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BQ25790: ADC Accuracy

Part Number: BQ25790
Other Parts Discussed in Thread: BQ25970

The BQ25970 datasheet specifies only range and resolution for each ADC reading type, but no accuracy numbers are provided.

What is the expected accuracy of the ADC readings (especially for the currents)? 

  • Hi Alex,

    The accuracy is not great at about +/= 25% over temp with about a +50mA dc offset for the 13-15 bit settings.  The 12-bit setting will always read low and is not recommended.  

    Regards,

    Jeff

  • Hi Jeff, 

    Thanks for the tip.

    And what is the ADC accuracy for the voltage rails: VBUS, VBAT, etc?

  • Alex,

    The voltage rail accuracy is slightly better but has a similar +50mV offset.

    Regards,

    Jeff

  • Hi Jeff,

    I was under impression that the low accuracy of the current sampling is due to inaccurate I->V conversion, which should not be an issue with direct voltage sampling. 

    I expected the voltage sampling accuracy to be mostly a combination of bandgap accuracy (which seems to be 0.5% based on the voltage regulation tolerance figures) and the matching accuracy of the internal sampling capacitors (probably few %).

    The 50mV offset is not a problem for me, but if you're saying the overall accuracy is slightly better than +/-25% then I'm a bit concerned. It means that when sampling a 2S battery voltage of 7V the reading might say anything between 5.25V and 8.75V, which is a pretty wide range when it comes to battery voltage. 

    A gain error of 1% or 2% would seem like a more reasonable accuracy figure. The sample that I'm testing seems to be pretty accurate when it comes to voltage sampling, but I did not test it at different temperatures.

    Can you please double-check? It's very important for my design.

  • Hi Alex,

    The charger doesn't use the ADC for regulation.  The ADC is only for a reasonableness check.  Unfortunately, I don't have accuracy data that I can warranty.  The above numbers were derived from measurement taken on a few units over temp but not a true statistical sample.  

    Regards,

    Jeff