MAX6399 - Undervoltage Lockout Not Working

[waymond91]

I have a circuit using the MAX6399 acting as an over-voltage and under-voltage lockout.
Here is a link to the part: https://www.digikey.com/en/htmldatasheets/production/2916090/0/0/1/max6399
I had one small hiccup where I got the gate pin wrong on the pcb, but I have bodged a to-220 onto the pads.

I was targetting an overvoltage lockout at 14.4V, and undervoltage at 11.6V. However, the overvoltage kicks in near 13.7V, and the undervoltage never fires.

I can measure the "OUT" and "OUT_SET" threshold voltages as I adjust the supply and see they are near their respective thresholds at the appropriate voltage.
For example, the undervoltage is near 0.5V at 11.6V, and the overvoltage is near 1.23V at about 14.4V

We had this behaviour after replacing the mosfet but before replacing the MAX6399. I have since replaced the max6399 and get the same behavior.

The Schematic


3D Board


Board with bodge mosfet AKA "The Bodgefet"

[waymond91]

For posterity - the undervoltage cutoff seems to only be hooked up to the ~POK pin and not the GATE pin of the IC