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BQ27426: Consult for register setting

Wang Dong
Intellectual 600 points
Part Number: BQ27426

Hello：

Our company is using BQ27426 to manage lithium batteries. There are some questions about the setting of Simulation ResRelax Time, User-Defined Rate-Current and User-Defined Rate-Power registers. What are the functions of these three registers? If not set, what is the default value? What is the basis for setting the default value? I look forward to your reply, thank you!

  • 0
    TI__Guru 62386 points

    ResRelaxTime controls how the gauge models transient behavior (how cell voltage changes from relax to discharge). The longer this number, the longer the gauge will take to let the predicted cell voltage approach OCV - I*R.

    User Defined Rate (Current and Power): Some applications don't lend themselves to one of the other prediction settings (Load Select), hence it may be necessary to specify a load that you want the gauge to use to predict capacity. It's possible to either specify a constant current or a constant power, depending on the prediction model (Load Mode).

    The default value for ResRelaxTime is chosen by TI to work with most cell chemistries. The User Defined Rates are 0 by default (they depend on the application).

  • 0 in reply to Dominik Hartl11
    Intellectual 600 points

    Thanks for you reply

    User Rate-mA：After configuring to fixed current mode (load mode=0 load select=6) and satisfying the dsg current threshold condition, is rm predicting according to the set fixed current, not caring about the current actual discharge current?

  • 0 in reply to Dominik Hartl11
    Intellectual 600 points

    Thanks for you reply

    What are the corresponding current sampling times for each of the three configurations in the figure below?

  • 0 in reply to Wang Dong
    TI__Guru 62386 points

    The gauge runs on a 1 second cycle and it calculates the averages once a second.

  • 0 in reply to Dominik Hartl11
    Intellectual 300 points

    1. Is this means that gauge read the current every seconds and set the value into AverageCurrent()?

    2. if we set load select=1, the current is used as the average current of AverageCurrent() for a discharge cycle?

    3. If we set load select=3, T=14s means the current is update every 14sec by the current from a low-passed-filetered version of AverageCurrent()? without average calculation?

  • 0 in reply to chengxiaobin
    TI__Guru 62386 points

    #1: Yes, the gauge measures current once a second (it integrates the measurement over the sense resistor over 1 second). Then it uses this measurement to calculate a moving average, AverageCurrent().

    #2: AverageCurrent() is a moving average but the average for capacity prediction is the average from the beginning of discharge. If you want to user AverageCurrent() for load prediction, you'd have to use Load Select = 2.

    #3: This means that the moving AverageCurrent() is low-pass filtered with a time constant of 14 seconds and this low pass filtered value is used for capacity prediction.