The TPS63805 and TPS63806 can operate in reverse mode where the device transfers energy from the output back to the input. If the source is not able to sink the revers current, the negative current builds up a charge to the input capacitance and VIN rises. To protect the device and other components from that scenario, the device features an input voltage protection (IVP) for reverse boost operation. Once the input voltage is above the threshold, the converter forces PFM mode and the negative current operation is interrupted.
The PG signal goes low to indicate that behavior.