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LT8311 Dataheets PDF



Part Number LT8311
Manufacturers Linear
Logo Linear
Description Synchronous Rectifier Controller
Datasheet LT8311 DatasheetLT8311 Datasheet (PDF)

FEATURES LT8311 Synchronous Rectifier Controller with Opto-Coupler Driver for Forward Converters DESCRIPTION n Wide Input Supply Range: 3.7V to 30V n Preactive Mode: n No Pulse Transformer Required n DCM Operation at Light Load n SYNC Mode: n FCM or DCM Operation at Light Load n Achieves Highest Efficiency n 1.5% Feedback Voltage Reference n 10mA Opto-Coupler Driver n Output Power Good Indicator n Integrated Soft-Start Function APPLICATIONS n Offline and HV Car Battery Isol.

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FEATURES LT8311 Synchronous Rectifier Controller with Opto-Coupler Driver for Forward Converters DESCRIPTION n Wide Input Supply Range: 3.7V to 30V n Preactive Mode: n No Pulse Transformer Required n DCM Operation at Light Load n SYNC Mode: n FCM or DCM Operation at Light Load n Achieves Highest Efficiency n 1.5% Feedback Voltage Reference n 10mA Opto-Coupler Driver n Output Power Good Indicator n Integrated Soft-Start Function APPLICATIONS n Offline and HV Car Battery Isolated Power Supplies n 48V Isolated Power Supplies n Industrial, Automotive and Military Systems 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 LT®8311 is used on the secondary side of a forward converter to provide synchronous MOSFET control and output voltage feedback through an opto-coupler. The LT8311’s unique preactive mode allows control of the secondary-side MOSFETs without requiring a traditional pulse transformer for primary- to secondary-side communication. In preactive mode, the output inductor current operates in discontinuous conduction mode (DCM) at light load. If forced continuous mode (FCM) operation is desired at light load, the LT8311 can, alternatively, be used in SYNC mode, where a pulse transformer is required to send synchronous control signals from the primary-side IC to the LT8311. The LT8311 offers a full featured opto-coupler controller, incorporating a 1.5% reference, a transconductance error amplifier and a 10mA opto-driver. Power good monitoring and output soft-start/overshoot control are also included. 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 VIN 18V to 72V 4.7µF × 3 100k UVLO_VSEC 5.9k VIN 100nF 2.2µF 100V 4:4 •• 100nF 6.8µH 2k FSW OVLO AOUT 1.82k LT3753 10k 2k 1.78k FG CSW LT8311 CSP FB 71.5k 49.9k 240kHz IVSEC RT 31.6k SYNC SOUT TAO TAS TOS TBLNK GND SS1 OUT ISENSEP OC ISENSEN INTVCC COMP SS2 FB 34k 0.47µF 1µF 2k 100k 10pF 100k 6mΩ 4.7µF 100Ω 1µF 1.78k 1.5k 15nF 2.94k CG VIN CSN PGOOD OPTO COMP INTVCC SYNC PMODE SS TIMER GND 124k 1µF 1k 2.2nF For more information www.linear.com/LT8311 20k 2.2nF 100k 68pF 22µF ×2 VOUT + 12V 470µF 11.3k 100k VOUT 4.7µF 2.2µF 8311 TA01 8311f 1 LT8311 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 VIN BIAS SUPPLY..............................................................


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