdown current, short-circuit protection 16-Lead Thermally Enhanced TSSOP Package and a programmable soft-start. APPLICATIONS The LT3845A is available in a 16-lead thermally enhanced n 12V and 42V Automotive and Heavy Equipment TSSOP package. n 48V Telecom Power Supplies L, LT, LTC, LTM, Burst Mode, Linear Technology and the Linear logo are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners.. n Avionics and Industrial Control Systems Protected by U.S. Patents, including 5481178, 6611131, 6304066, 6498466, 6580258. n Distributed Power Converters TYPICAL APPLICATION High Voltage Step-Down Regulator 48V to 12V at 75W Efficiency and Power Loss V vs Load Current IN 20V 0.1F TO 55V 2.2F 100 7 V = 48V 1M IN 100V V BOOST IN 47F 95 6 63V SHDN TG Si7370DP 1500pF LT3845A BAS521 15H 90 5 0.008 V OUT C SS SW 82.5k 12V 75W 4 85 V BURST EN CC B160 33F Si7370DP V 3 80 3 FB BG 20k 16.2k V C PGND 75 2 100pF LOSS + SYNC SENSE 70 1 f 1F SET SENSE 2200pF SGND 65 0 143k 49.9k 1N4148 0.1 1 10 LOAD CURENT (A) 3845A TA01b 3845A TA01a 3845afa 1 EFFICIENCY(%)LT3845A ABSOLUTE MAXIMUM RATINGS PIN CONFIGURATION (Note 1) TOP VIEW Input Supply Voltage (V ) ........................................65V IN V 1 16 BOOST IN Boosted Supply Voltage (BOOST) .............................80V SHDN 2 15 TG Switch Voltage (SW) (Note 8) ....................... 65V to 2V C 3 14 SW SS Differential Boost Voltage BURST EN 4 13 V CC (BOOST to SW) .....................................................24V 17 V 5 12 BG FB Bias Supply Voltage (V ) .........................................24V CC V 6 11 PGND C + SENSE and SENSE Voltages ..................................40V + SYNC 7 10 SENSE Differential Sense Voltage f 8 9 SENSE SET + (SENSE to SENSE ) ....................................1V to 1V FE PACKAGE BURST EN Voltage ...................................................24V 16-LEAD PLASTIC TSSOP SYNC, V , V , C , and SHDN Voltages ....................5V T = 125C, q = 40C/W, q = 10C/W JMAX JA JC C FB SS EXPOSED PAD (PIN 17) IS SGND, MUST BE SOLDERED TO PCB SHDN Pin Currents ..................................................1mA Operating Junction Temperature Range (Note 2) LT3845AE (Note 3) ............................ 40C to 125C LT3845AI .......................................... 40C to 125C LT3845AMP ....................................... 55C to 125C Storage Temperature.............................. 65C to 150C Lead Temperature (Soldering, 10 sec) ...................300C ORDER INFORMATION LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE LT3845AEFE PBF LT3845AEFE TRPBF 3845AFE 16-Lead Plastic TSSOP 40C to 125C LT3845AIFE PBF LT3845AIFE TRPBF 3845AFE 16-Lead Plastic TSSOP 40C to 125C LT3845AMPFE PBF LT3845AMPFE TRPBF 3845AFE 16-Lead Plastic TSSOP 55C to 125C Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container. Consult LTC Marketing for information on non-standard lead based finish parts. For more information on lead free part marking, go to: