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NiMH battery pack using the BQ26220 monitor

mike rausch
Prodigy 60 points
Other Parts Discussed in Thread: BQ26220, BQ27010, BQ27000, BQ2013H, BQ2016, BQ2014H, BQ2060A

I am designing a NiMH battery pack (6 series connected cells) that requires a gas gauge / monitor. 

I was planning on using the BQ26220 monitor (HDQ and a GPIO are necessary).  Planning on using an op-amp, half-battery voltage supply (and sense) for the bq26220. 

Not much board space.  Design needs to be intrinsically safe (large components and considerable spacing).

Cell capacity is 2.7Ahr, Charge current will be 2A.  Discharge current is around 100mA with 500mA peaks. 

Is the bq26220 good choice?  acceptable choice?  bad idea? 

Is there a better choice? 

Thanks

mike r

  • 0
    TI__Genius 14985 points

    The bq26220 is our most recent standalone battery monitor (not battery gauge), but you might be better off using a bqJunior gauge and ignore the gauging functionality.

    See this SLUA347: Building a Superior Battery Monitor with the bq27x00

    Since you want HDQ you could go with the bq27000 (or bq27010) but since you are not using the gauging function then you don't care about the gauge improvements in the bq27010 so it's a wash.

    Since the bq27000 also has a CPU and RAM, it does consume a little more power than the bq26220, but it might be more widely available since it ships more volume.  There might even be some extra features it has that you might like.

  • 0 in reply to dMax
    Prodigy 60 points

    dMax

    Marketing would like a gas gauge.  I didn't find one specifically for NiMH so I was hoping that using a battery monitor and algorithms / look-up tables in the host process would be able to produce a gas gauge function.    Does this make sense or just another bad idea?    I suspect it will be a fair amount of work to get the algorithms correct.

    We are using the bq27010 in a Li+ version of the battery pack.   I was assuming the algorithms built into the 27010 were only for Li+ chemistry.   I guess we could still use the 27010 as a monitor only. 

    We won't need large quantities but we will need them at a moments notice...

    We will need to differentiate a NiMH battery pack from a Li+ pack via the HDQ port.   Any thoughts?

  • 0 in reply to mike rausch
    TI__Genius 14985 points

    We do actually have a few NiCd/NiMH gauges, although they are quite long in the tooth due to the popularity of Lithium.

    Try bq2013H, bq2014H, and bq2016.  They are all single-wire communication.

    We also have the bq2060A which offers multi-chemistry support.

  • 0 in reply to dMax
    Prodigy 60 points

    I looked at the bq2014H.  It doesn't have a GPIO pin.  I need to read the GPIO (as an input) to determine when the battery pack is in a charger. 

    The bq2013h seems very similar to the 2014.  The 2016 and the 2060 are both pretty big parts.    PCB is a two layer flex board.  Layout might be an issue. 

    That's what lead to the 26220.    

     Is it feasible to create a NiMH gas gauge with a battery monitor and a host processor?

  • 0 in reply to mike rausch
    TI__Genius 14985 points

    The more dynamic your temperature and load, the tougher it will be, but you can definitely do it. 

  • 0 in reply to dMax
    Prodigy 60 points

    I think we will go with the bq26220 or the bq27010 as a monitor.   Looks like the 27010 is cheaper than the 26220.

    We should be able to put some bogus data in the EEPROM of the NiMH pack that will differentiate it from the Li-ion pack if we use the 27010 for both packs. 

     

    Thanks for all your help. 

    mike r