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BQ24725AEVM-710: Not charging SMBUS 1.1 battery

Chandler KI
Prodigy 190 points
Part Number: BQ24725AEVM-710
Other Parts Discussed in Thread: BQ24725A

Hello,

I am testing the BQ24725A-EVM with a SMBUS 1.1 compliant smart battery. I assumed the EVM would be plug and play with the smart battery, and automatically begin charging, but that's not the case.

I see no data on the SMBUS lines, only a constant 3.3V, so there seems to be no communication with my smart battery and the BQ24725A charger.

I thought the battery would act as a host and send commands to the charger. Do I need to establish some kind of initial communication on the SMBUS so the charger can begin charging the smart battery?

Thank you.

  • +1
    TI__Genius 11850 points

    Hi Chandler,

     

    The BQ24725A operates only as a SMBus slave device, and it does not initiate communication on the bus. Since the ChargeVoltage() and ChargeCurrent() register settings are both zero at POR, charging will not begin until the host MCU or smart battery writes to the ChargeVoltage() and ChargeCurrent() registers.

     

     

    Best regards,

    Angelo

  • 0 in reply to Angelo Zhang87
    Prodigy 190 points

    Angelo,

    Ok that makes sense. So if my smart battery does not automatically broadcast the ChargeVoltage() and ChargeCurrent() to the BQ24725A address, like some TI-fuel gauges do, then my host MCU will need to initiate charging by writing to the smart charger, correct?

    Our smart battery is a sealed unit and we are to not modify any of its content, so I suppose we will have to use the host MCU to request the Charging Current and Charging Voltage from the smart battery and then write those values to the BQ24725A.

    Thanks.

  • +1 in reply to Chandler KI
    TI__Genius 11850 points

    Hi Chandler,

     

    Yes, your understanding is correct. In this case, your host MCU must write to the BQ24725A's ChargeVoltage() and ChargeCurrent() registers in order to begin charging.

     

    Best regards,

    Angelo

  • 0 in reply to Angelo Zhang87
    Prodigy 190 points

    Thanks for the quick response Angelo.