LDO Regulator Application Note

The Reverse Current Protection Circuit stops the reverse current from VOUT pin to VDD pin or to GND pin when VOUT becomes higher than VIN.
Usually, the LDO using Pch output transistor contains a parasitic diode between VDD pin and VOUT pin. Therefore, if VOUT is higher than VIN, the parasitic diode conducts in forward direction. As a result, the current flows from VOUT pin to VDD pin.
RP173x Series switches to the reverse current protection mode before VIN becomes lower than VOUT by connecting the parasitic diode of Pch output transistor to the backward direction, and connecting the gate to VOUT pin.
As a result, the Pch output transistor is turned off and the current path from VOUT pin to GND pin is disconnected. (Except RP115x)