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Reduced Accuracy of BQ76930 for CC compared with BQ2040?

Dan Bishop
Prodigy 195 points
Other Parts Discussed in Thread: BQ78350, BQ2040, BQ76930

We are looking to replace a BQ2040 with a combination BQ76930 and BQ78350. I understand that the BQ2040 uses a Voltage to Frequency front-end for charge counting which captures relative current in counts from the frequency output? As a result all peaks and valleys get captured between sampling intervals. Would that suggest that the BQ76930 (which seems to just sample voltage) will be less accurate?

  • 0
    TI__Guru 54715 points

    The bq76930 uses an integrating converter for the CC, so it will capture the peaks and valleys in the current waveform if they are in the dynamic range of the inputs.  The register will provide the most recent 250 ms, the MCU will need to capture and sum the CC samples.

    One of the gauge experts may have a better description of accuracy, but if you look at table 3 of the bq2040 datasheet, INL is shown as 1% typical.  1% applied to the bq76930 single ended CC range (2^15) would be ~ 328 lsb while the datasheet shows +/- 2 lsb typical.  So it would seem the bq76930 should be more accurate.  Gain and offset would be expected to be calibrated out in either implementation.

  • 0 in reply to WM5295
    Prodigy 195 points
    I had to look up integrating ADCs, but I see now how it works. We were always shown that this type of amplifier configuration was called an "integrator", but I never knew why. So it sounds like change in voltages during the measuring period will get registered. Thanks.