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BQ24172: NiMH Battery charger

Electro_crazy
Intellectual 525 points
Part Number: BQ24172
Other Parts Discussed in Thread: BQ2000

Hello,

Can IC BQ24172 be used for NiMH Battery charging? because in the list of battery charger IC it is mentioned that cell chemistry of NiMH can be used but in the datasheet nothing about NiMH is mentioned.

If not, then is there any other IC with power path priority to USB power & NIMH battery as supplement?

Thanks in advance

  • 0
    TI__Guru**** 165766 points

    Hi Jain,

    If NiMH battery is to be charged at less than < 0.5C, then it is acceptable to terminate with only a timer, which can be set using the BQ24172's TCC pin.  If used like this, the BQ24172's VBATREG via the FB resistors should be used as a battery OVP instead of termination.  The concept is explained in more detail in app note at the link below:

    For fast charging NIMH at >0.5C, termination using either -dV/dt or dT/dt is highly recommended for long battery life.  The only TI charger with such termination built-in is BQ2000 controller with external FETs.  We can add another FET to implement direct power path. 

    Regards,

    Jeff  

  • 0 in reply to Jeff F
    Intellectual 525 points

    Hello Jeff,

    In my application, i am using non-removable NiMH battery pack of 3.6V (three 1.2V batteries in series) and USB as a priority power supply.

    Incase, when the battery is discharged to 80% and then I connect USB for power, does the timer for BQ24172 restarts again from 0? In that case, the battery is always overcharged.  Does this IC go to trickle charging mode on overcharging for protection?

    Also, in battery supplement mode what should be min. voltage at  AVCC pin? 

    Thanks in advance

  • 0 in reply to Electro_crazy
    TI__Genius 10385 points

    Jain,

    The battery regulation voltage is is fixed to 4.2V. When the adapter is reconnected, then charging will begin again at fast charge. You will never terminate properly without external circuitry as Jeff has described.

    In supplement mode the battery feeds the system through the body diode of Q3. This will always occur if your adapter voltage is less then VBAT + VFWD of the body diode.

    I hope this helps,

    Ricardo