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BQ40Z80: Difficulty completing the learning cycle

richard wilson
Intellectual 585 points
Part Number: BQ40Z80
Other Parts Discussed in Thread: BQ34Z100-G1

Hi ,

We have tried to complete the learning cycle multiple times and we keep failing. Could I ask you to look at the attached logs and see if you can point me in the right direction? The application is a 7S, 1P,GAS_GAUGING_GOLDENFILE_FW.gg.csv 9.5Ah lithium battery pack.

Thanks for your help in advance,

Richard4890-005_Charge_GoldenFile_Step_One.log4890-005_Discharge_GoldenFile_Step_Two.log4890-005_Charge_GoldenFile_Step_Three.log4890-005_Discharge_GoldenFile_Step_Four.log

  • 0
    TI__Guru 63146 points

    I'll forward this to the applications engineer who supports this product and he'll answer on Monday.

  • 0 in reply to richard wilson
    TI__Guru** 105800 points

    Hello Richard,

    Just to clarify the BQ40Z80 does not support 7S applications any longer, it is for 2s-6s as stated in the datasheet. It is recommended to use BQ34Z100-G1 with a monitor in order to manage the BMS for 7s and higher cell counts with gauging.

    From reviewing your logs it looks like you may not be getting a big enough difference between your 2 DOD0 points, you need to get at least 90% change in DOD in order to update the Qmax for learning. DOD0 is based on 0 to 2^14 scale, so as long as between the 2 points there is at least 14,746 then it should qualify.

    Sincerely,

    Wyatt Keller

  • 0 in reply to Wyatt Keller
    Intellectual 585 points

    Hi Wyatt,

     We designed the board when the chip supported 7s, previously you told me that there has been no change to the silicon - so we should be okay with 7s ? for future boards we will redesign.

    I'll look at the DOD difference, I assume you mean the difference between fully charged and fully discharged should be 90% of QMAX?

    Thanks

    Richard

  • 0 in reply to richard wilson
    TI__Guru** 105800 points

    Hello Richard,

    There is no silicon changes, this does not mean there are no issues associated with 7S designs. Currently some applications will see some unexpected watchdog issues with 7S designs, and with inductive loads BQ40Z80 should not be used for 7S design since the higher voltage can get coupled into some of the sensitive pins and cause the part to become damaged when the voltage from the transient is above the absolute maximum rating. These are a case-by-case scenario and not every application will see these issues.

    Yes between the two relaxation points, the 90% is based on the chem ID OCV to DOD scale as I described above. It should be close to 90% passed charge of the maximum capacity of the cell (Qmax is not yet learned by the gauge, so it cannot be used as reference yet).

    Sincerely,

    Wyatt Keller

  • 0 in reply to Wyatt Keller
    Intellectual 585 points

    Thanks for the reply Wyatt,  so the only thing that I think we may be doing wrong is that we used a chem id that was close but not exact to our cell. The tool reported that it was 5% out, so we thought that was close enough for our purposes. Is this enough of an error so that the DOD measurement range is insufficient? My second question to you is if we sent you a cell for measurement, what sort of timescale would we be looking at for a turnaround?

    Thanks 

    Richard

  • 0 in reply to richard wilson
    TI__Guru** 105800 points

    Hello Richard,

    5% should be small enough to get the 90% change in DOD, learning should always be on the full voltage range of the battery, after learning the voltage range can be reduced if desired. We usually aim for 3% or less for best results. It would take apreoximately 6 weeks once we receive the cells for completion.

    Sincerely,

    Wyatt Keller