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BQ27742-G1: Impedance algorithm updating

JDJ
Expert 3171 points
Part Number: BQ27742-G1

Hello,

My customer is planning on using the BQ27742-G1 and had a few questions.

  1. Will the gauge lose accuracy over time?
    1. As the battery degrades will the gauge be less accurate? 
    2. Does the device need to update and relearn every so often or is the algorithm constantly updating? 
      1. Are there any commands that need to be sent to relearn/update?
  2. Do the learning cycles need 100% discharge to complete?
    1. What is the min amount of discharge to ensure highest accuracy?
  3. If we want to limit users to 80% battery life, then will our fuel gauge be less accurate?
    1. Ideally, we will want to use 80% of battery life at the beginning then allow the users to use 100% of the battery life after years of use. 

Thanks!

  • 0
    TI__Genius 11750 points

    Hello Jack,

    This gauge uses our impedance track algorithm, you can find a helpful document here that explains a bit of how it works in this family of gauges.  As for the questions:

    1. The gauge should learn the batteries resistance and Qmax degradation as it ages, and ideally, won't lose accuracy over time. Certain conditions need to be met for this learning to occur, so it can be more difficult in certain applications. For example, you will need to relax occasionally for OCV measurements and discharge at a certain rate for impedance. The TRM will have more specific details about the conditions. This should all be automatic for the most part, you won't need to send any commands.

    2. You only need 1 full learning cycle on 1 gauge, which should be as close to 100% as possible. From there, it doesn't need to be 100% for updates. You can read the conditions in the TRM, but Qmax updates will require OCV measurements taken outside of the "flat region" which depends on chemistry. As for resistance updates, it mostly depends on rate and not SOC.

    3. It is possible to do that. As long as the 80% range can allow for OCV measurements outside of the flat region, which depends on chemistry. You would need a host MCU to change a few settings after the time passes. The downside is that changing these settings would require the gauge to be unsealed which may people would not want to do in the field. 

    Let me know if you have more questions.

    thanks,

    Alex M.