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BQ20Z95: FCC high when charging at less than 4.2V per cell

Jeffrey Chase
Intellectual 520 points
Part Number: BQ20Z95


We have a configuration in which we are trying to charge a battery with a charging voltage of 4.05V per cell instead of 4.2V per cell on Li-Ion cells. The rom file was developed using the Chem ID for the cell. When the battery is cycled, FCC for the battery is high for what would be expected. The cells in question are 2.6Ah cells, but the application is trying to limit the power output to what would be equivalent to using 2.2Ah cells. 

After the first cycle in the cusomter's equipment, they are stating that the FCC is reverting to what would be expected, but the end user's are concerned about the initial high FCC.

Testing here, however, does not bear that out. It appears that FCC is always higher than what is desired and expected with the low voltage charge. 

Is charging at a lower voltage a viable option, and will the gas gauge actually be able to properly calculate FCC based on the low voltage charge limit?

  • 0
    TI__Guru 57697 points

    Hello Jeffrey,

    The gauge can properly calculate FCC even when a lower charging voltage is used. The termination conditions will need to be set to match. Did the first cycle include both a charge and a discharge?

  • 0 in reply to Shirish
    Intellectual 520 points

    Yes. Our test cycle fully charges the battery, then it fully discharges the battery, then it charges the battery back to 30% SOC. I'm pretty sure the termination conditions are correct. I am in the process of cycling one while capturing SMBUS and Flash data and will submit that once it is complete. I have to say, however, that I have had trouble uploading files to the forum lately. Not sure what I am doing wrong, but when I try to use the Insert Image/Video/File function at the bottom of the post, it always says The File or URL is not allowed to be uploaded.