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BQ2002: Selecting a suitable IC to charge 2 NiMh AA batteries from an USB micro cable

Paul Wang82
Prodigy 110 points
Part Number: BQ2002
Other Parts Discussed in Thread: BQ24105, BQ25071

Hello.

I want to build a charger to charge 2 NiMh AA batteries (in series) from an USB micro cable. The USB micro cable is commonly used to charge Android phones and is widely available. It outputs 5V, and current can range from 1A to 2A roughly.

I would like the charger to be safe, simple to design for, and has features to tell how many charge is in the battery (perhaps through LEDs).

Ideally, the LEDs can serve as a battery level indicator even when the battery is not being charged, but this may be something I have to implement separately. 

I also want the charger to be able to take into account of situations when the battery has a load while charging. (or is this I have to implement on my own?)

So far, I am investigating the BQ2002 chip. I wonder if the BQ2002 is one of the best chip for my application, or are there better choices?

Please advise. I'm still in the learning phase, but I do want to eventually commercialize this. Any comments or suggestions would be appreciated. 

Thanks

  • 0
    TI__Guru 56650 points
    2 NiMh AA batteries (in series) may not need 1 or 2A charging current. Specially, the bq2002 is a linear charger.

    When the battery has a load while charging and put the load on the battery, it is not good for charger to do the termination (sense the battery is fully charged). You may need to design a power path selector to put the load on the 5V input source directly when the input source is available and connect the battery to the load when the input source is not available.
    How quick do you want to charge the battery up? If you don't need to make a full charge in a short time and system load is not heavy, you may put the system load on the battery directly. Please check bq24105 and bq25071.
  • 0 in reply to Wang5577
    Prodigy 110 points
    Hi, thanks for the reply.

    But according to product data sheets, bq24105 and bq25071 are for Lithium based chemistry batteries.?

    I'm fine with designing a power path selector so that no load is put on the battery while being charged. I think bq2002 would be a suitable and simple IC to use for charging NiMh batteries? Just want to confirm. If you have any additional info that can be of help, that'll be great.

    Thanks
  • 0 in reply to Paul Wang82
    TI__Guru 56650 points
    If charging current has small C rate, we can use timer to terminate the charging. In such case, we can use bq24105.
    bq2002 is a suitable and simple IC for charging NiMH batteries.
  • 0 in reply to Wang5577
    Prodigy 110 points
    The user manual for BQ2002 provides very little diagram or direction on how to actually design an application. Are there more helpful resources? Preferably, there is an example application circuit I can use or emulate.

    Thanks