The intent is that C29, in parallel with R27, should hold V- at ~3.1 V even if 3V3 has a short glitch. So a quick glitch on 3V3 should be detected by the comparator and trigger an output which I can read with additional circuitry.
After testing a few PCBs and seeing initial input current spikes and some minor smoking from the board, I've narrowed it down to this chip as a possible culprit. I started taking voltage measurements and saw big disparities in V-: 0.96, 2.82, 1.58, 1.32, 3.96?? Seems like this chip is just completely fried, but I'm not sure why this would have happened.
Does anything stick out as an obvious mistake? Some thoughts/notes:
I noticed the same input current jump when I applied only 3V3 to the board, without any power on 5V.
Without desoldering the resistors from the board, I can't accurately measure the individual resistor values because of the rest of the board.
Think I got to the bottom of it. I think the chips were actually still operational, and the smoking/initial current surge was coming from somewhere else (to be determined where). The actual problem had to do with my biasing circuitry for V-, and the comparators actual bias voltages.
Considering the wide range of possible comparator bias currents, this could definitely explain the difference in V- readings I was seeing. For my next round of PCBs, I'll spec the ideal biasing current to be in the 10-100 uA range so the comparator bias current becomes insignificant.
Does this make sense?