BQ76930: what will happen if the disconnection between the VCx and battery pack when bq76930 is running, especially VC5? does it cause any problems?

Hi Gao,

Generally an open wire to a cell input will allow the cell input to drift down.  The upper cell will develop a high voltage which limits in the 6 V range and the lower cell will drop.  These will depend on the voltages of the cells when the condition occurs. Input leakage current can vary, as can board conditions, so the change may vary with input to input or part to part.

At cell 5, or the cell going to VC5X, VC5, and VC5B, VC5 is a power pin.  The part has the dINOM and dIALERT currents shown in the data sheet.  If the host is quick to clear the ALERT condition when set dIALERT may result in a low effective current, but it likely that the board node will drop with "cell 5" reading a low voltage and "cell 6" reading a higher voltage. VC5X will be pulled by the temperature measurement of the thermistors as well, so depending on the difference in the 2 thermistors VC5X and the cell voltages could be pulled up or down.

In any of these situations the part may detect an OV or UV.  If the voltage were low enough OV may not occur, if the voltage drops quickly below UVMINQUAL the low voltage may not be recognized as a UV.  The host may need to recognize and respond to this condition.