This document introduces FAN6208, which is a synchronous rectification controller for isolated LLC or LC resonant converters that can drive two individual SR MOSFETs emulating the behavior of rectifier diodes. FAN6208 measures the SR conduction time of each switching cycle by monitoring the drain-to-source voltage of the SR MOSFETs.
The document introduces the FAN6208, a synchronous rectification controller designed for isolated LLC or LC resonant converters. It explains how the device drives two individual SR MOSFETs to emulate rectifier diodes, reducing conduction loss and improving efficiency, particularly in low output voltage applications. Key features include adaptive timing based on drain-to-source voltage monitoring and a Green Mode to minimize power consumption at light loads.
The note provides detailed design guidelines, including typical application circuits and timing diagrams. It covers the configuration of the DETL pin for low-voltage detection, the RP pin for programming dead time and selecting operating modes, and the gate-shrink functions that prevent shoot-through during load transients or fast switching frequency changes.
| Turn-on delay | about 350ns |
|---|---|
| DETL pin low detection threshold | 2V |
| DETL pin allowable voltage range | -0.3V to 7V |
| DETL internal current source | 50uA |
| RP pin internal constant current source | 41.5uA |
The FAN6208 turns on the MOSFET after approximately 350ns once the DETL voltage drops below 2V.
The dead time can be programmed using a resistor connected to the RP pin.