Hello
I have some packs that were setup on a charger (power supply) set to 16.8V, but the pack charge cutoff was 16.4V. The BQ20z45 protected itself when the voltage got to 16.4V, but was unresponsive after that (couldn't communicate with BQ software). Additionally, since the FETs were off this allowed the power supply to go back up to it's open circuit voltage (could be up to 50V). After opening the pack, we found that the physical component (BQ20Z45) was getting hot, as well as the diode on the input to the BAT pin. This was an indication that the unit was drawing power through this BAT pin. At the time, the 2.5V rail was still functioning properly, didn't check the 3.3V rail. I removed the top cell in the stack (VC1) to shut down the IC and start measuring pins for short circuit (assuming that the open circuit voltage may have damaged something). When I couldn't find any, I powered back up to try to read the 3.3V internal regulator. After "jumping the FETs", the system powered up and worked fine, nothing was getting hot and everything was communicating as expected.
I am trying to determine what may have gone wrong as I can't open these packs in the field. Any reason why this would shut down? Why would the BAT pin be drawing power?
Thanks, Mike
