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BQ40Z50-R1: Battery with LFP cells

Chen Jia
Intellectual 675 points
Part Number: BQ40Z50-R1
Other Parts Discussed in Thread: BQ40Z50

To whom it may concern:

We are trying to use BQ40Z50-R1 on LFP (lithium iron phosphate battery). In the existing ChemID list, there are some LFP cells, so I assume the fuel gauge should be able to support this cell type. However, we tried to match our cell to the list, and the best match still had 6.72% DOD deviation. The result is attached.

So if we use this 400 ID, the fuel gauge won't update. Could you help to advise what we should do? Maybe send some cells to you for ChemID generation?

Also I have some questions about the LFP cells settings:

What should we use to terminate charging? Taper current dropped very fast for LFP cells, and the voltage would drop during taper phase.

I don't have much experience on LFP cells, so if you can share some design guideline, it will be very helpful and very much appreciated.

Thank you!

Chen

  • 0
    TI__Guru** 102465 points

    Hello Chen,

    Chem ID 400 is the best match, the gauge will update using this ID. The max DOD error for LFP cells is usually higher due to the flat voltage, this is not avoidable.

    Charge termination is same method as any other lithium cell.

    The BQ40Z50 has features to help support LFP cells, I would make sure you have them enabled. For LFP type chemistries I would try to avoid long relaxation periods in the middle of SOC range due to flat voltage.

    Sincerely,

    Wyatt Keller