LT3752/LT3752-1 Active Clamp Synchronous Forward Controllers with Internal Housekeeping Controller FEATURES DESCRIPTION n Input Voltage Range: LT3752: 6.5V to 100V, The LT 3752/LT3752-1 are current mode PWM controllers LT3752-1:Limited Only by External Components optimized for an active clamp forward converter topology. n Internal Housekeeping DC/DC Controller A DC/DC housekeeping controller is included for improved n Programmable Volt-Second Clamp efficiency and performance. The LT3752 allows operation n High Efficiency Control: Active Clamp, up to 100V input and the LT3752-1 is optimized for ap- Synchronous Rectification, Programmable Delays plications with input voltages greater than 100V. n Short-Circuit (Hiccup Mode) Overcurrent Protection A programmable volt-second clamp allows primary switch n Programmable Soft-Start/Stop duty cycles above 50% for high switch, transformer and n Programmable OVLO and UVLO with Hysteresis rectifier utilization. Active clamp control reduces switch n Programmable Frequency (100kHz to 500kHz) voltage stress and increases efficiency. A synchronous n Synchronizable to an External Clock output is available for controlling secondary side syn- n AEC-Q100 Qualified for Automotive Applications chronous rectification. APPLICATIONS The LT3752/LT3752-1 are available in a 38-lead plastic TSSOP package with missing pins for high voltage n Offline and HV Car Battery Isolated Power Supplies spacings. n 48V Telecommunication Isolated Power Supplies All registered trademarks and trademarks are the property of their respective owners. Protected n Industrial, Automotive and Military Systems by U.S. patents, including XXXXX, XXXXX. TYPICAL APPLICATION 18V to 72V, 12V/12.5A, 150W Active Clamp Isolated Forward Converter V OUT V IN 12V 18V TO 72V 6.8H 12.5A 4:4 INTV V 4.7F CC AUX + 470F 100V 16V 3 2.2F 2.2F 15nF ZVN4525E6 22F BSC077N12NS3 Si2325DS FDMS86101 16V 100nF 2 499 0.15 10k 100 100 BSC077N12NS3 HOUT HI AOUT V SENSE OUT IN V V AUX IN OC 2.2F 68pF SYNC I 100k SENSEP GND 100k 100k 2k UVLO V 0.006 SEC LT8311 FB PGOOD 5.9k SYNC 11.3k I SENSEN LT3752 220pF OVLO 560 1.82k SOUT INTV CC V INTV AUX CC GND 220nF 3.16k 13.7k 10k 100 68pF 4.7F 499k 4.7F HFB 4.7nF 1.1k 1F 3752 TA01 22.6k 22nF 34k 31.6k 2.8k 100k 49.9k 71.5k 0.33F 22nF 7.32k 100k 1.2k 2.2nF EFFICIENCY: 94% AT 48V /10A IN OUT Rev. C 1 Document Feedback For more information www.analog.com T AO T AS T OS T BLNK IVSEC RT SS1 SS2 HCOMP FB COMP OPTO FG F SW INTV CC C SW PMODE TIMER C G SS CSN COMP CSPLT3752/LT3752-1 TABLE OF CONTENTS Features ..................................................... 1 FORWARD CONTROLLER .......................................27 Applications ................................................ 1 Adaptive Leading Edge Blanking Plus Typical Application ........................................ 1 Programmable Extended Blanking......................27 Description.................................................. 1 Current Sensing and Programmable Slope Table of Contents .......................................... 2 Compensation ....................................................28 Absolute Maximum Ratings .............................. 3 Overcurrent: Hiccup Mode ..................................28 Order Information .......................................... 3 Programming Maximum Duty Cycle Clamp: D VSEC Pin Configuration .......................................... 3 (Volt-Second Clamp) ..........................................29 Electrical Characteristics ................................. 4 D Open Loop Control: No Opto-Coupler, Error VSEC Pin Functions .............................................. 13 Amplifier or Reference ........................................30 Block Diagram ............................................. 15 R : Open Pin Detection Provides Safety .......30 IVSEC Timing Diagrams ......................................... 16 Transformer Reset: Active Clamp Technique .....30 Operation................................................... 19 LO Side Active Clamp Topology (LT3752) ...........32 Introduction ....................................................... 19 HI Side Active Clamp Topology (LT3752-1) .........33 LT3752 Part Start-Up ......................................... 19 Active Clamp Capacitor Value and LT3752-1 Part Start-Up ...................................... 19 Voltage Ripple ....................................................33 Applications Information ................................ 21 Active Clamp MOSFET Selection ........................34 Programming System Input Undervoltage Lockout Programming Active Clamp Switch Timing: AOUT (UVLO) Threshold and Hysteresis ......................21 to OUT (t ) and OUT to AOUT (t ) Delays .......35 AO OA Soft-Stop Shutdown ...........................................21 Programming Synchronous Rectifier Timing: Micropower Shutdown .......................................21 SOUT to OUT (t ) and OUT to SOUT (t ) SO OS Programming System Input Overvoltage Lockout Delays .................................................................35 (OVLO) Threshold ...............................................21 Soft-Start (SS1, SS2) .........................................36 LT3752-1 Micropower Start-Up from High System Soft-Stop (SS1) ..................................................36 Input Voltages ....................................................22 Hard-Stop (SS1, SS2) .........................................37 Programming Switching Frequency ....................23 OUT, AOUT, SOUT Pulse-Skipping Mode ............37 Synchronizing to an External Clock ....................23 AOUT Timeout ....................................................38 INTV Regulator Bypassing and Operation ...... 24 Main Transformer Selection ...............................38 CC HOUSEKEEPING CONTROLLER .............................. 24 Primary-Side Power MOSFET Selection .............40 Housekeeping: Operation ....................................25 Synchronous Control (SOUT) .............................40 Housekeeping: Soft-Start/Shutdown ..................25 Output Inductor Value ......................................... 41 Housekeeping: Programming Output Voltage .....25 Output Capacitor Selection ................................. 41 Housekeeping: Programming Cycle-by-Cycle Peak Input Capacitor Selection ................................... 41 Inductor Current and Slope Compensation .........25 PCB Layout / Thermal Guidelines ......................42 Housekeeping: Adaptive Leading Edge Blanking .26 Typical Applications ...................................... 44 Housekeeping: Overcurrent Hiccup Mode ...........26 Package Description ..................................... 50 Housekeeping: Output Overvoltage and Power Revision History .......................................... 51 Good ..................................................................26 Typical Application ....................................... 52 Housekeeping: Transformer Turns Ratio and Related Parts .............................................. 52 Leakage Inductance ............................................26 Housekeeping: Operating Without This Supply ...27 Rev. C 2 For more information www.analog.com