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BQ25171EVM: Technical inquiries during the BQ25171EVM test.

Grady Lee
Expert 2915 points
Part Number: BQ25171EVM

Hi, TI expert.

I have technical inquiries during the BQ25171EVM test by a customer.

I am currently charging with the NiMH 2Cell Series using the BQ25171EVM.

For the BQ25171, it has been confirmed that the charge expires when the charge expiration condition reaches the OVP voltage, or when the time corresponding to the set timer is reached.

A typical NiMH battery recognizes -delta V and ends charging, but in the case of BQ25171, it seems that charging ends only by voltage or time.

The OVP condition is confirmed to be around 1.7V per cell.

In this case, we ask you if you don't need to worry about overcharging the NiMH cell.

Reply please.

Thank you.

  • 0
    TI__Guru 65716 points

    Hello

    This is correct the BQ25171 in NiMH configuration will terminate charge based on timer or OVP voltage.  The timer is set using the CHM_TMR pin to one of 10 possible values.  The OVP is 1.7V per cell and is set using VSET pin to 1 to 6 cell.

    BQ25171 is not a Fast Charge NiMH charger and does not have the option to monitor -delta V or change in battery temp typically used for termination.

    The charge current (ISET pin) should be set to a level along with timer (CHM_TMR pin) that does not stress the battery.  Charge currents will be less than 0.5C vs fast charge which are 1C or greater.

    NiMH batteries are tolerant to overcharge within reasonable limits of current and time.