LTC3726 Secondary-Side Synchronous Forward Controller DESCRIPTIO FEATURES Secondary-Side Control for Fast Transient Response The LTC 3726 is a secondary-side controller for synchro- Self-Starting Architecture Eliminates Need for nous forward converters. When used in conjunction with Separate Bias Regulator the LTC3705/LTC3725 gate driver and primary-side con- Proprietary Gate Drive Encoding Scheme Reduces trollers, the part creates a complete isolated power supply System Complexity that combines the simplicity of OPTI-LOOP compensa- Current Mode Control Ensures Current Sharing tion with the speed of secondary-side control. PLL Fixed Frequency: 100kHz to 500kHz The LTC3726 has been designed to simplify the design of 1% Output Voltage Accuracy highly efficient, secondary-side forward converters. Work- OPTI-LOOP Compensation ing in concert with the LTC3705 or LTC 3725, the LTC3726 Available in a Narrow 16-Lead SSOP Package forms a robust, self-starting converter that eliminates the U need for the separate bias regulator that is commonly used APPLICATIO S in secondary-side control applications. In addition, a pro- Isolated 48V Telecommunication Systems prietary scheme is used to multiplex gate drive signals and Internet Servers and Routers DC bias power across the isolation barrier through a Distributed Power Step-Down Converters single, tiny pulse transformer. Automotive and Heavy Equipment The LTC3726 is available in a 16-lead SSOP package. , LT, LTC and LTM are registered trademarks of Linear Technology Corporation. OPTI-LOOP is a registered trademark of Linear Technology Corporation. All other trademarks are the property of their respective owners. Protected by U.S. Patents, including 6144194. Other patents pending. TYPICAL APPLICATIO 36V-72V to 3.3V/20A Isolated Forward Converter + + V V IN OUT T1 L1 1.2H 1.2 Si7852DP MURS120 CMPSH1-4 5k 1F Si7852DP 330F 100V Si7336ADP Si7336ADP 6.3V x3 FZT690B 2 3 MURS120 2m 30m 10F 7.5V 2.2F 2W 1W 25V V V OUT IN 100k FQT7N10 102k L1: COILCRAFT SER2010-122 0.22F 1% T1: PULSE PA0807 BAS21 T2: PULSE PA0297 FG SW SG V CC I S 365k FS/SYNC 1F + I 1% NDRV BOOST TG TS BG IS S T2 + + UVLO FB/IN PT FB/PHASE LTC3726 ITH 680pF V LTC3705 CC 2.2F FS/IN PT SS/FLT 25V 22.6k GND PGND VSLMT RUN/SS GND PGND SLP MODE 15k 20k 162k 1% 33nF 1% 33nF 3726 TA01 3726fb 1 U ULTC3726 ABSOLUTE MAXIMUM RATINGS PACKAGE/ORDER INFORMATION (Note 1) TOP VIEW V ........................................................... 0.3V to 10V CC SW............................................................... 5V to 50V 1 SG 16 V CC + 2 ITH, RUN/SS ............................................... 0.3V to 7V FG 15 PT 3 MODE 14 PT All Other Pins............................................ 0.3V to 10V 4 FB/PHASE 13 PGND Operating Ambient Temperature Range (Note 2) 5 ITH 12 SW LTC3726EGN ...................................... 40C to 85C + 6 RUN/SS 11 IS LTC3726IGN ....................................... 40C to 85C 7 SLP 10 IS Operating Junction Temperature (Note 3) ........... 125C 8 GND 9 FS/SYNC Storage Temperature Range ................. 65C to 150C GN PACKAGE Lead Temperature (Soldering, 10 sec).................. 300C 16-LEAD PLASTIC SSOP T = 125C, = 130C/W JMAX JA ORDER PART NUMBER LTC3726EGN LTC3726IGN Order Options Tape and Reel: Add TR Lead Free: Add PBF Lead Free Tape and Reel: Add TRPBF Lead Free Part Marking: