When turned on, a flyback converter starts with 0V output voltage. This can cause the feedback voltage FB to clamp to its max. value and trigger overload protections. To prevent this from happening, the UCG28826 starts in soft start mode. During this time, an internal FB voltage ramp increases in eight steps from 0V to max. value in 4ms. The max. value of internal FB ramp is at FB pin voltage equivalent of 80% of I_PK,MAX setting and changes for different resistor settings on IPK pin. During this time, the smaller of this internal ramp voltage and actual FB pin voltage is used to determine the device operating point in the control law of Figure 6-4. Once the internal FB ramp voltage reaches the max. value is when control is transferred to FB pin voltage for output regulation. Soft start sequence is executed every time at start up or when recovering from fault (auto-retry or latch) and brown-out conditions. The minimum frequency clamp is changed to 10kHz only during soft start (which is otherwise at 25kHz during normal operation). This helps at startup when valleys are missing and the control law forces turn-on of primary GaN HEMT every 10μs from the last turn-on edge (if valleys are missing), to charge the output capacitor.