LT8309 - Secondary-Side Synchronous Rectifier Driver


  • 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

Typical Application

LT8309 Typical Application
LT8309 Typical Application


The LT®8309 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.


CAD Symbols and Footprints: The downloadable Zip file below contains the schematic symbol and PCB footprints.

For complete and up to date package information and drawings, please refer to our packaging page

Part Number Package Code Temp Package
LT8309ES5#PBF SOT-23 S5 E 05-08-1635 Yes
LT8309ES5#TRMPBF SOT-23 S5 E 05-08-1635 Yes
LT8309ES5#TRPBF SOT-23 S5 E 05-08-1635 Yes
LT8309HS5#PBF SOT-23 S5 H 05-08-1635 Yes
LT8309HS5#TRMPBF SOT-23 S5 H 05-08-1635 Yes
LT8309HS5#TRPBF SOT-23 S5 H 05-08-1635 Yes
LT8309IS5#PBF SOT-23 S5 I 05-08-1635 Yes
LT8309IS5#TRMPBF SOT-23 S5 I 05-08-1635 Yes
LT8309IS5#TRPBF SOT-23 S5 I 05-08-1635 Yes

LT8309 Package Drawing

Order Info

  • Part numbers ending in PBF are lead free. Solder plated terminal finish (SnPb) versions are non-standard and special terms and conditions and pricing applies if available. Please contact LTC marketing for information.
  • Part numbers containing TR or TRM are shipped in tape and reel or 500 unit mini tape and reel, respectively
  • Please refer to our general ordering information or the product datasheet for more details

Package Variations and Pricing

Part Number Package Temp Price
LT8309ES5#PBF SOT-23 E $2.60 Yes
LT8309ES5#TRMPBF SOT-23 E $2.60 $1.84 Yes
LT8309ES5#TRPBF SOT-23 E $2.60 $1.82 Yes
LT8309HS5#PBF SOT-23 H $3.24 Yes
LT8309HS5#TRMPBF SOT-23 H $3.24 $2.32 Yes
LT8309HS5#TRPBF SOT-23 H $3.24 $2.27 Yes
LT8309IS5#PBF SOT-23 I $2.83 Yes
LT8309IS5#TRMPBF SOT-23 I $2.83 $2.00 Yes
LT8309IS5#TRPBF SOT-23 I $2.83 $1.98 Yes
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* The USA list pricing shown is for BUDGETARY USE ONLY, shown in United States dollars (FOB USA per unit for the stated volume), and is subject to change. International prices may differ due to local duties, taxes, fees and exchange rates. For volume-specific price or delivery quotes, please contact your local Linear Technology sales office or authorized distributor.

Demo Boards

Linear Technology offers many demo boards free of charge to qualified customers. Contact your local sales office or distributor to inquire about a demo board. Certain demo boards are also available for sale via credit card on this website. Demo boards are for evaluation purposes only. It remains the customer’s responsibility to verify proper and reliable operation in the actual end application.

Part Number Description Price Documentation
DC1961A LT8309ES5/LT3748EMS Isolated Demo Board | 36V ≤ VIN ≤ 72V; VOUT = 12V @ 5A $175.00
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  • High Output Current Flybacks
  • High Efficiency Flybacks

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