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BQ27421-G1: What is the initial accuracy of the SOC reported by the BQ27421-G1 Fuel Gauge

Part Number: BQ27421-G1
Other Parts Discussed in Thread: GPCCHEM,

Hi,

I'm using BQ27421-G1A fuel gauge in my design. 

I will connect battery with my board and configure the fuel gauge registers (Design Capacity, Design Energy, Termination Voltage and Taper Rate) through microcontroller over I2C. Now I want to know what will be the accuracy of the SOC reported by the fuel gauge in this case ?

Also what needs to be done to improve the accuracy of the SOC reported by the fuel gauge ?

Thanks & Regards

Vidyasagar

  • Hi Vidyasagar
    Before settling on using the bq27421, you need to determine if the device is ideal for your battery chemistry using our online tool called gpcchem. if the report comes back that the device is a good match, then after configuration, you need to cycle the cell so the gauge learns the resistance value and the qmax of the battery
    thank
    Onyx
  • Hi Onyx,

    Firstly we are using LiCoO2 Lithium Polymer battery, which is supported by BQ27421-G1. Then what is the requirement of gpcchem tool ?

    Secondly BQ27421-G1 quick start guide says that it doesn't require a learning cycle. Why are you saying opposite ?

    We selected this fuel gauge with the idea of using it immediately after programming 4 registers.

    Please clarify on the above issues.

    Let me know what is the initial accuracy of the SOC reported by the gauge after programming the 4 registers.

    Thanks

    Vidyasagar

  • hi Vidyasagar
    There are a thousand and one different flavours of LiCoO2 batteries with different capacities and different internal resistances. You can't have an ideal one size fits all chem id. For this reason you need gpcchem to determine if the bq27421 would work for you. It appears you are relatively new to using our gauges. you do not want to be too far into your design only to realize that you can't get the desired accuracy from the bq27421. Your error could be as large as 60 % or more or as little as 1%. It just depends on if your cell profile is close to the hard coded chem ids in the bq27421 flavors. That is what the gpc chem will tell you. if you are close enough then the device can learn on the field and you don't need additional cycling. For best performance it is always better to run at least a discharge cycle for better accuracy

    thanks
    onyx