LT8311EFE#PBF Analog Devices

LT8311 Synchronous Rectifier Controller with Opto-Coupler Driver for Forward Converters FEATURES DESCRIPTION n Wide Input Supply Range: 3.7V to 30V The LT 8311 is used on the secondary side of a forward n Preactive Mode: converter to provide synchronous MOSFET control and n No Pulse Transformer Required output voltage feedback through an opto-coupler. The n DCM Operation at Light Load LT8311s unique preactive mode allows control of the n SYNC Mode: secondary-side MOSFETs without requiring a traditional n FCM or DCM Operation at Light Load pulse transformer for primary- to secondary-side com- n Achieves Highest Efficiency munication. In preactive mode, the output inductor current n 1.5% Feedback Voltage Reference operates in discontinuous conduction mode (DCM) at n 10mA Opto-Coupler Driver light load. If forced continuous mode (FCM) operation is n Output Power Good Indicator desired at light load, the LT8311 can, alternatively, be used n Integrated Soft-Start Function in SYNC mode, where a pulse transformer is required to send synchronous control signals from the primary-side APPLICATIONS IC to the LT8311. n Offline and HV Car Battery Isolated Power Supplies The LT8311 offers a full featured opto-coupler controller, n 48V Isolated Power Supplies incorporating a 1.5% reference, a transconductance error n Industrial, Automotive and Military Systems amplifier and a 10mA opto-driver. Power good monitoring and output soft-start/overshoot control are also included. L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. The LT8311 is available in a 16-lead FE package with pins removed for high voltage spacing requirements. TYPICAL APPLICATION 18V to 72V, 12V/8A Active Clamp Isolated Forward Converter 4:4 6.8H V V IN OUT 18V to 12V 4.7F + 68pF 72V 20k 3 100k 470F V IN 22F 2.2F UVLO VSEC 2 100nF 2.2nF 100V 2k 5.9k 100nF FSW 100k OVLO AOUT FG FB 2k 1.82k 11.3k CSW LT3753 10k LT8311 1.78k CSP IVSEC OUT CG V V IN OUT 240kHz RT 2k 71.5k 1.78k 100k ISENSEP SYNC 31.6k CSN PGOOD OC S OUT 6m 1.5k OPTO INTV CC TAO ISENSEN COMP 4.7F TAS SYNC PMODE 15nF 49.9k TOS INTV 2.2F CC SS TIMER GND TBLNK COMP 100 4.7F GND SS1 SS2 FB 100k 124k 2.94k 10pF 1F 1F 0.47F 34k 100k 1F 8311 TA01 1k 2.2nF 8311f 1 For more information www.linear.com/LT8311LT8311 TABLE OF CONTENTS Features ............................................................................................................................ 1 Applications ....................................................................................................................... 1 Typical Application ............................................................................................................... 1 Description......................................................................................................................... 1 Absolute Maximum Ratings ..................................................................................................... 3 Order Information ................................................................................................................. 3 Pin Configuration ................................................................................................................. 3 Electrical Characteristics ........................................................................................................ 4 Typical Performance Characteristics .......................................................................................... 7 Pin Functions .....................................................................................................................11 Block Diagram ....................................................................................................................12 Operation..........................................................................................................................13 FUNDAMENTALS OF FORWARD CONVERTER OPERATION IN CCM ..................................................................... 13 LT8311 SYNCHRONOUS CONTROL SCHEMES ..................................................................................................... 17 PREACTIVE MODE SYNCHRONOUS CONTROL .................................................................................................... 17 SYNC MODE SYNCHRONOUS CONTROL ............................................................................................................. 19 OPTO-COUPLER CONTROL .................................................................................................................................. 21 Applications Information .......................................................................................................25 V BIAS SUPPLY .................................................................................................................................................. 25 IN INTV BIAS SUPPLY ............................................................................................................................................ 26 CC LT8311 OPTO CONTROL FUNDAMENTALS ........................................................................................................... 27 LT8311 SYNCHRONOUS CONTROL FUNDAMENTALS .......................................................................................... 31 PREACTIVE MODE SYNCHRONOUS CONTROL ................................................................................................... 37 SYNC MODE SYNCHRONOUS CONTROL ............................................................................................................ 38 Typical Applications .............................................................................................................40 Package Description ............................................................................................................47 Typical Application ..............................................................................................................48 Related Parts .....................................................................................................................48 8311f 2 For more information www.linear.com/LT8311