Tool/software:
I am trying to use CTRD to shut down the system when the battery gets below a certain voltage after a time delay (using the BQ77915's UV threshold as a failsafe) and I'm trying to use an optocoupler to preserve ground isolation. The shutdown signal is active low, so under normal conditions the optocoupler is conducting and pulling CTRD low. I put a 10M pull-up resistor on CTRD (connected to VBAT) so when the optocoupler turns off I would expect CTRD to rise to VBAT and disable the FET. That doesn't seem to be happening, though. I checked it with an oscilloscope and CTRD is only rising to 1.2V, which is not enough to disable the FET. I reduced the resistor to 1M, which pulled CTRD to 7V, but I'd like to know what's going on here so I don't encounter any unexpected edge cases. Is there a reason a large pull-up resistor wouldn't pull CTRD all the way to VBAT if there's no other viable current pathways?
