POWER LOSS (W) LT3845 High Voltage Synchronous Current Mode Step-Down Controller with Adjustable Operating Frequency FEATURES DESCRIPTION High Voltage Operation: Up to 60V The LT 3845 is a high voltage, synchronous, current Synchronizable Up to 600kHz mode controller used for medium to high power, high Adjustable Constant Frequency: 100kHz to 500kHz ef ciency supplies. It offers a wide 4V to 60V input range Output Voltages Up to 36V (7.5V minimum start-up voltage). An onboard regulator Adaptive Nonoverlap Circuitry Prevents Switch simpli es the biasing requirements by providing IC power Shoot-Through directly from V . IN Reverse Inductor Current Inhibit for Discontinuous Burst Mode operation maintains high ef ciency at light Operation Improves Ef ciency with Light Loads loads by reducing IC quiescent current to 120A. Light Programmable Soft-Start load ef ciency is also improved with the reverse inductor 120A No Load Quiescent Current current inhibit function which supports discontinuous 10A Shutdown Supply Current operation. 1% Regulation Accuracy Additional features include adjustable xed operating Standard Gate N-Channel Power MOSFETs frequency that can be synchronized to an external clock Current Limit Unaffected by Duty Cycle for noise sensitive applications, gate drivers capable of Reverse Overcurrent Protection driving large N-channel MOSFETs, a precision undervoltage 16-Lead Thermally Enhanced TSSOP Package, lockout, 10A shutdown current, short-circuit protection 16-Pin PDIP and a programmable soft-start. APPLICATIONS The LT3845 is available in a 16-lead thermally enhanced 12V and 42V Automotive and Heavy Equipment TSSOP package and 16-pin through hole N package. 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 Avionics and Industrial Control Systems owners.. Protected by U.S. Patents, including 5481178, 6611131, 6304066, 6498466, 6580258. Distributed Power Converters TYPICAL APPLICATION Ef ciency and Power Loss vs High Voltage Step-Down Regulator 48V to 12V at 75W Load Current V IN 100 7 20V TO 55V V = 48V IN 0.1F 2.2F 100V 1M 95 6 V BOOST IN 47F Si7370DP 63V SHDN TG 5 90 0.01 V LT3845 OUT 1500pF C SW 12V 82.5k SS 85 4 BAS521 15H 75W BURST EN V CC B160 33F 3 80 Si7370DP 3 V BG FB 20k 75 2 V PGND C LOSS 100pF 16.2k + SYNC SENSE 70 1 2200pF 1F f SENSE SET 65 0 SGND 49.9k 1N4148 0.1 1 10 143k LOAD CURENT (A) 3845 TA01a 3845 TA01b 3845fd 1 EFFICIENCY(%)LT3845 (Note 1) ABSOLUTE MAXIMUM RATINGS Input Supply Voltage (V ) ........................................65V BURST EN Voltage ...................................................24V IN Boosted Supply Voltage (BOOST) .............................80V SYNC, V , V , C , and SHDN Voltages ....................5V C FB SS Switch Voltage (SW) (Note 8) ....................... 65V to 2V SHDN Pin Currents ..................................................1mA Differential Boost Voltage Operating Junction Temperature Range (Note 2) (BOOST to SW) .....................................................24V LT3845E (Note 3) ............................... 40C to 125C Bias Supply Voltage (V ) ......................................... 24V LT3845I .............................................. 40C to 125C CC + SENSE and SENSE Voltages ..................................40V LT3845MP.......................................... 55C to 125C Differential Sense Voltage Storage Temperature .............................. 65C to 150C + (SENSE to SENSE ) ................................... 1V to 1V Lead Temperature (Soldering, 10 sec) .................. 300C PIN CONFIGURATION TOP VIEW TOP VIEW V 1 16 BOOST V 1 16 BURST EN IN FB SHDN 2 15 TG V 2 15 C C SS C 3 14 SW f 3 14 SHDN SS SET BURST EN 4 13 V SGND 4 13 V CC IN 17 V 5 12 BG SENSE 5 12 BOOST FB + V 6 11 PGND SENSE 6 11 TG C + SYNC 7 10 SENSE PGND 7 10 SW f 8 9 SENSE BG 8 9 V SET CC FE PACKAGE N PACKAGE 16-LEAD PLASTIC TSSOP 16-LEAD PDIP T = 125C, = 40C/W, = 10C/W T = 125C, = 70C/W, = 34C/W JMAX JA JC JMAX JA JC EXPOSED PAD (PIN 17) IS SGND, MUST BE SOLDERED TO PCB ORDER INFORMATION LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE LT3845EFE PBF LT3845EFE TRPBF 3845FE 16-Lead Plastic TSSOP 40C to 125C LT3845IFE PBF LT3845IFE TRPBF 3845FE 16-Lead Plastic TSSOP 40C to 125C LT3845MPFE PBF LT3845MPFE TRPBF 3845FE 16-Lead Plastic TSSOP 55C to 125C LT3845EN PBF LT3845EN TRPBF 3845N 16-Lead PDIP 40C to 125C Consult LTC Marketing for parts speci ed with wider operating temperature ranges. *The temperature grade is identi ed by a label on the shipping container. Consult LTC Marketing for information on non-standard lead based nish parts. For more information on lead free part marking, go to: