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BQ40Z80: Pulsed Load SOC Tracking Accuracy

Seth Johnson
Intellectual 380 points
Part Number: BQ40Z80

My application will draw pulsed current loads up to 10A for tens of milliseconds at a time. From the datasheet I see "In NORMAL mode, the bq40z80 performs measurements, calculations, protection decisions, and data updates in 250-ms intervals." Will this part be able to accurately track the battery state of charge? Thanks.

  • 0
    TI__Mastermind 42060 points

    Hello Seth,

    We will look into this and give a response soon.

    Best Regards,

    Luis Hernandez Salomon

  • 0 in reply to Luis H. S.
    TI__Mastermind 42060 points

    Hello Seth,

    In the BQ40Z80 the coulomb counter, used to accurately keep track of the SoC during charging/discharging(See Section 7.1 of TR), integrates current over a time period. This means that the SoC should not be affected by the short current pulses, as it is being measured during a time period.

    However, the voltage drop caused by the short pulses could be missed. Which shouldn't be an issue unless your application does not tolerate brief voltage drops due to the high load spike.

    Best Regards,

    Luis Hernandez Salomon

  • 0 in reply to Luis H. S.
    Intellectual 380 points

    Hi Luis,

    Thanks for the explanation. The only value I could find regarding the "time period" is the 250mS interval mentioned in the datasheet. Does this mean there is a brief period of measurement followed by a 250mS gap until the next measurement? If so, how long is the actual measurement period? If the pulse of current happens in this 250mS gap, I'm assuming the accuracy of the tracked SoC is gradually lost?

    These pulses are irregular; there may be a 10mS pulse and a 1 minute delay before the next pulse, for example.


    The application will tolerate the voltage drops associated with the high current spikes so there's no issue there.

  • 0 in reply to Seth Johnson
    TI__Mastermind 42060 points

    Hello Seth,

    I don't believe it would miss it regardless of the delay. It doesn't take a measurement every 250-ms, I believe it integrates during that time period. So for your application it should still accurately keep track of the SoC.

    Best Regards,

    Luis Hernandez Salomon

  • 0 in reply to Luis H. S.
    Intellectual 380 points

    Hi Luis,

    Thanks, that makes sense. How much time does it spend outside that 250mS period? Is it not integrating outside of that period? If it was constantly integrating then why mention the 250mS period in the datasheet? Or does it constantly measure, but only updates the result of the measurement every 250mS? The wording in the datasheet groups "measurements, calculations, protection decisions, and data updates" all together and doesn't specify which is being done when.

    Thanks.

  • 0 in reply to Seth Johnson
    TI__Mastermind 42060 points

    Hello Seth,

    Yes, it constantly measures and integrates during the 250-ms period and then updates the result every 250-ms.

    The integration for Coulomb Counting is done by an integrating 16-bit Delta-Sigma ADC which greatly over-samples the signal. So you won't have to worry about missing the pulses.

    This Application Report(Chapter 3) from another of our devices might be helpful to better understand the Coulomb Counting. The over-all principle of operation is the same with the bq40z80, although some of the details in it will be different.

    Best Regards,

    Luis Hernandez Salomon