ON Semiconductor introduces Synchronous rectifier (SR) controllers optimized for LLC resonant converter topologies

     ON Semiconductor has introduced an advanced synchronous rectifier (SR) controller optimized for LLC resonant converter topologies. The FAN6248 requires minimal additional components, providing high energy efficiency, simplified thermal management, improved overall system reliability, and simplified LLC power supply design. The FAN6248 is an ideal solution for modern high-performance power units (Psus), where high reliability and energy efficiency are required in a small space. Typical applications include server and desktop computers, game consoles, large-screen LCD and OLED TVS, networking, telecommunications, and LED lighting.

     The device uses an advanced hybrid SR control method that combines instantaneous leakage voltage detection with previous switching cycle information. A separate 100 V rated detection input accurately detects drain-source voltages at both ends of the SR MOSFETs, supporting any asymmetry or poor coupling in the secondary windings. The FAN6248 uses this advanced control method to prevent current reversal and avoid false triggering of SR due to capacitor current spikes, providing highly reliable operation. Counterpunch control in the controller enhances the reliability of the PSU and prevents the potential damage of conducting two SR MOSFETs simultaneously.

     The FAN6248 and only two external resistors and MOSFETs make for a simple LLC converter that supports up to 800 W. Especially in noisy environments, the addition of two capacitors further enhances the stability of the system. The FAN6248 operates reliably and efficiently over a wide range of power levels, achieving the above resonant operation without voltage spikes. When unloaded, FAN6248 enters green mode and turns off. Under light load conditions, the controller pulse in green mode provides the extremely energy efficient power supply required by high energy efficiency standards such as 80 PLUS®, DoE VI and CoC Tier 2.

     The built-in adaptive parasitic inductance compensation also minimizes the bulk diode conduction due to the packaged stray inductance in the SR MOSFET, thereby improving PSU energy efficiency. There are four devices in the series; Power designers can choose the model that best suits their application based on the switching frequency (25 kHz to 70 khz or 60 kHz to 70 khz) and the level of stray inductance associated with the MOSFETs. The range is suitable for MOSFETs in TO-220, D2PAK, DPAK or PQFN packages. In addition, the FAN6248's 10.5V high-gate drive output ensures that these extremely wide ranges of MOSFETs can be driven.

     Shane Chilton, General manager, Power Conversion Solutions, On Semiconductor, said: "The FAN6248 fully addresses the needs of modern LLC power designers. Innovations such as hybrid control and adaptive parasitic inductance compensation ensure reliable and efficient operation. With only two resistors and MOSFETs to implement the most advanced LLC converter, the controller will be popular with application design engineers who require high performance."