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BQ35100: The sense resistor value design

Paul Yeh
Genius 16145 points
Part Number: BQ35100

Hi team,

Customer would like to reduce current sense resistor value from 100mohm to 10mohm, is it ok?

Any side effect here? what accuracy difference between 100mohm and 10mohm?

And what min resistor value they can use?

Thanks

  • 0
    TI__Guru 52115 points
    See Section 8.2.2.5 of the bq35100 datasheet about how to calculate the ideal value of the sense resistor.
    Andy
  • 0 in reply to Andy Liu (BMS)
    TI__Genius 16145 points

    Andy,

    Of course, I know this equation. But please read my question carefully.

    If customer would like to use smaller sense resistor, is it ok or not?

    for example: if customer's peak load current is 1000mA and they use 100mohm currently, so Vmax is 100mV, it should be ok.

    But based on the same loading (1A) but they would like to reduce sense resistor voltage drop, how low they can use? any side effect.

    This is my question. Thanks

  • 0 in reply to Andy Liu (BMS)
    TI__Genius 16145 points

    Andy,

    Of course, I know this equation. But please read my question carefully.

    If customer would like to use smaller sense resistor, is it ok or not?

    for example: if customer's peak load current is 1000mA and they use 100mohm currently, so Vmax is 100mV, it should be ok.

    But based on the same loading (1A) but they would like to reduce sense resistor voltage drop, how low they can use? any side effect.

    This is my question. Thanks

  • 0 in reply to Paul Yeh
    TI__Guru** 105600 points

    Hello Paul,

    The accuracy of the gauge to sense small currents is reduced with a smaller sense resistor. Depending on how much smaller it could effect the gauging. If they are not planning to be using the gauge with small loads this may not be an issue. 

    You can check the minimum current the gauge can sense by looking at the coulomb counter ADC input range (-125mV to +125mV) and the bits of resolution (14 min, 15 max) and using Ohms equation to see if the accuracy is high enough for the application.

    Sincerely,

    Wyatt Keller