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BQ78350-R1: Program Battery Chemistry

Marco Antonio Vega
Intellectual 365 points
Part Number: BQ78350-R1
Other Parts Discussed in Thread: BQSTUDIO, BQ78350

Hello,

We have designed a battery pack + BMS based on reference TI Design TIDA-00792 but modified+dimensioned according to our application. In our design we use a battery pack of 14 series cells of 3,7V.

The cells used are from Yuntong supplier. In the list of Chemistry Programming cells of bqStudio, it doesn't appears (I've already updated these cell's list without success). So, at the moment I've choosen the most similar cell Chemistry ID that I've found. 

I've seen the document SLVA725A - "Simple Guide to Chemical ID Selection Tool (GPC)". Initially I thought that it was intended for creating my own Chemistry ID, but as fas as I've finally understood it's more related for the gas gauging impedance track algorithm. In our case we are using CEDV.

Are there any way/procedure for creating my own Chemistry ID to be programmed? Or I've to continue developping with most similar chemistry ID that I've found for my cells. 

Regards,

Marco

  • 0
    TI__Guru* 81034 points

    Hi Marco,

    The BQ78350 is unique in that it is a CEDV gauge, so the ChemID is only used when the device powers on or after a reset to estimate the SOC initially. ChemID selection is much more critical for Impedance Track gauges. So using the closest match is the best way to go.

    For the best gauging accuracy, you will need to configure the CEDV gauging coefficients. The instructions for this are available in the Using the BQ78350-R1 document in the Gas Gauging section. Once you configure the CEDV coefficients, you will want to set the EDV_CMP bit to '1' in the CEDV Gauging Configuration register.

    Best regards,

    Matt

  • 0 in reply to Matt Sunna
    Intellectual 365 points

    Hi Matt,

    Thank you for your fast response. Ok clear!

    Just a couple of questions more:

    1. I've done already the 6 test high/low rate + temperature and I've got the report response. In this report appears this parameters:

    VOC75 55094
    VOC50 53319
    VOC25 52529

    Where should be them introduced? The rest of params reported are all clear and already introduced, but those 3 no idea... Do you know it?

    2. I've done various test with the reported parameters (with EDV_CMP=1) and I've seen as first feedback that "Gauging Status" EDV2 is set when the cells reach to the nominal cell voltage which is 3,7V. Contsequently RSOC and ASOC are updated inmediatealy to 7%, but this is not true.. In this situation, I estimate that it should be around SOC=40%. As far as I know this EDV2 is calculated by CEDV algorithm, rigth? Do you have any idea about what could be wrong? I'll log a complete discharge cycle with RSOC and ASOC using CEDV params and I'll send you for better details.

    Regards,

  • 0 in reply to Marco Antonio Vega
    TI__Guru* 81034 points

    Hi Marco,

    For the VOC75, VOC50, VOC25 parameters, these are not needed for the BQ78350. These parameters are required by some other devices.

    For the EDV2 triggering early, this is a common issue when you are first getting things set up. The best thing to do is to collect a log file using BQStudio if possible so that you can see the status of all of the registers during the discharge - this will help determine what caused the EDV2 to trigger. Some things to look for:

    • If your load has high current pulses, it can trigger a false EDV2. This can be addressed using the Overload Current parameter or the EDV2 Hold Time parameter to reduce the likelihood of false triggers.
    • Check the ExtAverageVoltage measurement. If this is not calibrated or something is not set correctly, it could be measuring different from the cell voltages and can trigger EDV2 if the gauge is configured to use the average cell voltage.

    Best regards,

    Matt

  • 0 in reply to Matt Sunna
    Intellectual 365 points

    Thank you Matt. 

    I close this issue and I open a different one related with CEDV params ;-)