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BQ34Z100-G1: Current/Average Current Sample Rate

Matt Adams
Prodigy 145 points
Part Number: BQ34Z100-G1
Other Parts Discussed in Thread: BQ40Z80, BQ40Z50, BQ28Z610

Hi,

Please could you provide some more information on the 'Current' and 'AverageCurrent' calculations used by the BQ34Z100-G1. I understand both these fields are updated every 1 second, but how are the values reported derived by the BQ?

Is ‘Current’ an instantaneous current reading or is it for example the average current seen over the 1 second period?

Is ‘Average Current’ a moving average over for example a 30 second period? ‘Average Current’ certainly seems to take a long time to update when a battery is connected to a load.

Thanks

Matt

  • 0
    TI__Mastermind 42535 points

    Hi Matt,

    Current is the instantaneous value. Avg current is the 14s low pass filtered value. It will catch up to the current for a steady load after the filter reaches steady state.

  • 0 in reply to Batt
    Prodigy 145 points

    Thank you very much for your reply, just a few more questions so I can fully understand:

    ‘Current’:

    The technical reference states this:

    “This read-only command pair returns a signed integer value that is the current flow through the sense resistor. It is updated every 1 s with units of 1 mA; however, if PackConfiguration [SCALED] is set, then the units have been scaled through the calibration process. The actual scale is not set in the device and SCALED is just an indicator flag.”

    So when you state this is an instantaneous reading, are you saying the BQ samples the current every 1 second and the value stored in this register is the current flowing through the sense resistor at that exact instance the BQ happened to sample? If so, does this mean if there is a high current pulse of 10A for a duration of 100ms within this 1 second sample period, there is only a 10% chance of detecting and recording 10A to this register, and a 90% chance of recording the base current in this register?

    Also how does this impact fuel gauging? If the short duration current pulses are missed by the current measurements sample rate of 1s, does this mean the fuel gauge wont know that the battery has been discharged as much as it actually has been in reality? Or does the BQ use average current through the low pass filter for its SOC% calculation?

    Many thanks for your help.

    Matt

  • 0 in reply to Matt Adams
    TI__Mastermind 42535 points

    Hi Matt,

    Yes, just by the nature of the coulomb counter not being on for data acquisition, you will miss counting current. One solution to this is, if you have a stack that's 2s you can try the bq28z610 or if 4s, the bq40z50, or if 6s to 7s, the bq40z80.

    This will certainly affect gauging because the coulomb counted current is going to be different from the actual current. However, since IT also implements an OCV lookup, this error can be mitigated to a certain extent.

  • 0 in reply to Batt
    Prodigy 145 points

    Hi,

    Thank you for your help, thank you for clarifying.

    Matt