SLUUBT5C November 2018 – June 2021 BQ40Z80
The gauge forces RemainingCapacity() to 0 mAh when the battery stack voltage reaches the Term Voltage for a period of Term V Hold Time. If IT Gauging Configuration[CELL_TERM] = 1 or 0, the battery can terminate based on either cell voltage or battery stack voltage. When the cell-based termination is used, the Term Min Cell V threshold is checked for the termination condition. The cell-based termination can provide an option to enable the gauge to reach 0% before the device triggers CUV for a pack imbalance.
However, there may be scenarios where (when using cell-based termination), due to varying cell interconnect differences, EDV detection could happen earlier than necessary. For example, if Cell 1 and Cell 3 have 0-Ω cell interconnect, while Cell 2 has 200-mΩ interconnect, Cell 2 would always cause EDV detection early because it has 200-mΩ extra resistance to it, while the cell itself was actually not that low.
A solution to handle this potential premature cell-based EDV detection is to use the Cell 1..7 Interconnect Resistance (values entered by the user) to calculate the related IR drop and adjust in firmware either the Term Min Cell V (or measured cell voltage) when doing the comparison of Term Min Cell V to cell voltages, thus preventing premature EDV detection. This choice to “add back” the interconnect related IR drop to the cell voltage (or lower the Term Min Cell V) can be made optional with a configuration bit [CELL_INTER_IR]. Additionally, IT simulation would also need to include this IR drop in the calculation so that the simulation does not estimate the EDV too early.