• State
  • Locked Locked
  • Replies 3 replies
  • Subscribers 63 subscribers
  • Views 984 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

BQ27426: Issues when setting trace resistance

Nicolas Venturo
Intellectual 810 points
Part Number: BQ27426


Hello,

I am working on a design that uses the BQ27426 as a battery gauge. Because we have somewhat long wires between the 10000mAh battery and the board, which causes a large voltage drop on large (>3A) currents, I tried setting the Trace Resistance parameter in the IT Cfg subclass (offset 75) to 110mOhm, which is our series resistance. However, when doing a discharge test, I encountered some weird behavior: after the gauge was measuring a current of -3500mA and a State of Charge of around 50% (and dropping), the state of charge (and estimated remaining capacity) suddenly jumped to 99%, despite the battery voltage and current staying the same. The battery temperature is set by the host and fixed at 25 C, so that can't be it.

Is there anything I can do to fix this? Thanks

  • 0
    TI__Guru* 76230 points
    Hi Nicolas
    -The trace resistance parameter has a unit of 4mohms. So your 110mohm trace resistance would be ~28mohm.

    Then further
    -Scale your trace resistance by a factor of design capacity/default design capacity. OR
    -set your default design capacity to be equal to the design capacity of your battery then there would be no need for scaling.

    Then Run a learning cycle and see if you get your resistance table updating and see if the problem goes away

    thanks
    Onyx
  • 0 in reply to Onyx Ahiakwo
    Intellectual 810 points

    Hi Onyx,

    I didn't know about the Trace Resistance being in units of 4mohm since that is not specified in the TRM, I'l try that out.

    I am not sure what you mean about scaling those parameters, how would that look for a 3.85V 10000mAh battery with 120mohm resistance and a maximum output current of 4A? What would I gain by doing this scaling?

    Thanks

  • 0 in reply to Nicolas Venturo
    TI__Guru* 76230 points
    your trace resistance would be 120/4=30mohm.

    in data flash you can either program 30 for trace resistance and default design capacity to 10000 and design capacity to 10000

    OR trace resistance will be set to 30/(design capacity/default design capacity)

    Doing this scaling allows the algorithm to implement the trace resistance properly when doing it's calculations

    thanks
    Onyx