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BQ78350-R1: bq78350 and bq76940 SOC accuracy

Ansul Tyagi
Intellectual 305 points
Part Number: BQ78350-R1
Other Parts Discussed in Thread: BQ76940, BQ78350, , GPCCEDV

Hi,

I wanted to know what is the accuracy of SOC estimation done by bq78350 and bq76940 ?

  • 0
    TI__Guru* 81034 points

    Hi Ansul,

    SOC accuracy for a CEDV battery gauge depends on how well you characterize your battery to tune the CEDV parameters and whether your battery will periodically discharge to 7%. Accuracy of 2-3% is very common for many applications. Some other TI battery gauges use the Impedance Track algorithm which has the potential for better accuracy (~1%). However, I have seen users achieve 1% accuracy with CEDV gauges with enough iterative tuning.

    For more information about setting up the BQ78350-R1 gauging parameters, see this app note: http://www.ti.com/lit/an/slua924/slua924.pdf

    Best regards,

    Matt

  • 0 in reply to Matt Sunna
    Intellectual 305 points

    Hi Matt,

    Thanks for the message.

    Do you have any example or document on how to characterize the battery to tube CEDV parameters.

    I have the Li-ion cell datasheet.

  • 0 in reply to Ansul Tyagi
    TI__Guru* 81034 points

    Hi Ansul,

    The app note I pointed to before references the GPCCEDV tool. The instructions for this tool are here: http://www.ti.com/lit/ug/sluub45b/sluub45b.pdf

    Basically, you need to collect 6 discharge logs for your battery (2 different loads, 3 different temperatures). This will generate CEDV parameters to ensure accuracy over different load and temperature conditions.

    Best regards,

    Matt

  • 0 in reply to Matt Sunna
    Intellectual 305 points

    Hi Matt,

    Thanks for the response.

    Can I calculate CEDV coefficients my self by using the tool or I need to send the data to TI?

    Is CAS number of the cell also required (Chemical Abstracts Service) ?

  • 0 in reply to Ansul Tyagi
    TI__Guru* 81034 points

    Ansul,

    Yes, you can calculate the CEDV coefficients yourself using the GPCCEDV online tool. Use the instructions in the Gas Gauging section of this app note (http://www.ti.com/lit/an/slua924/slua924.pdf) and the GPCCEDV tool instructions: http://www.ti.com/lit/ug/sluub45b/sluub45b.pdf

    Number of cells is one of the required inputs for the GPCCEDV tool. 

    I think there must be some confusion - Chemical Abstracts Service is not part of setting up this gauge. Are you thinking of the ChemID? TI has a ChemID database that contains a large number of batteries that have been characterized in TI's battery characterization lab. The app note shows how to select the ChemID for your battery. The BQ78350-R1 only uses the ChemID when it powers up or comes out of Shutdown to do an initial capacity estimation, but it is not used during normal operation.

    Regards,

    Matt