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BQ40Z50-R2: BQ40Z50-R2 Sample Rate

Zhihan Zhang
Expert 1100 points
Part Number: BQ40Z50-R2
Other Parts Discussed in Thread: BQ40Z50

Hi TI team,

I have couple questions about measurement for BQ40Z50-R2. For example, I have a pulse discharge with 15mA of 1s, 100mA of 0.1s, 150mA of 0.2s, and 200mA of 0.7s. The total period is 2s.

Will the IC be able to measure every peak of the discharge current per period for current measurement?

With such discharge rate, will the fuel gauge be able to account all peaks per period for capacity measurement? Or will the fuel gauge accuracy be decreased for such discharge?

Thanks in advance!

Best Regards,

Zhihan

  • 0
    TI__Guru 52115 points

    I have assigned your question to my colleague and we will get back to you.

    Andy

  • 0 in reply to Andy Liu (BMS)
    TI__Genius 10370 points

    Zhihan,

    Does this load profile repeat continuously? 

    The issue will be getting resistance updates if this is a pulse and rest for a long time. For resistance to update you need to be in discharge mode for an extended time.

    The gauge will capture all of the charge from this pulse, so your passed charge will be accurate. 

    thanks,

    Eric Vos

  • 0 in reply to Vos
    Expert 1100 points

    Hi Eric,

    Thank you for your help!

    Yes, the load will be repeated every 2s until fully discharged.

    So regardless the resistance, the fuel gauge will just account every peak right? The resistance here you mean the resistance of the cell right?

    Another question is what if I lower the dsg threshold to force to stay in discharge mode, what may be the good or bad impacts for the fuel gauge?

    Thanks again,

    Zhihan

  • 0 in reply to Zhihan Zhang
    TI__Guru 52115 points

    Your understanding is correct.

    The DSG Current Threshold should be set to a value lower than the minimum system draw when in active mode. A value below C/10 is generally reasonable. Also, the Quit Current is must be less than the Dsg Current Threshold.

    Andy

  • 0 in reply to Andy Liu (BMS)
    Expert 1100 points

    Thank you very much for you answer!

    So what if, in extreme case, I set quit current to a very low value or even 0mA, that means the fuel gauge probably never enter to relax mode. Will that help or there will be some downside of it?

    I see there's gap between quit current and discharge threshold or charge threshold. Just curious, what if the |Current()| is between quit current and discharge threshold or charge threshold, what's the status of the IC?

    Zhihan

  • 0 in reply to Zhihan Zhang
    TI__Guru 52115 points

    Hi Zhihan,

    See my comments below.

    So what if, in extreme case, I set quit current to a very low value or even 0mA, that means the fuel gauge probably never enter to relax mode. Will that help or there will be some downside of it?

    [Andy]  RELAX mode is very important for gauge.  Open circuit voltage (OCV) and QMax updates only take place in RELAX mode.  These two events are very critical for the gauge to perform properly. 

    I see there's gap between quit current and discharge threshold or charge threshold. Just curious, what if the |Current()| is between quit current and discharge threshold or charge threshold, what's the status of the IC?

    [Andy] The gauge should stay in the DISCHARGE or CHARGE mode.  See Section 6.3 of bq40z50 TRM for the details. 

    Andy