The output voltage is sensed through the bias winding (BW) voltage sense pin. With one terminal of the bias winding connected to primary side ground, the bias winding voltage at the other terminal represents the output voltage when the secondary side rectifier diode conducts. A resistor divider is typically used to connect from the bias winding terminal to the BW pin. The BW voltage is compared with a positive and a negtive threshold to generate an output OVP fault. During startup, BW pin is multiplexed for burst mode threshold programming. The details are introduced in the Soft-Start and Burst-Mode Threshold section. The block diagram of the bias winding voltage sense block is shown below.
If the OVP event is high for 5 consecutive switching cycles, the system will enter FAULT state. The actions during an OVP fault are described in the Bias Winding Over Voltage Protection (BWOVP) section.