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BQ34Z100-G1: FCC CHANGES

Gorka Lorea
Expert 1620 points
Part Number: BQ34Z100-G1

Hi,

I am using a BQ34z100-g1 with an 8s2p LiFePO4 batteries. The nominal capacity of the battery is 3200mAh.

I have obtained the golden image of the battery and load it in the bq34z100-g1 and now I am doing cycles to the system simulating the real application. 

I have logged the following parameters to understand better the IT algorithm: Voltage, current, SOC and FCC.

As you can see in the graphic the FCC changes many times (not big changes but one peak that raised almost 200mAh) when battery is at 100% SoC. Looking at the document when IT algorithm is explained I can read

However, none of these conditions (resistance grid-point, exit of relaxation or end of discharge) are fullfilled.

1. Why is FCC changing with so high frequency?

2. Is due to FCC simulations?

 

 

Best regards,

  • 0
    TI__Guru** 105770 points

    Hello,

    The FCC value calculated is based on the equation you linked, the gauge updates this value more often than each grid because many things determine FCC. Because there's only 15 Ra grid points the gauge runs simulations more often than 15 times per cycle based on the temperature change and voltage change.

    Let me know if you have any more questions!

    Sincerely,

    Wyatt Keller 

  • 0 in reply to Wyatt Keller
    Expert 1620 points

    Hi Wyatt,

    Thanks for your quick response. I have some questions about it:

    1. I would like to know the exact conditions under BQ34z100-g1 do Capacity Simulations. This is very important for us to understand the behaviour of the fuel gauge in our application.

    2. Why do you think changes in FCC are more visible when SoC is 100% (but FC is still not achived)?

    3. What do you think might be the reasons for the peak in FCC you can see in the 2nd graphic (almost 200mAh increase)?

     

    Best regards,

  • 0 in reply to Gorka Lorea
    TI__Guru** 105770 points

    Hello,

    There are many conditions that the gauge will run simulations, I don't believe this is in the documentation and may be confidential. The gauge will constantly be updating FCC when other parameters are changing. The gauge updates RAM with new values every 1 second, this is the minimum time interval between when simulations could be run.

    If there's still current flowing in the gauge when it reaches 100% SOC it will be trying to correct for this.

    I believe that may be erroneous measurement, either by the gauge or in the communication.

    Sincerely,

    Wyatt Keller