The VDD pin is connected to a bypass capacitor to ground and a start-up resistance to the input bulk capacitor (+) terminal. The VDD turn-on UVLO threshold is 21 V and turn-off UVLO threshold is 8.1 V, with an available operating range up to 35 V. The USB charging specification requires the output current to operate in constant-current mode from 5 V to a minimum of 2 V; this is easily achieved with a nominal VDD of approximately 25 V. The additional VDD headroom up to 35 V allows for VDD to rise due to the leakage energy delivered to the VDD capacitor in high-load conditions. Also, the wide VDD range provides the advantage of selecting a relatively small VDD capacitor and high-value start-up resistance to minimize no-load stand-by power loss in the start-up resistor.