LTC3706 Secondary-Side Synchronous Forward Controller with PolyPhase Capability FEATURES DESCRIPTION n The LTC 3706 is a PolyPhase capable secondary-side Secondary-Side Control for Fast Transient Response n controller for synchronous forward converters. When used Self-Starting Architecture Eliminates Need for in conjunction with the LTC3705 gate driver and primary- Separate Bias Regulator n side controller, the part creates a complete isolated power Proprietary Gate Drive Encoding Scheme Reduces supply that combines the power of PolyPhase operation System Complexity n with the speed of secondary-side control. PolyPhase Operation Reduces C Requirements IN n Current Mode Control Ensures Current Sharing The LTC3706 has been designed to simplify the design n PLL Fixed Frequency: 100kHz to 500kHz of highly efficient, secondary-side forward converters. n 1% Output Voltage Accuracy Working in concert with the LTC3705, the LTC3706 forms n True Remote Sense Differential Amplifier a robust, self-starting converter that eliminates the need n Power Good Output Voltage Monitor for the separate bias regulator that is commonly used in n High Voltage Linear Regulator Controller secondary-side control applications. In addition, a pro- n Wide Supply Range: 5V to 30V prietary scheme is used to multiplex gate drive signals n Available in a Narrow 24-Lead SSOP Package and DC bias power across the isolation barrier through a single, tiny pulse transformer. APPLICATIONS The LTC3706 provides remote sensing, accurate power n Isolated 48V Telecommunication Systems good and overvoltage monitoring circuits to support preci- n Internet Servers and Routers sion, high current applications. A linear regulator controller n Distributed Power Step-Down Converters with thermal protection is also provided to simplify the n Automotive and Heavy Equipment generation of secondary-side bias voltage. L, LT, LTC, LTM, PolyPhase, Burst Mode, Linear Technology and the Linear logo are registered trademarks and No R and ThinSOT are trademarks of Linear Technology Corporation. SENSE The LTC3706 is available in a 24-lead SSOP package. All other trademarks are the property of their respective owners. Protected by U.S. Patents including 6144194, other patents pending. TYPICAL APPLICATION 36V-72V to 3.3V/20A Isolated Forward Converter + + V V IN OUT T1 L1 1.2H Si7852DP 1.2 MURS120 Si7336ADP 1F Si7852DP 330F 2 100V Si7336ADP 6.3V 3 CMPSH1-4 3 MURS120 2m 30m 10F 2W 1W 25V V V OUT IN CZT3019 100k 2.2F FQT7N10 102k L1: COILCRAFT SER2010-122 0.22F 16V 1% BAS21 T1: PULSE PA0807 T2: PULSE PA0297 FG SW SG V NDRV V IN CC I S 365k FS/SYNC 1F + NDRV TG TS BG IS I 1% BOOST S T2 + + FB UVLO FB/IN PT LTC3706 ITH 680pF V LTC3705 CC 2.2F FS/IN PT SS/FLT 25V 22.6k RUN/SS GND PGND PHASE SLP MODE REGSD GND PGND VSLMT 20k 15k 162k 1% 33nF 33nF 1% 3706 TA01 3706fd 1LTC3706 ABSOLUTE MAXIMUM RATINGS PIN CONFIGURATION (Note 1) TOP VIEW V ........................................................... 0.3V to 10V CC SG 1 24 V CC V ........................................................... 0.3V to 33V IN FG 2 23 PGND SW ............................................................... 5V to 50V + PGOOD 3 22 PT NDRV ......................................................... 0.3V to 13V MODE 4 21 PT + ITH, RUN/SS, V , V , V , REGSD ....... 0.3V to 7V SOUT S S PHASE 5 20 SW All Other Pins ............................................ 0.3V to 10V FB 6 19 V IN Operating Temperature Range (Note 2) ITH 7 18 NDRV LTC3706EGN .......................................40C to 85C RUN/SS 8 17 REGSD + LTC3706IGN ........................................40C to 85C V 9 16 I S SOUT + Junction Temperature (Note 3) ............................ 125C V 10 15 I S S V 11 14 SLP Storage Temperature Range .................. 65C to 150C S GND 12 13 FS/SYNC Lead Temperature (Soldering, 10 sec) ...................300C GN PACKAGE 24-LEAD PLASTIC SSOP T = 125C, = 130C/W JMAX JA ORDER INFORMATION LEAD FREE FINISH TAPE AND REEL PART MARKING PACKAGE DESCRIPTION TEMPERATURE RANGE LTC3706EGN PBF LTC3706EGN TRPBF LTC3706EGN 24-Lead Plastic SSOP 40C to 85C LTC3706IGN PBF LTC3706IGN TRPBF LTC3706IGN 24-Lead Plastic SSOP 40C to 85C LEAD BASED FINISH TAPE AND REEL PART MARKING PACKAGE DESCRIPTION TEMPERATURE RANGE LTC3706EGN LTC3706EGN TR LTC3706EGN 24-Lead Plastic SSOP 40C to 85C LTC3706IGN LTC3706IGN TR LTC3706IGN 24-Lead Plastic SSOP 40C to 85C Consult LTC Marketing for parts specified with wider operating temperature ranges. For more information on lead free part marking, go to: