LT8309

PRODUCTION

Secondary-Side Synchronous Rectifier Driver

Data Sheet (Rev. B) Product Selection Table
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Overview

  • Works with DCM and BCM/CrCM Conduction Mode Flyback Topologies
  • VCC: 4.5V to 40V
  • Supports Up to 150V MOSFETs
  • 26ns Turn-Off Propagation Delay
  • Accurate Minimum On and Off Timers for Reliable Operation
  • Adjustable and Accurate Trip Point: +5mV to –30mV
  • 1Ω Gate Driver Pull-Down
  • SOT-23 5-Lead Package

The LT8309 is a secondary-side synchronous rectifier driver that replaces the output rectifier diode in a flyback topology. By replacing the diode with a N-channel MOSFET, applications are no longer restricted by the heat constraints of the output diode. The IC replicates the behavior of a diode by sensing the drain-to-source voltage to determine when the current becomes negative. The LT8309's low minimum on- and off-times help improve noise immunity.

The fast propagation delay of 26ns allows applications to operate in discontinuous conduction mode (DCM) and critical conduction mode (CrCM). The gate driver features a 0.8Ω pull-down device for fast turn-offs. The 40V VCC rating allows the part to be driven from the output voltage or the rectified drain voltage of the MOSFET. A low quiescent current of 400μA maximizes efficiency at low output currents.

Applications

  • High Output Current Flybacks
  • High Efficiency Flybacks
LT8309
Secondary-Side Synchronous Rectifier Driver
40W, 5V Isolated Telecom Supply Efficiency vs Load Current Product Package 1
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Documentation

Data Sheet 1

Reliability Data 1

User Guide 1

Technical Articles 3

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Software Resources

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Hardware Ecosystem

Parts Product Life Cycle Description
Protection Switches & Controllers 1
LT4320
LT4320-1
Ideal Diode Bridge Controller
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Tools & Simulations

LTspice 4

Models for the following parts are available in LTspice:

  • LT8309
LTspice

LTspice® is a powerful, fast and free simulation software, schematic capture and waveform viewer with enhancements and models for improving the simulation of analog circuits.

Evaluation Kits

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schematic 4
schematic 5
schematic 6
DC1961A

LT8309ES5/LT3748EMS Isolated Demo Board | 36V ≤ VIN ≤ 72V; VOUT = 12V @ 5A

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Product Details

Demonstration circuit 1961A features the LT8309, a secondary synchronous driver in an isolated, no optocoupler, flyback converter. It regulates a 12V, 5A output from a 36V to 72V input source. Output regulation is handled on the primary side by the LT3748, a boundary conduction mode flyback controller which senses output voltage directly from the primary, resulting in a simple flyback schematic with no opto-coupler.


 
DC1961A
LT8309ES5/LT3748EMS Isolated Demo Board | 36V ≤ VIN ≤ 72V; VOUT = 12V @ 5A
DC1961A Demo Board DC1961A Demo Board DC1961A Demo Board DC1961A Demo Board DC1961A Demo Board DC1961A - Schematic

Latest Discussions

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PIN TYPE specification
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LT8306 simulation issue with secondary-side synchronous rectifier
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Can LT8309 be Used in High Side Synchronous Rectification?
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