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BQ27541-V200 Disable SOH?

Christopher Daily1
Intellectual 400 points
Other Parts Discussed in Thread: BQ27541-V200

E2E Team,

I have a customer using the BQ27541-V200 in an application where the shutoff voltage in the application is higher than the programmed termination voltage, 3.4 V and 3.0 V, respectively.  Because the application never sees the termination voltage, would this affect the accuracy of the SOC and SOH measurements? Also, is there a way to disable the SOH altogether? 

Thanks!

  • 0
    TI__Expert 3385 points

    Hi Christopher,

    SOC is determined using Qmax and remaining capacity of the battery, so just because the programmed termination voltage is higher than the actual termination voltage, the reported SOC should not be affected. What is likely to happen instead, is that your application will shut off upon falling below 3.4V, and the gauge will continue to read back remaining SOC even though the application is shut off.

    You can edit the programmed termination voltage easily using BQ Studio. First go to the "Data Memory" tab, and in that you will see a button called "Gas Gauging." Here you can reprogram the termination voltage to match the actual application EDV.

    Is there a particular reason why you would like to disable the SOH feature?

    Best,

    Justin

  • 0 in reply to Justin Erfan
    Intellectual 400 points
    Justin,

    My customer made a physical hardware error and it is affecting the SOH. As a workaround, the customer read to "set Q Invalid MinT to a value > Q Invalid MaxT. This should do it." That way they could continue to use the boards in the field and the remaining ones shipping. Unfortunately they could not locate anywhere in the configuration that shows those two parameters. He mentioned he found an app note but it states that they are protected and only TI can unlock them for adjustment.

    Also, in the configuration settings, there are quite a few parameters that are set to default values (Tapper current, Tapper voltage, etc). Ultimately, what configuration register settings play a roll in the SOH or SOC calculations?

    Thanks, this would be significantly helpful.
  • 0 in reply to Christopher Daily1
    Intellectual 400 points
    Justin,

    Any feedback on this yet?

    Thanks.
  • 0 in reply to Christopher Daily1
    TI__Expert 3385 points
    Hi Christopher

    All the parameters in the gauge have some effect on SOC and SOH, whether it's direct or indirect. For example, SOH is a function of FCC and design capacity, so the user must make sure he enters the correct values for these parameters based on the battery manufacturer's specs. Regarding SOC, SOC is a function of the passed charge between charging/discharging that the gauge updates during operation, and QMAX. It is imperative that the gauge has an accurate QMAX value (obtained initially on the learning cycle) for SOC to be calculated correctly. The battery needs to be properly charged at the manufacturer's specs in order to ensure a proper QMAX measurement. If the taper current and taper voltage are set too high or too low (depending on the manufacturer's specs), the battery may be overcharged or undercharged and will provide an incorrect QMAX, which affects SOC.

    Best,
    Justin