AP3917COperation DescriptionOverall Introduction The AP3917C is a universal AC input step-down power switcher. Peak current and switching frequency reduce as the load decreases, so the device can get excellent efficiency performance at light load and improve the overall system efficiency. Coordinating with an external single- winding inductor can achieve a low BOM cost solution. VBP Waveform and ON/OFF Control The AP3917C control circuit power supply voltage VBP is charged by the internal high-voltage regulator. When the BP voltage is charged to T VBP_HVOFF (8.5V), the IC starts up, and the internal high-voltage regulator is turned off. When the BP voltage drops below VBP_HVON (8.2V), the C internal high-voltage regulator turns on again to charge the external BP capacitor. U DO R When fault conditions happen, such as some protections like overload faults, short-circuit faults, over temperature faults, and open-loop faults, P the AP3917C stops switching. Afterwards an internal current source IBP_LATCH discharges the external BP capacitor. The internal high-voltage