We have a board with an imx6Q CPU that is powered by the MMPF0100 PMIC.
In normal operation when you power the PMIC (apply a voltage on VIN) VSNVS comes up. PMIC_STBY_REQ (generated by the imx6) comes up at the same time as VSNVS, then after 20 milliseconds PMIC_STBY_REQ drops and the PMIC brings up the rest of it's supplies and the imx6 boots.
Occasionally we've observed the PMIC failing to start. We traced the behavior to PMIC_STBY_REQ not droping after 20 milliseconds. Instead it stays high and holds the PMIC in a standby state.
What could cause PMIC_STBY_REQ to stay high before the CPU boots? The reference manual shows that PMIC_STBY_REQ is generated by the Clock Controller Module (CCM) but I don't understand what the CCM does on initial power up (just VSNVS power) and what needs to happen before it drives PMIC_STBY_REQ low.