The FSD22A has an integrated high-voltage starting circuit, and the SW pin provides charging current to the VDD power supply when starting. When the VDD voltage reaches VSTART, the internal high voltage start circuit is closed, and the energy of the VDD capacitor is provided by the converter. When the VDD voltage is lower than VSTOP, the chip will not restart immediately. Only when the VDD voltage is low to VRST, the high voltage start tube will open and charge the VDD capacitor. Until the VDD voltage reaches VSTART.