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Why would a calibrated bq2060 Battery Pack read so much temperature drift for *I*?

Michael Banak
Intellectual 915 points
Other Parts Discussed in Thread: BQ2040

The data below is very typical for a particular battery pack in my space. The pack is being pulled by a Constant Current Load, But it is reproducible elsewhere in our space. The E-Load (sitting at ambient) has ~5mA of offset of its own, which is accounted for in this narrative.

- Further, this parabolic trend (cenetered around room temp) appears at 3A as well.

- For rated 0 to 50C range of operation, this data shows about 5% of spalsh.

- At the high and low tempoeratures, there is a corresponding offset in the reading with 0 current pull. In other words, at 50C, there is about +50mA of current pull, evenb with no load on the battery.

- This, whatever is drifting here, it appears to be an offset term

What are the prime suspects for this phenomena?

 

I (-20C) = -927mA

I (0C) = -986mA

I (15C) = -1004mA

I (25C) = -1007mA

I (50C) = -949mA

Regards,

Michael A. Banak

  • 0
    TI__Intellectual 940 points

    Michael,

    The issue is drift of the ADC offset with temperature.  The gauge doesn't use the ADC to measure coulometrically, so this won't cause an error in computing the available capacity.  The VFC has a much lower offset that is also more stable, but measuring current with the VFC takes a long time and the slow response to current changes like previous bq2092 and bq2040 products was frustrating to the customer.  There is an FAQ covering this subject:  Why does the bq2060/bq2060A Current read non-zero with no current flowing?

    I expect your sense resistor is less than the typical 30mohms normally used with this gauge.  The Current accuracy after calibration specified in the data sheet is +/-1mV/Rs.  I would guess that your sense resistor is probably closer to 10mohms.

    Bill

  • 0 in reply to Bill J10799
    Intellectual 915 points

    Thank you Bill.

     

    I have a follow-up request, but first:

    - I am using a 20mOhm sense resistor.

    - It is a relief to know that the I-readings we see do not play into the faul-gauge coulomb-count.

    The link you kindly provided isn't working. May I ask you to reload on that? Maybe you could attach some version of it to your reply, if the WEB archive is gone. That report looks like just the ticket!

     

    - Michael

  • 0 in reply to Michael Banak
    TI__Intellectual 940 points

    Michael,

    Sorry about the bad link.  This one will get you to the analog knowledgebase:

    http://www-k.ext.ti.com/sc/technical-support/analog-kbase

    You can type in part or all of the previous link I sent and it will give you a list of relevant topics.  There are a number of topics in this knowledgebase that may be of interest to you.

    Bill