The SY22812B is a high frequency quasi-resonant (QR) flyback controller designed for PD adaptors and quick chargers. It can drive enhancement GaN FETs directly, and can deliver 240W output power over a wide output voltage range. The 25kHz–300kHz switching frequency allows for reduced transformer and capacitor sizes.
The SY22812B operates using peak current control. It provides a QR mode in which the GaN FET can be turned on at a valley point to reduce switching loss, especially under high input voltages.
In conventional QR flyback solutions, the valley number always varies between 1 and 2 or 3 and 5, which increases VO ripple and creates audible noise. The SY22812B uses a proprietary circuit to lock the valley number between 1 and 6, for improved stability compared with other conventional QR solutions.
If the load decreases, SY22812B will enter discontinuous conduction mode (DCM) to reduce the switching frequency for higher efficiency. If the load is very light, the SY22812B will enter burst mode to reduce power loss.
The SY22812B provides comprehensive functions to ensure reliable operation, including: HV startup, X capacitor discharge, brown-out protection, output and VCC overvoltage protection (OVP), output undervoltage protection (UVP), internal and external overtemperature protection (OTP), and open-loop protection (OLP).
It is recommended to use the SY23434 as a secondary side Synchronous Rectifier (SR) controller in conjunction with the SY22812B so that Zero Voltage Switching (ZVS) operation can be achieved for higher efficiency.
The SY22812B is available in a SSOP9 package.
