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BQ25713: Usage with NiMH cells, as hinted at in your charger selection table then never mentioned again.

JulianHigginson
Prodigy 120 points
Part Number: BQ25713

hi there!

I would like to use the BQ25713 to manage a NiMH battery pack (6 cell, ideally!) 
your selection table shows this part as suitable for all sorts of chemistries including NiMH, but the datasheet seems to infer the only cells it will work with are Li-Ion. 

Looking at the basic battery voltage and current specs for the part this shouldn't be a problem, but as NiMH obviously has different requirement to Li-Ion, I would like to understand any issues around doing this and what is needed to make the system work..... but there seems to be no info in the datasheet and no application notes I can see to discuss it. 

failing this, I'll have to go with LTC4010.. at least I can see that will work... even though it's quite primitive and doesn't really have all the features I'd like. 

  • 0
    TI__Expert 3320 points

    Hello Julian:

    Typical operation of the BQ25713 is that it is in CC mode until the termination voltage that is set in the "MaxChargeVoltage" register. Once this voltage is reached, the device will enter CV mode at that voltage, which will taper off the current in an exponential decay. This is the typical charging profile for LiIon and similar chemistries. It is not the profile that is generally recommended for NiMH, which is usually CC till around 90% capacity and then trickle charge. Also, the default settings that are selected with the CELL_BATPRESZ pin of 1-4 result in settings that correspond to LiIon cells or similar. I.e. they will set a termination of 4.2V * Cell Number, which is an appropriate number for LiIon chemistries.

    This does not mean, however, that the device cannot be used for NiMH. It is possible to use the device with NiMH, but it requires an external microcontroller to drive the current and voltage registers manually to fine tune the termination behavior. 

    So I would say that the device is really optimized to be easiest to use with LiIon and similar chemistries, but it is possible to use it with NiMH with some manual control by uC to fine tune current and voltage. Basically you have to set proper voltage/current initialization values for your chemistry and then implement the termination profile via uC.

    Regards

    Shishuo

  • 0 in reply to Shishuo Zhao
    Prodigy 120 points

    Aaah, thanks for the clarification... Ideally I'd like the BMIC to be able to do its job while the micro is off, so I guess this is a no go, unless I want to do some work on power domains and some significant work to manually force charging behaviour..

    Thanks anyway, but it looks like the nearly 2 decades old LTC part will get to go in a new design...

    It's a real shame this project can't use Li-Ion batteries, like everything else I've designed to use rechargeable batteries in the last 10 years...