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BQ78350-R1: What is the Capacity Gain? How to set Current Gain without current calibration?

Mehmet Mutlu
Prodigy 100 points
Part Number: BQ78350-R1
Other Parts Discussed in Thread: BQSTUDIO, EV2400

Hello, I have a couple of questions related to current calibration.

1. What is the Capacity Gain? The technical reference manual explains what its value should be. But, there is no mention on how it is used. It seems like an irrelevant/unused parameter that stays in the manual as noise. The reference manual section "12.2.5.2 CC Gain/Capacity Gain Calibration" explains that the Capacity Gain = CC Gain  x 298261.6178. However, When I do the current calibration using bqStudio, the Capacity gain is set to the same value as the CC Gain (which is the value of the shunt resistor in units of mOhm, not unitless ADC reading as explained in the reference manual). bqStudio and the reference manual contradicts. Which one should I believe? Maybe I am missing something.

2. Is there a way to set CC Gain directly on the bqStudio (+EV2400)? When I directly try to set it to any value less than 1 mOhm, the CC Gain value does not change. It stays as 1 (default value). Only after a current calibration, it is set properly. Are we supposed to do current calibration for every battery we produce? I was expecting that there should be a way to set CC Gain directly with the "golden file" (*.gg.csv) using bqStudio. Most of the parameters are set correctly using the (*.gg.csv) file, but CC Gain needs manual current calibration.

Best

  • 0
    TI__Guru 54715 points

    Hi Mehmet,

    1. I will defer to an expert who should be back in the office next week.  Please look for a reply by 1/10.

    2. Generally yes, you can write CC Gain with your system or BQStudio.  BQStudio will impose a range limit which seems to be larger than that shown in the technical reference manual 12.2.27 and table 19-1.  For example I can write 0.94 but not 0.93, both of which are below the 1 mOhm shown as minimum.  Again I will defer to the expert.

     

  • 0
    TI__Guru* 81034 points

    Hi Mehmet,

    BQStudio displays both CC Gain and Capacity gain in terms of the sense resistor, however that is not how these values are represented internally.

    CC Gain (mOhms) = 8.4391 / x   where x is the value in the CC Gain flash. The default value in this register is 0x84070275 which represents 8.4381 in Xemics floating point. 

    Capacity Gain (mOhms) = (298261.6178 * CC Gain) / x  where x is the value in the Capacity Gain flash. This is also in Xemics floating point.

    Best regards,

    Matt

  • 0 in reply to Matt Sunna
    Prodigy 100 points

    Hi Matt,

    Thanks for the clarification. I got registers now. So it is just a visual representation difference with the chip and bqStudio. 

    It is still not clear for me how to set CC Gain without calibration (from a config file, ie. golden file and using bqStudio) for shunt resistors smaller than 1 mOhm (for example 0.5 mOhm or 0.25 mOhm). It seems like bqStudio is not allowing shunt resistors lower than certain value (above reply mentions a threshold around 0.93 mOhm) even though *.gg.csv file has the correct correct value.

    Best

    Mehmet

  • 0 in reply to Mehmet Mutlu
    TI__Guru* 81034 points

    Hi Mehmet,

    BQStudio does not import the calibration values by default (in case they need to be preserved). You can change this by selecting 'Import from File (Advanced)' and checking the box next to Calibration in the configuration.

    Best regards,

    Matt