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BQ24115: Using BQ24115 with 4 x NiMH cells

Bruno Saraiva
Guru 13040 points
Part Number: BQ24115
Other Parts Discussed in Thread: BQ24702, LM317

Fellow engineers,

I would first append to the following thread: https://e2e.ti.com/support/power_management/battery_management/f/179/t/518127  but things get probably more organized if we move to a more "specific" question.

I need to start a charger design for 4 x NiMH, and was considering bq24115. It appears that NiMH ain't the cup of tea on most discussions here, so is this part a safe route to take for such chemistry? Our system does have a MCU available and attached to the charger, and we can implement some "failsafe" features to try and allow charging only under given conditions.

The charging voltage suggested by the original poster there seemed a bit low for 3 cells (4.4V / 3 = only 1.47v/cell, I would expect ~1.55 to be more like it, but since NiMH are not exactly constant voltage, I might be totally off here).

This product is not a battery charger, it is a system with "the bonus of allowing user to charge his batteries" - so we are targeting something simple, not consuming too much real state. I guess the question is whether bq24115 is a good option for 4xNiMH, or if not, are there suggestions for an alternative?

Thanks

Bruno

  • 0
    TI__Mastermind 25546 points
    hi Bruno,

    you might consider using a Li-Ion charger w/ adjustable output, in according with www.ti.com/.../slyt468.pdf
    in this way the range of options gets larger and you can consider the bq24702, for istance

    PS: since you have a uC you can make it also simple and cheap using any standard regulator in CC mode, like the LM317 or any LED driver actually...

    KR
    Vincenzo
  • 0 in reply to Vincenzo Pizzolante
    Guru 13040 points

    Greetings Vincenzo,

    Thank you for the comments. We have a couple more applications where MCU's and battery charging are involved, including a truck backup battery (nominal 24V).

    We will study you suggestion and try to create some evaluating circuits - hopefully adopt that CC regulator solution in the future. The particularly low volume on these applications and the fact that the products are not specifically chargers are key factors here.

    Thanks again for the input!

    Regards

    Bruno