Secondary-Side Synchronous Rectifier Driver

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

* 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