I am using two UCD90120A power monitors on a board. One power monitor controls my standby rails which sequence on initial power up, and the other controls the local rails which sequence when given a command from an FPGA to begin sequencing. I have the PMONs configured such that GPIOs go between the two to indicate when the Standby rails have all reached POWER_GOOD state and when the Local rails have all reached POWER_GOOD state. I use this to control sequencing and desequencing. The Local rails can only sequence when all Standby rails have reached POWER_GOOD. The Standby rails can only desequence when all of the Local rails are no longer POWER_GOOD. Under normal operation this works very well. I discovered recently though that I cannot shut down my Standby rails if they fault. If a Local rail faults, both the standby and local rails shutdown. However, if a Standby rail faults, the fault log indicates a fault and slaves all necessary rails but does not actually disable power on any of the rails. I found that if I remove all signals between the two PMONs, then the fault behavior is normal. So it seems to me that the Standby is waiting for the normal desequence command to begin shutdown in a fault condition. I tried to fix this by using another GPIO to indicate to the Local PMON when a fault occurs on the Standby PMON so that the Local will shutdown and then allow the Standby to shutdown. However, when I set my GPO to go high if there was an overvoltage fault on one of the rails, it would not change states even when I induced the fault on that rail and the logs recorded that fault. I believe it was because the rail was still enabled since it was still waiting on the signal from the other PMON.
I am wondering if there is any way to create this communication both ways between the two PMONs in the case of a fault or to cause the Standby PMON to only wait on the signal from the Local PMON to desequence in normal conditions and not in fault conditions?
Thank you!
