BQ76942: BQ76942 cell voltage disconnection test

Hello Star,

The BQ76952 has an open-wire feature to protect the pack in case of a broken cell connection between a cell in the pack and the BQ76952.

A small current source operates in periodic intervals between each cell and Vss in order to check for this. This will cause changes in the voltages of the disconnected cell and the cell above it. Albeit for a different device, you I described how the voltages get affected when an open-wire scenario occurs in the following e2e thread:

 (+) BQ77216: BQ77216 Open wire operation - Power management forum - Power management - TI E2E support forums

That thread may be useful in understanding how the voltages are affected.

For the BQ76952, the functioning would be different however, there is no direct open-wire fault or alert, instead, the disconnected cell will drop in voltage and eventually trigger a Cell Undervoltage protection fault on that particular cell, as well as a Cell Overvoltage protection fault on the cell above it. These would show in your cell measurements. You can read how the open-wire feature functions in detail and how to configure open-wire in Section 5.3.24 Cell Open Wire of the Technical Reference Manual.

The section also describes how to disable open-wire protection completely if not desired.

Hope this helped

Best Regards,

Luis Hernandez Salomon

Hello Star,

I am not exactly sure the behavior of the device if left unconnected, however, the device was designed to have the cell 1, cell 2 and cell 16 inputs always connected. Some things may not function properly otherwise, I would not be able to say what.

However, I just tested with my board the cell 1/cell2 voltage by applying an open-wire condition on cell 1. The Cell 1 voltage drooped while cell 2 voltage increased, which is what I expected. Looking at your data, this seems consistent in removing cell 1 or cell 3. So, it seems to me that the open-wire function is working as intended.

Best Regards,

Luis Hernandez Salomon