SLVSAF7C September 2010 – April 2019 TPS61251
The device has a built-in power good function to indicate whether the output voltage has reached the programmed value and therefore the capacitor is fully charged. The power good output (PG) is set high if the feedback voltage reaches 95% of its nominal value. The power good comparator operates even in shut down mode when EN is set to low and/or VIN is turned off. This guaranties power good functionality until the capacitor is discharged. The PG output goes low when VOUT drops below 2.3 V and indicates the discharge of the capacitor. If the output voltage decreases further and goes below 2 V the converter disables all internal circuitry. Therefore the PG open drain output becomes high resistive and follows the voltage the pullup resistor is connected to.
Because power good functionality is active as long as the output capacitors are charged the converter can be disconnected from its supply but is still supplying the following circuitry with energy. A connected buck converter or buck-boost converter can use this energy to support a follow-on circuit that needs additional energy for a secured shut down.