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Original question:

BQ27320: Settings Gauge

BQ27320: Design Capacity

G Cant
Intellectual 315 points
Part Number: BQ27320

Hello,

I am using a 3350mAh Battery with the BQ27320. This battery can go as low as 2.7V, but my device only works if the minimum battery voltage is 3.3V. 

If I discharge my battery from 4.2V (FULL) to 3.3V, the used capacity is 2500mAh.

My problem is: which value should I use for Design Capacity Setting in the Gauge, 3350 or 2500? If I don't use 2500mAh the State of Health register might be inaccurate.

Thank you for your help.

  • 0
    TI__Guru 57747 points

    Hello Guillermo,

    It would depend on what outcome is desired. Since the battery never discharges to the knee point(7%) the gauging accuracy is going to suffer in such an application.

    Since terminate voltage is set to 3.3V, the gauge will take that as the fully discharged point. From a state of health perspective adjusting the design capacity makes sense.

    The capacity of the battery would still be 3350mAh but you will not be using the full capacity. One way is to set reserve capacity parameter in data memory to account for the unused capacity.

    I would suggest trying both options and see which one gives higher accuracy.

    SOH is calculated slightly differently in both options because Design capacity is different.