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BQ24297: BQ24297 support lower charging currents

Jason Haedt
Expert 4600 points
Part Number: BQ24297
Other Parts Discussed in Thread: BQ25601

Hello,

The question has come up about how to support small LiPoly batteries with this chip.  The issue seems to be limiting the amount of charge current to a safe level for a small LiPoly.  For example a 380mAh battery, may only support a max charge current of 190mA.  For this device, it looks like the minimums bottom out at around 512mA.  At least that is the impression that I get from the datasheet.

Are there any techniques for limiting the charge current around 190mA? Probably the wrong part for the job but we have this charger built up at this point in time.

 Thanks,

Jason 

  • 0
    TI__Mastermind 25800 points
    Hey Jason,

    There are two options to limit the charging current on this device.

    1) If you are only charging the battery, and not planning on using a SYS load and charge together, you may use the input current limit along with a rough estimation of output power based on efficiency to limit the current delivered from the VBUS input source to the battery. Again, this option falls apart if you find that you are trying to drive your system (powered from SYS) while also trying to charge the battery.

    2) This is likely the best option. Our charger has a 20% mode, which sets the charge current to 20% of the ICHG setting programmed in register. Using REG02[0] = 1, the charger will drop the charge current to 20% of the setting and the precharge current to 50% of the setting. Therefore, if you set the ICHG current = 960mA, or REG02[7:2} = 6'b000111, and the FORCE_20PCT bit, you can get roughly 190mA of charging current. Please note that this mode does yield lower accuracy in terms of current regulation.

    There is a third option:

    3) Use the bq25601. This part was designed to be P2P compatible with the bq2429x family. From a board design perspective, you would only need remove a few components. One key difference is the lack of D+/D- support on that part. If you were utilizing D+/D- detection from the bq24297, then it may not be good alternative solution.


    Regards,
    Joel H
  • 0 in reply to Joel Hernandez II
    TI__Expert 4600 points
    Thanks Joel for the prompt feedback. We are going to look a the option 2 you suggest.