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BQ34Z100 design scale for 24V/100Ah battery

Lewis Conrad
Prodigy 170 points
Other Parts Discussed in Thread: BQ34Z100, BQSTUDIO

Hello!

I have read the datasheet and some posts in this forum regarding the scale in the BQ34Z100 and I'm still a little bit confused.

I need to use a 24V, 100Ah battery with 10A maximum charge/discharge current.

I realize that this IC only supports up to 29Ah, so there is the need to do some scaling.

I was thinking in using a scale of 4, so that 100Ah/4 = 25Ah (<29Ah). But this scaling would only be made by calibrating the current so that when a 8A current was going through the sense resistor, I would write on the bqStudio that it was 2A. This way, all current and derivative readings like power, energy, etc, would have to be multiplied by 4 by the MCU after read from the BQ34Z100 to show the real value. The SCALED bit from Pack Configuration registers can be set only as an indication for the MCU to know that the calibration had been scaled. Is that right?

Now, I'm confused by the "Design Energy Scale" register. Should this be used along with the calibration scaling described above or is it an alternative method that should be used without doing a calibration scaling?

What do you recommend for my particular application?

Thank you.

  • 0
    TI__Guru 73830 points
    You are correct that scaling is required for your application and the SCALED bit does not do anything. The Design Energy Scale will change the enery parameters from mW to cW to allow them to be stored in registers. You will still have to use scaling, because the capacity parameters will still exceed 29Ah. Scaling by 4x should be okay for your application.
  • 0 in reply to ThomasCosby
    Prodigy 170 points
    Due to Design energy limitations (32767mWh maximum) I must use x10 current calibration along with x10 "Design Energy Scale" so that 24V, 100Ah battery shows 24V * 100000mAh /10 /10 = 24000.
    I am thinking correctly?
  • 0 in reply to Lewis Conrad
    TI__Guru 73830 points

    Lewis,

    The df.fs file is different from the .dfi file referenced in the going to production document. The dfi is a binary image of the data flash, where the df.fs file is a text file containing the commands to write to the device. I will try to find a better document to help you. All of the parameters in the bq34z100 DF are based at a cell level, so the Design Energy will be the Design Capacity x the Design Voltage. The Design Voltage is typically 3.6V for a Li-Ion cell. So, if you Design Capacity is 25Ah (100Ah/4), and the Design Voltage is 3.6V, then the Design Energy = 25*3.6 = 90000mWh or 9000 cWh.

    TOm

    Tom