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BQ24650: Why is BQ24650 limited to connect only 1~6 cells?

Francis Jiang
Expert 3310 points
Part Number: BQ24650

Hi Team,

The battery charge voltage (Max) of BQ24650 is 26V, and usually lead-acid battery single-cell voltage is 2V, it seems that a maximum of 10+ cells can be connected. So, why is BQ24650 limited to connect only 1~6 cells?

Best Regards,

Francis Jiang

  • 0
    TI__Expert 3310 points

    And when the device is used for lead-acid battery, in addition to the referenced hardware design, are there any additional requirements for the application of lead-acid battery? For example, the minimum voltage cannot be lower than a certain value.

  • 0 in reply to Francis Jiang
    TI__Mastermind 40905 points

    Hello Francis,

    The cell count is in reference to the generic 4.2 V/Cell. The total maximum charge voltage is 26 V.

    In general for the lead-acid we recommend to make sure to follow the recommended charge profile for the selected battery and we recommend keeping in mind the temperature impact on charge voltage regulation to lengthen the battery life.

    As for the minimum charge voltage the minimum charge voltage is 2.1 V.

    Regards,

    Mike Emanuel

  • 0 in reply to Michael Emanuel35
    TI__Expert 3310 points

    Hi Mike,

    Thanks for your reply. It helps a lot.

    Could you please help me further to understand what is charge voltage and recharge voltage threshold (PF pin) in BQ24650? And how the device changes CC mode to CV mode (internal action)? Thanks.

    Best Regards,

    Francis Jiang

  • 0 in reply to Francis Jiang
    TI__Mastermind 40905 points

    Hello Francis,

    Glad I could help!

    The charge voltage regulation is 2.1 V on the VFB pin. This means you connect a resistor divider from the battery to the VFB pin such that the VFB pin is 2.1 V when the battery has full charge voltage. The recharge threshold is typically 2.05 V on the VFB pin, which means it would be lower than the full charge voltage at the battery by the resistor divider calculation.

    Once the VFB pin reaches 2.1 V the charger leaves CC mode and enters CV mode. Here the charger current is tapered off until termination. 

    Regards,

    Mike Emanuel