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BQ34Z110: How do you change data flash parameters to account for size of sense resistor

Mark Watson
Intellectual 530 points
Part Number: BQ34Z110
Other Parts Discussed in Thread: BQ34110, BQSTUDIO, BQ34Z100-G1

Hello,

I am using the BQ34110EVM with high capacity PbA batteries. I know how to scale the current/capacity, but I am not sure how to change data flash parameters to account for the size of a different sense resistor. I am bypassing the 0.01 Ohm resistor that comes on the EVM (to ensure the input voltage generated across the current-sense resistor does not exceed ±125 mV), but I can't figure out how to tell the BQ34110 that the sense resistor is a different size.

I think it has something to do with the factory calibration (chapter 5 of the bq34110 user manual), but I am not clear on the meaning of the CC Gain, CCDelta, and CC Offset parameters.

I found this thread: It appears all I have to do is apply a known current, use bqStudio to calibrate the current, and then CC Gain and CC Delta will be automatically updated to reflect the value of the new resistor: is this correct? What about when I scale the current because of my high capacity application: wouldn't this alter the data flash parameters for CC Gain and CC Delta and negate the previous actions?

Thanks.

Mark

  • 0
    TI__Intellectual 1735 points

    • Hi,
    • It is not recommended to bypass the 0.01 ohm resister since it works as a coulomb meter to calculate the energy go in or out the battery.

  • 0 in reply to answer
    Intellectual 530 points

    Terry,

    I appreciate your advice, but the coulomb counter pins have maximum voltage ratings of 125 mV. For higher current/capacity applications, the sense resistor must be sized appropriately. Are you saying customers can only ever use a 0.01 Ohm sense resistor with the bq34110? There are no other options for field applications? So you're saying every field application of the bq34110 requires a 0.01 Ohm sense resistor: I do not think TI would agree with this statement.

  • 0 in reply to Mark Watson
    TI__Guru 73830 points

    Mark

    You can use a smaller sense resistor. You will need to remove the one that is installed on the EVM. It is recommended that you place the new sense resistor on the PCB, but you can locate it off of the board. I recommend that you use a twisted pair wire to connect the sense resistor to the EVM.  The gauge can support up to 32A, so you will need to use current scaling, if you requirements exceed this. I have an applications note on the bq34z100-G1 product website that covers this process.

    Tom

  • 0 in reply to ThomasCosby
    Intellectual 530 points
    Hello Tom,

    Thank you. I have already done all of this. I am just looking for confirmation of the method I described in my original question for scaling.

    Thanks.
  • 0 in reply to Mark Watson
    TI__Guru 73830 points
    The CC Gain and CC Delta parameters do reflect the resistance or the scaled resistance, if used.