I am currently using the BQ24079 connected to a battery with an attached PCM. We recently discovered that the PCM has solder balls that can bridge the PCM in various locations. We are trying to assess the impact of these solder balls on the BQ24079 during charging and discharging. The picture below shows the PCM circuit and the locations where a solder-ball could short based on its size and the board layout.
I am most concerned about locations 2 and 7/9, but I am interested to hear your opinion. I've described my understanding of what would happen below, so please let me know if I misunderstand anything.
- Position 2: This would short the cell through R1 (330 Ohms) and present a 12mA load on the circuit. My understanding is that this would increase the "battery" current sent out from the BQ24079 and affect charge termination. Currently, the device terminates when the battery current is 50mA, but in this case, the actual battery current would need to decrease to 38mA to account for the 12mA load through R1.
- Positions 7/9: A short across both of these would show up as a series resistance in line with the battery and the BQ24079. If the resistance was large enough, it would show up as a voltage drop in series with the battery and cause the BQ24079 to misread the battery voltage. For instance, if the battery voltage was 3.5V and the resistance was 1 Ohm, a 500mA charging current would mean the BQ24079 would see a "battery voltage" of 3.5 + (0.5)(1) = 4V. In this case, the BQ24079 would enter constant voltage mode earlier and the series resistance would essentially limit the current going into the battery.
