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Original question:

BQ35100: Query on measuring 30uA using accumulator mode

BQ35100: BQ35100's accuracy in ACC mode and EOS mode

user5874521
Intellectual 450 points
Part Number: BQ35100

Hi,

 https://e2e.ti.com/support/power-management/f/196/t/837077 In this URL, TI engineer said, the measured current need at least 10mA. 

What is the typical accuracy of BQ35100's charge accumulation when it is in ACC mode or EOS mode? What is the accuracy of charge accumulation when the current is >=10mA or <10mA?

For accurate measurement, the min current is about 10mA and what is the max current? 

  • 0
    TI__Genius 10370 points

    Current applied is all relative to the size of your senseR. The larger the senseR the bigger the current you could capture. However the gauge reports current in mA so to see it you would need to scale the value up.

    To do this you would apply 30uA, but tell the gauge you are applying say 30mA (scale by 1000). Then everything you do internal to the gauge would be referenced to this scale factor.

    Thanks,

    Eric Vos

  • 0 in reply to Vos
    Intellectual 450 points

    Hi Eric,

    Thank you for your reply!

    VsenseR is from –0.125 V to 0.125 V.  I choose senseR=0,1Ω, the same as BQ35100_EVM demo board.

    In our product, the Peak load current is about 600mA. And the load current is down to 20uA when the whole system is in sleep mode. In most of time, the current maybe 5mA, 10mA or 47mA.

    We will only use ACC mode in our product. I can't find the accuracy of BQ35100 in the spec. So what is BQ35100's accuracy in ACC mode, when the current is 600mA, 47mA, 10mA, 5mA and

    20uA? Do TI have a typical value about the charge accumulation accuracy?

  • 0 in reply to user5874521
    TI__Genius 10370 points

    This is not something i can spec because it depends on external components. I can provide hardware accuracy which can be found below. I would suggest you run a test after your calibration routing where you apply these specific currents for 1Hour and verify the charge accumulated. 

  • 0 in reply to Vos
    Intellectual 450 points

    Hi Eric,

    When calibrating 1A, we "Connect a 1-A load from BAT+ to PACK–." But the spec hasn't said how to connect when doing cc offset and board offset calibration.


    When doing cc offset and board offset calibration. We should confirm the current flow to Rsense is 0A.

    As we known, the current consume of BQ35100 will flow pass Rsensor, which make the current is not 0A.

    Can I connect the battery's + to BAT+ and battery's - to Pack-(the GND of BQ35100) like the second picture?  By reading the schematic of BQ35100_EVM(the third picture). I think in this condition, the current flow pass the Rsense will be 0A. Is it right?

  • 0 in reply to user5874521
    TI__Mastermind 24870 points

    Hello,

    This is a low side sense resistor. As long as you have current flowing through the sense resistor between Pack- and Bat -, that is fine. BAT+ and PACK+ in this case is the same bus.

  • 0 in reply to Kang Kang
    TI__Genius 10370 points

    Depending on the size of the senseR this might be an issue. I do not think it will be one in the grand scheme. What you could do it apply a hard short directly across the SRN/SRP pins to force the gauge to think there is 0 current. 

    Thanks,

    Eric Vos