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BQ20Z95: Ra Table Transients?

Jeffrey Chase
Intellectual 520 points

Part Number: BQ20Z95

Previously I had started a thread regarding a sudden drop in FCC in a battery, then recovery of FCC after another full cycle. At the time, there was one battery that had been seen with the issue. Our customer now reports that they have found three more acting in a similar way. They were returned to the customer because their device had shut down due to the battery believing it had no more capacity. When they received the battery, FCC was low and values in the Ra tables were up to 3X normal.

Have there been any reports from the field from other manufacturers using this gas gauge for transient, recoverable changes in the Ra tables? Has TI done any testing to determine possible transients in the gas gauge firmware that could result in errors during cell impedance calculations?

  • 0
    TI__Mastermind 25955 points
    Hi Jeffrey,

    Linking your referenced post here: e2e.ti.com/.../614760

    I will follow-up tomorrow after a discussion with the systems engineer for this device.

    Sincerely,
    Bryan Kahler
  • 0 in reply to Bryan Kahler
    TI__Mastermind 25955 points
    Hi Jeffrey,

    I apologize for the delay in response - thank you for your patience with me getting back to you.

    Did this FCC drop occur during use in cold temperatures? Did the recovery occur in warm temperatures?

    Have the Ra tables been optimized for this Gauge? What about the Rb tables?

    Please try optimizing the Rb tables for the gauge for low temperature performance ( http://www.ti.com/tool/gpcrb ).

    Sincerely,
    Bryan Kahler
  • 0 in reply to Bryan Kahler
    Intellectual 520 points
    It doesn't appear that the use case for this battery entailed a low temperature discharge. The recovery did occur at room temperature.

    The Ra tables have been selected based on cell manufacturer and model using TI's bqEVSW tables. We are in the process of performing tests for the Ra tables, and batteries using the original tables and a new set of tables are being cycled.

    I have seen a reference to the Rb tables previously, but am not clear on where these are stored or how they are developed. Is there a white paper somewhere explaining these tables?

    The customer is now finding more of these in the systems that use the battery in question, as well as batteries that return a low FCC and are not able to recover the FCC to an appropriate level. I have recently received several of these batteries and will be pulling data from them.

    A third failure mode is a cell imbalance after only a few cycles. Could all of these be related to non-optimized Ra tables? We are pursuing other failure options, but any help you could provide would be greatly appreciated.