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BQ76925EVM: Incorrect voltage measurement

Travis Miller34
Prodigy 30 points
Part Number: BQ76925EVM

I am having voltage reading problems on my BQ76925EVM. I am using the example code and just converting the ADC values to voltages as explained in the datasheet. I am measuring the voltages of a 6 cell LiPo battery. I have found that Cell 1 is consistently measuring lower when compared to a multimeter, measuring about 0.15V lower. The other five cells measurements match up to the multimeter. This has occurred over multiple batteries.

Is there any explanation to why this is happening?

  • 0
    TI__Guru 54715 points
    Hi Travis,
    Look for a loss between BATT- and Cell0. They are different connections on the EVM. You can connect the 2 with the Cell 0 switch for the cell simulator, but there may be a voltage drop across the switch.
  • 0 in reply to WM5295
    Prodigy 30 points

    To follow up:

    There was no voltage drop between BATT- and Cell 0. Also, I have several of these chips and each one acts differently. One might have cell 5 be off and another cell 6. What could be the cause?

    I know there is offsets that are set at the factory. I am trying to calibrate those to see if they better match the multimeter. Could the factory set offsets need to be changed depending on the battery used, or for any other reason etc? It is a 12000mAh LiPo.

  • 0 in reply to Travis Miller34
    TI__Guru 54715 points
    Hi Travis,
    Each cell input has individual characteristics, that is why each has individually stored gain and offset. The calibration is based on approximately matching cells, so you will see comments in the forum that the calibration is not so good when using cell 6 as cell 5, the actual range of the input is different.
    A few mV on cell 5 or cell 6 or others sounds like it could be calibration. The 150 mV low on cell 1 sounds like a lot for calibration. Certainly apply the stored calibration correction to check it. If there is not an offset on the board there is likely damage to the IC.