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BQ35100: Load requirements for accurate ACC or SOH Mode

user4867287
Intellectual 435 points
Part Number: BQ35100

Hi,

Are there any load behaviour requirements to get accurate ACC or SOH values?

I am thinking of "initial measurements" during "Startup Phase":
Is it ok if the battery is loaded during Startup Phase?
Is it ok if the battery load differs during a Startup Phase?
Is it ok if the battery load differs between different Startup Phases?
Must the battery be in any specific condition (5 hours relaxed, not loaded, etc) when the Startup Phase begins (GE set high)?

I also consider "Update Discharge/Voltage" during Active Phase":
Must the load be constant during an Active Phase?
How will short load pulses (0.5A / 1ms) affect ACC and SOH? 

Regards
CHA

  • 0
    TI__Mastermind 42535 points

    Hi,

    The gauge will not begin gauging until GE is set. So, no, the load will not be estimated. The load doesn't need to be constant in active mode, in accumulator mode the gauge uses an integrating coulomb counter so it will count pulses but we don't have data for 1ms pulses. In SOH mode, you are measuring the delta in resistance, so unless it hits a knee in the curve, you will get a fairly accurate SOH estimate.

  • 0 in reply to Batt
    Intellectual 435 points

    Hi,

    TI wrote: "...we don't have data for 1ms pulses". What du you mean?
    Will the 1ms /0.5A load pulse be included in the integration, or do you have any kind of function that skip short pulses?

    TI wrote: "In SOH mode, you are measuring the delta in resistance,...". Do the BQ35100 actually measure (or perhaps calculate) resistance in SOH mode?
    From what I can see in the data sheet, resistance is used only in EOS mode. Have I missed something?

    My original questions are raised due suspicions that load variations (directly after GE is set) might corrupt the OCV used in SOH mode, for calculating SOH = DOD(TermV) - DOD(OCV, temperature).
    Do the BQ35100 requires any specific load behaviour during the measurement of OCV (no load, constant load, load does not matter…)?

    Regards,
    CHA

  • 0 in reply to user4867287
    TI__Genius 10370 points

    Cha,

    SOH mode does rely only on the voltage measurement when the GE pin is asserted high. At GE high it will read Voltage and temperature to establish an SOH value. GE should be asserted when the battery is as close of OCV as possible, with as minimal load as possible. 

    Thanks,

    Eric Vos

  • 0 in reply to Vos
    Intellectual 435 points

    Hi

    Thanks Eric,

    SOH MODE

    From what I can see in the Operational Flow Diagram (Data Sheet, DS, page 16), battery voltage is also updated during the Active Phase. Is this update an additional measurement, or is it the OCV measured during the Startup Phase?

    ACC MODE

    With ref to my earlier question, above. Will also very short current pulses (0.5A / 1ms) be integrated and included in the number of counted coulumbs?

    Regards
    CHA

     

  • 0 in reply to user4867287
    TI__Genius 10370 points

    CHA,

    SOH_MODE: The only critical voltage is the one being taken at startup phase. This is the one used to determine SOH. Voltage measurements during active phase would only be used for the BAT_LOW warnings (if enabled) 

    ACC_MODE: There is an active sampling period, at 1mSec it is possible the current would be missed if not sampled appropriately. If there are many of these within a single active window. The gauge should be able to capture the charge expelled. The best way to know would be to run our EVM in this mode with the true load profile and see if it is captured.

    Thanks,

    Eric Vos

  • 0 in reply to Vos
    Intellectual 435 points

    Hi,

    My questions related to SOH Mode are now completely answered, thanks.

    But I have a remaining issue with the ACC Mode.
    For how long period is the current NOT sampled, and what value do the BQ35100 apply for integration during that period?

    As suggested I could do tests with my EVM, but one problem is that I have no control over the load profile. I do know the current peak value, but pulse lengths and PRF will vary very much (without my control).
    It might also be questioned how representative any results from one individual EVM are for an 1k batch of BQ35100.

    Best Regards
    CHA

  • 0 in reply to user4867287
    TI__Genius 10370 points

    CHA,

    I misspoke earlier swapping current for voltage. In ACC mode the coulomb counter runs continuously and updated every 1 second so you get a full one second conversion. 

    Voltage is samples 10 times over a second at an 8mSec window. 

    No charge will be missed

    Thanks,

    Eric Vos