LTC3900 Synchronous Rectifier Driver for Forward Converters Fea T Descrip T n N-Channel Synchronous Rectifier MOSFET Driver The LTC 3900 is a secondary-side synchronous recti- n Programmable Timeout Protection fier driver designed to be used in isolated forward con- n Reverse Inductor Current Protection verter power supplies. The chip drives N-channel rectifier n Pulse Transformer Synchronization MOSFETs and accepts pulse sychronization from the n Wide V Supply Range: 4.5V to 11V primary-side controller via a pulse transformer. CC n 15ns Rise/Fall Times at V = 5V, C = 4700pF CC L The LTC3900 incorporates a full range of protection for the n Undervoltage Lockout external MOSFETs. A programmable timeout function is n Small SO-8 Package included that disables both drivers when the synchroniza- tion signal is missing or incorrect. Additionally, the chip senses the output inductor current through the drain-source a T resistance of the catch MOSFET, shutting off the MOSFET n 48V Input Isolated DC/DC Converters if the inductor current reverses. The LTC3900 also shuts n Isolated Telecom Power Supplies off the drivers if the supply voltage is too low. n High Voltage Distributed Power L, LT, LTC, LTM, Linear Technology, Burst Mode and the Linear logo are registered trademarks Step-Down Converters of Linear Technology Corporation. All other trademarks are the property of their respective n Industrial Control System Power Supplies owners. n Automotive and Heavy Equipment Typical a T ISOLATION BARRIER L0 V OUT V IN 3.3V 36V TO 72V + D3 40A C OUT Efficiency T1 C R Z Z 95 GATE V = 3.3V OUT Q REG R Q1 CS2 R B 90 R D CS1 V = 36V Z IN OUT Q3 + CS V = 72V IN OC 85 CG Q4 470 V = 48V IN V I CC SENSE CS 80 R TMR R LTC3900 CS3 10m LT1952 C TIMER VCC FG 75 C SG C TMR S SYNC OUT GND 70 GND COMP SG T2 R SYNC 270 65 0 5 10 15 20 25 30 35 40 LOAD CURRENT (A) R1 OPTO V IN 3900 F10b LT4430 COMP GND OCI OC FB R2 3900 F01 Figure 1. Simplified Isolated Synchronous Forward Converter 3900fb 1 EFFICIENCY (%) ion pplica ions pplica ion uresLTC3900 a Te Maxi Mu M r a T p in c F T (Note 1) Supply Voltage TOP VIEW V ........................................................................12V CC + CS 1 8 SYNC Input Voltage CS 2 7 TIMER CS , TIMER .............................. 0.3V to (V +0.3V) CC CG 3 6 GND SYNC ...................................................... 12V to 12V V 4 5 FG CC Input Current + S8 PACKAGE CS ....................................................................15mA 8-LEAD PLASTIC SO T = 150C, = 130C/W JMAX JA Operating Junction Temperature Range (Note 2) LTC3900E ........................................... 40C to 125C LTC3900I............................................ 40C to 125C LTC3900H .......................................... 40C to 150C LTC3900MP ....................................... 55C to 150C Storage Temperature Range ................... 65C to 150C Lead Temperature (Soldering, 10 sec) .................. 300C Der in F Ma T LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE LTC3900ES8 PBF LTC3900ES8 TRPBF 3900 8-Lead Plastic Small Outline 40C to 125C LTC3900IS8 PBF LTC3900IS8 TRPBF 3900 8-Lead Plastic Small Outline 40C to 125C LTC3900HS8 PBF LTC3900HS8 TRPBF 3900 8-Lead Plastic Small Outline 40C to 150C LTC3900MPS8 PBF LTC3900MPS8 TRPBF 3900 8-Lead Plastic Small Outline 55C to 150C LEAD BASED FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE LTC3900ES8 LTC3900ES8 TR 3900 8-Lead Plastic Small Outline 40C to 125C LTC3900IS8 LTC3900IS8 TR 3900 8-Lead Plastic Small Outline 40C to 125C LTC3900HS8 LTC3900HS8 TR 3900 8-Lead Plastic Small Outline 40C to 150C LTC3900MPS8 LTC3900MPS8 TR 3900 8-Lead Plastic Small Outline 55C to 150C Consult LTC Marketing for parts speciefi d with wider operating temperature ranges. *The temperature grade is identiefi d by a label on the shipping container. For more information on lead free part marking, go to: