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BQ76952: Accuracy of Current Measurement

Keith Keller
Expert 7230 points
Part Number: BQ76952

Hello,

What would be the accuracy of the current measurement of the bq76952 with a 1 mOhm sense resistor?  For different sample rates?

Thank you, Keith 

  • 0
    TI__Mastermind 42060 points

    Hello Keith,

    The accuracy would be dependent on the offset error and current resolution. The offset voltage error is ~7.6-uV, so with a 1-mOhm sense resistor, you would have ~7.6-mA in offset error. Now on-to the resolution of the device, assuming ideal conditions of 16-bit range across the -0.2-V to 0.2-V coulomb counter range, the voltage resolution would be ~6.1-uV, with your 1-mOhm sense resistance the current resolution would be ~6.1-mA.

    Best Regards,

    Luis Hernandez Salomon

  • 0 in reply to Luis H. S.
    TI__Expert 7230 points

    Hello, 

    Do both of the errors add together to give a total maximum error of 7.6 + 6.1 = 13.7mA?

    Thank you, Keith

  • 0 in reply to Keith Keller
    TI__Mastermind 42060 points

    Hello Keith,

    No, they are different. The offset error would mean that even at no current you may be able to read a ~7-mA current on the device. The current resolution is not an error, it is each current step that could be measured. This means that it would not be able to measure any currents smaller than ~6.1-mA and the current will be quantized in ~6.1-mA steps. 

    What currents are being expected in your system? At very high currents there are some other current error considerations. Assuming worst-case error conditions, a 200-A current across a 1-mOhm sense resistor could see current errors of up-to ~1.539-A (0.77% Error).

    Best Regards,

    Luis Hernandez Salomon