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BQ27421-G1: Difference between devices G1A, G1B and G1D

Johannes Brecher
Prodigy 110 points
Part Number: BQ27421-G1
Other Parts Discussed in Thread: GPCCHEM

Hello,

can you tell me whether the three types G1A, G1B and G1D have the same hardware?

I am guessing that these are the same devices, but that they are shipped with different pre-configurations that rely on the CHEM_ID?

If this is true: Would it be possible to use a G1A fuel gauge for a battery that is charged up to 4.3V, if the configuration of this device is changed appropriately?

Thank you and best regards,

Johannes

  • 0
    TI__Genius 14985 points
    Hi Johannes,
    Unfortunately those profiles aren't changeable so you would need to order a bq27421-G1B for your 4.3V battery.
  • 0 in reply to dMax
    Prodigy 110 points
    Hi,
    thanks for your answer.

    I created a golden image with a G1B for a 4.3V battery and programmed this to a G1A. The gauging results were quite promising. From this observation I assume that the CHEM_ID serves as a switch to select one of the three parameter settings for the fuel gauge types G1A, G1B or G1D. And it seems to me that all those parameters that are selected by the CHEM_ID can be configured via I2C.
    Is this true?

    Can you tell me in detail where these three devices differ from each other? (Hardware, algorithm, settings?)
  • 0 in reply to Johannes Brecher
    TI__Guru* 76230 points
    Hi Johannes,
    The devices differ only in the chem id. They have chems that support different max voltages. This is captured in the data sheet. You need to run our online tool gpcchem to determine if the device chem id are close enough for your cell . Like David point out, you will want to use the G1B for your 4.3V cell. The tool will give you a rough idea of how much error you expect to get using the G1B flavor.

    thanks
    Onyx
  • 0 in reply to Onyx Ahiakwo
    Prodigy 110 points
    Hi Onyx,
    thank you very much.

    So does the CHEM_ID serve as a selector for parameters in the Data Memory?
    - This would basically mean that it does not matter which fuel gauge version I use, as long as the Data Memory is configured properly.
    - Or does the CHEM_ID serve as a selector for hidden parameters, which are not accessible via I2C?

    Can you confirm one of these assumptions?

    Thanks and best regards,
    Johannes
  • 0 in reply to Johannes Brecher
    TI__Guru* 76230 points
    Hi Johannes,
    The bq27421 is a rom based gauge. There are only 3 specific chem ids which is supposed to serve as a one-size -fits -all id for different cells. That is practically impossile hence the need for you to make sure that the default chem id hardcoded on the gauge will work with your cell.
    The chem id parameters can't be changed for this gauge. Chem id consists of OCV and Ra and Rb values. You only have access to the Ra values as those are updated as the gauge learns.

    If you use a flash based gauge like the bq27520 or the bq27542, you will be able to change the chem id to one that is a close match for your cell for increased SOC accuracy.

    hope this helps.
    thanks
    Onyx