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BQ27Z561-R2: Power management forum

L
Prodigy 230 points
Part Number: BQ27Z561-R2
Other Parts Discussed in Thread: BQ40Z50,

The original document is SLUA997, www.ti.com.cn/.../slua997.pdf

For the problem as shown in the figure below,

①The second picture, why DOD0 jumps when the discharge current increases, I don't understand it very well here. Did you trigger Fast OCV?

② Qmax does not have to be 37% to update? Why does it update after 20% discharge?

③Why is Qmax updated and DOD0 also updated?

④Qm and Qmax filter why I can't find the register in the TRM  ?

Also ask TI engineers to help answer questions, thank you!

  • 0
    TI__Guru** 106140 points

    Hello L,

    The fast OCV feature allows the gauge to take an OCV that is qualified for Qmax updates, it does not require a full discharge or 37% discharge like the traditional method of Qmax updates.

    This new feature models the RC time constants and estimates what the OCV will be in the future, so we only need a very short relaxation during discharge to get a good OCV measurement.

    Sincerely,

    Wyatt Keller

  • 0 in reply to Wyatt Keller
    Prodigy 230 points

    HI Wyatt Keller ,

    I'm glad to see your reply. I haven't communicated on foreign language forums for a long time, which is a great experience. I still have the following questions, please help to confirm.

    ① In the second picture, when the discharge current increases twice, DOD0 jumps. My current understanding is that the Fast OCV is triggered twice. I don't know if my understanding is wrong

    ②According to your prompt ( it does not require a full discharge or 37% discharge like the traditional method of Qmax updates.), my current understanding is that Qmax is updated by combining the accumulated power of the two DOD points updated by Fast OCV . I don't know if my understanding is wrong.

    ③Which product are the registers of Qm and Qmax filter on? I only found the following registers in BQ40z50 and BQ27Z561-R2

    • Qmax delta: 5% -> 2%

    • Qmax upper bound: 130% -> 105%

    But I didn't find Qm and Qmax filter.

    Still very grateful for the support you already have, Your answer is more professional than the answer of the Chinese forum, I'm sure I'll also enjoy being here to ask questions and learn from you in the future.

    Best Regards,

    L

  • 0
    Prodigy 230 points

    HI Wyatt Keller ,

    I'm glad to see your reply. I haven't communicated on foreign language forums for a long time, which is a great experience. I still have the following questions, please help to confirm.

    ① In the second picture, when the discharge current increases twice, DOD0 jumps. My current understanding is that the Fast OCV is triggered twice. I don't know if my understanding is wrong

    ②According to your prompt ( it does not require a full discharge or 37% discharge like the traditional method of Qmax updates.), my current understanding is that Qmax is updated by combining the accumulated power of the two DOD points updated by Fast OCV . I don't know if my understanding is wrong.

    ③Which product are the registers of Qm and Qmax filter on? I only found the following registers in BQ40z50 and BQ27Z561-R2

    • Qmax delta: 5% -> 2%

    • Qmax upper bound: 130% -> 105%

    But I didn't find Qm and Qmax filter.

    Still very grateful for the support you already have, Your answer is more professional than the answer of the Chinese forum, I'm sure I'll also enjoy being here to ask questions and learn from you in the future.

    Best Regards,

    L

  • 0 in reply to L
    TI__Guru** 106140 points

    Hello L,

    The gauge will only calculate the Fast OCV once, I'm not sure I understand the portion of the graph you are referencing.

    The Fast OCV still requires 2 OCV readings in order to find the two DOD values for calculating Qmax. It uses them in conjunction with the passed charge between them.

    Can you show an example of where you see the Qmax filter and Qm?

    Sincerely,

    Wyatt Keller

  • 0 in reply to Wyatt Keller
    Prodigy 230 points

    HI Wyatt Keller ,

    ①I guess that in the two positions of the red circle, Fast ocv happened twice, I don't know if my guess is correct

    ②The original document is SLUA997, www.ti.com.cn/.../slua997.pdf

    4 Fast OCV

     The following changes can be made to the Qmax filters to reduce the errors that can be introduced due to frequent Qmax updates without a deeply discharged cell.

    • Min%passed charge for Qm: 37% -> 10%

    • Qmax filter: 96% -> 24%. The relationship between min%passed charge for Qm and Qmax fillter is: qmax filter <256*min%passed charge for Qm. One must not be modified without the other.

    But I haven't found Qm and Qmax filter in TRM.

    Best Regards,

    L

  • 0
    Prodigy 230 points

    HI Wyatt Keller ,

    ①I guess that in the two positions of the red circle, Fast ocv happened twice, I don't know if my guess is correct

    ②The original document is SLUA997, www.ti.com.cn/.../slua997.pdf

    4 Fast OCV

     The following changes can be made to the Qmax filters to reduce the errors that can be introduced due to frequent Qmax updates without a deeply discharged cell.

    • Min%passed charge for Qm: 37% -> 10%

    • Qmax filter: 96% -> 24%. The relationship between min%passed charge for Qm and Qmax fillter is: qmax filter <256*min%passed charge for Qm. One must not be modified without the other.

    But I haven't found Qm and Qmax filter in TRM.

    Best Regards,

    L

  • +1 in reply to L
    TI__Guru** 106140 points

    Hello L,

    The Fast OCV only happens once when the gauge briefly stops discharging. The first one occurs due to the charge termination, this is mentioned in the documentation. When we update DOD at EOC it also updates DOD0.

    It appears these register are still private (Qm and Qmax Filter). Changing these are not needed unless you require there to be less than 37% change in DOD for a Qmax update. The defaults should work for most applications.

    Sincerely,

    Wyatt Keller

  • 0 in reply to Wyatt Keller
    Prodigy 230 points

    Thanks,Wyatt Keller~