FAN6248HCMX

The FAN6248HCMX from onsemi is a highly integrated synchronous rectifier controller optimized for LLC resonant converter secondary-side rectification. It uses an adaptive virtual turn-off threshold scheme with a 16-step offset voltage modulation to precisely time the SR MOSFET turn-off, minimizing body diode conduction time and maximizing efficiency. The controller supports both high-side and common-mode SR MOSFET configurations. Its predictive gate drive capability anticipates the zero-crossing point of the SR current, enabling near-ideal diode emulation in the variable-frequency LLC operating regime.

The FAN6248 monitors the drain-source voltage (VDR) of the SR MOSFET to detect current direction. When the secondary-side current begins flowing through the body diode (VDR negative), the controller turns on the SR MOSFET. The turn-off timing is determined by the adaptive virtual turn-off threshold: a 16-step offset voltage is modulated to compensate for parasitic inductance and MOSFET RDS(on) variations. If the dead time between SR turn-off and primary switch turn-on exceeds 200ns, the offset decreases by one step in the next cycle, reducing the dead time. This closed-loop adaptation ensures optimal SR timing across load and line conditions.

• LLC resonant converter secondary-side synchronous rectification
• 80Plus Titanium server power supply SR stages
• High-density AC-DC adapter and charger platforms
• TV and LED display power supply SR control
• Industrial DC-DC converter output rectification