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BQ76972: Stacked design bring-up wrong cell measurement

Ronan Chauvin
Prodigy 222 points
Part Number: BQ76972

Tool/software:

Hello TI Team,

During the bring-up of a design similar to the TIDA 010247, we are encountering an issue with the cell measurements.

The implemented design has x2 BQ with the possibility to connect from 3 to 10 cells each (24V->72V).

When acquiring the BQ data, the two first cells of the bottom BQ have wrong voltages (-0.1V, 0V and 1.3V instead of an expected 2.1V for example). The first cell of the top BQ has wrong voltage (1.2 vs 2.1V).

All other cell voltages are good. We tested the measurement on real cell and simulated cells. Using a multi-meter the cells voltages are measured with the same values.

Do you have an idea of what could explain this behavior?

Thanks,
Ronan

Here are some screenshot of our design:



VC0 and GND looks to have a ~0.8V offset.





  • 0
    Prodigy 222 points

    Found it.

    It is due to the fact that the design is split on two boards and when not having the power board, the VC0 (Current+) is not linked to GND (via 0Ohms R2 on the picture attached) leading to incorrect cell voltage measurements.

    Sorry for the noise.

    Thanks,
    Ronan