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BQ76942: High balance current using external FETs?

Ben Adamson
Prodigy 100 points
Part Number: BQ76942

I am planning to develop a battery balance charger which will only be connected to the cells when charging, meaning there is very limited time to achieve balance. With this in mind I would like to reduce external balance resistors to 10 ohms, to achieve 0.42A balance current. Of course I will use power resistors and rated FETs.

Would there be any issues in doing this? Would I need to change anything from the example external balance circuit? Or perhaps would a different IC be recommended for battery balance / overcharge protection?

  • 0
    TI__Guru* 81035 points

    Hi Ben,

    Sorry for the delayed response. We've been experiencing power and internet outages in our area due to the snowstorm.

    The minimum cell input resistor value for this device is 20 ohms. I assume you are are talking about the balancing resistors for the external FETs. In this case 10 ohms should be fine. You can use multiple resistors in parallel to help with power dissipation. Using 100 ohms for the cell input resistors (max recommended) will help to generate enough VGS voltage for the FET. You will need to select a FET with RDson defined at a low enough VGS.

    If you need to balance at lower cell voltages, generating a high enough VGS for the FET (depending on which FET you are using) may become more of a challenge. In this case BJTs might be more practical. The math gets a little trickier though.

    Best regards,

    Matt