SLUSE14A December 2020 – February 2021 BQ76942
The BQ76942 device supports detection of a broken connection between a cell in the pack and the cell attachment to the PCB containing the BQ76942 device. Without this check, the voltage at the cell input pin of the BQ76942 device may persist for some time on the board-level capacitor, leading to incorrect voltage readings. The Cell Open Wire detection in the BQ76942 device operates by enabling a small current source from each cell to VSS at programmable intervals. If a cell input pin is floating due to an open wire condition, this current discharges the capacitance, causing the voltage at the pin to slowly drop. This drop in voltage eventually triggers a protection fault on that particular cell and the cell above it. Eventually, the voltage drops low enough to trigger a permanent fail on the particular cell and on the cell above it.
The Cell Open Wire current will be enabled at a periodic interval set by configuration register. The current source is enabled once every interval for a duration of the ADC measurement time (which is 3 ms by default). This provides programmability in the average current drawn from ≈0.65 nA to ≈165 nA, based on the typical current level of 55 µA.