I have a lot of bulk cap on this rail and the operation is set to "ON". This issue happens when we use the PMBUS operation command to turn on the VR. We don't use the EN pin, or in other words the ON/OFF register is set to 0x1B.
My guess is that since there is a lot of bulk cap, and the load device draws almost no leakage current, when the regulator is already ON, our SW tries sends the OPERATION command to power on the VR even though it is already on. I am guessing that every once in a while the UC is so low that it triggers this UC fault.
I would like to know if I can set the UC lower? I don't see it as an available register.
Here is what I get when I poll for the voltage under normal operation:
OFF:
VDD Output voltage = 0.007812V
VDD Input voltage = 5.0547V
VDD Output current = -0.0964A
ON:
VDD Output voltage = 0.896484V
VDD Input voltage = 5.0312V
VDD Output current = -0.4673A