Do you mean the VREFDDR output of the PMIC? If so, please specify some more details. What voltage is applied to VINREFDDR? How VHALF is connected? Please provide the schematic of the PMIC connections.
The MMPF0100 PMIC doesn't have any internal mechanism to control the VREFDDR voltage, it can only be enabled/disabled internally. In normal conditions (all external circuits are connected correctly), the VREFDDR voltage is exactly the half of VINREFDDR. So, in your case, most likely there is some external side effect e.g. voltage leakage or short circuit. Please check. Also, check whether the VREFDDR voltage is enabled in the VREFDDCRTL register (bit 4 should be 1) of the PMIC.
