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BQ25171-Q1: Charge Termination Method

Dice-K
Mastermind 7640 points
Part Number: BQ25171-Q1
Other Parts Discussed in Thread: BQ24400, BQ2002

Tool/software:

Hi support team,

I'm charging 2-cell NiMH batteries.
I believe the only charge termination method for the BQ25171-Q1 is a timer or OVP.

Are there any recent devices that terminate charging by detecting -dV or peak voltage?
I'm hesitant to use the BQ2002/3/4/5 or BQ24400 because they are older devices.

Regards,
Dice-K

  • 0
    TI__Guru* 76376 points

    Hi Dice-K

    Sorry, we do not have a newer NiMH charger with -dV, dt or peak voltage. 

    What is your concern regarding the BQ25171-Q1?

  • 0 in reply to Bill Johns
    Mastermind 7640 points

    Hi Bill,
    Thank you for your reply.

    I would like to charge at a 0.3C rate, but the battery manufacturer recommends detecting -dV.
    If charging is stopped by a timer, I can only use a 0.167C rate, which causes the long charging time to be an issue.

    It would be helpful if there was a way to accurately detect when the BQ25171-Q1 is fully charged when charging NiMH batteries.

    Best regards,
    Dice-K

  • 0 in reply to Dice-K
    TI__Guru* 76376 points

    Hi Dice-K

    Only device we have that could detect -dV would be the one of the BQ2002 devices, but do not recommend due to age and external circuits.

    If you have an MCU with ADC in the system a possibility is using the ADC to measure battery voltage and have MCU manage the battery charge.

  • 0 in reply to Bill Johns
    Mastermind 7640 points

    Hi Bill,
    Thank you for your support.

    I'm charging two AAA NiMH (750mAh) batteries in series.
    According to Table 7-1, the shortest timer setting is 4 hours.
    If I charge at 0.3C (225mA), does that mean the timer won't be able to detect a full charge and I'll have to stop charging using OVP or CE?

    Best regards,
    Dice-K

  • +1 in reply to Dice-K
    TI__Guru* 76376 points

    Hi Dice-K

    Dice-K said:
    If I charge at 0.3C (225mA), does that mean the timer won't be able to detect a full charge and I'll have to stop charging using OVP or CE?

    You should rely on the timer to end charge, if 4 hr is used then charge current would-be C/4. The lower the charge current the better to prevent overheating of the battery and degradation.  

    OVP is less of a charger complete, more of a protection.  Typically, a NiMH will be about 1.5V/Cell during charge and OVP is 1.7V/Cell.