We have a product in production using BQ25708. We are using a 12 Volt lead-acid battery.
The CELL_BATPRESZ pin is connected to the battery via a resistor-divider such that a 12 volt battery applies about 5 volts to CELL_BATPRESZ. (This indicates 4 cell battery configuration.)
Normally this functions as desired. The problem occurs when:
- There is a power loss
- The battery becomes completely depleted and the system shuts down
- Power is restored
- The depleted battery applies a low voltage to CELL_BATPRESZ at power up. This indicates a 1 cell battery configuration. (We need it to be 4 cell configuration!)
- Firmware sets the VSYS (MinSystemVoltage register) to 12 volts
- The BQ25708 thinks this voltage is too high and asserts SYSOVP and goes into shutdown
- We can't recover without removing power, but there is no physical access to the device. BIG PROBLEM!
The question is: Is there any way, through registers, to change the SYSOVP limit? We understand that we should connect the CELL_BATPRESZ pin differently, but we already have product with customers. We are hoping to fix this through a firmware update to our product. Surely there mus be a register or something that allows us to change the SYSOVP limit... can you please help?
Thanks you!
-Mike
