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How does the BQ24251 (BQ2425x) account for battery self discharge after charge termination?

Jason Work
Genius 10830 points
Other Parts Discussed in Thread: BQ24251

When will the battery be reconnected to the system load using the BQ24251 after it has been fully charged (charge termination enabled)?

I undrestand this will happen when the system voltage (Vsys) drops at least 40 mV below the battery voltage.  However, consider the case when the load does not draw enough current to make the voltage dip and the charger is never disconnected.  The battery will evenutally self discharge without being topped up.  How does the charger account for this?

  • 0
    TI__Expert 7730 points

    Hello Jason,

    Are you talking about the conditions with or without the input power? If there's input power connected and the system power exceeds what the input can provided, then the sys voltage will drop and battery will start supplementing. This is where the 40mV spec applies. When there is no input, system voltage will follow battery voltage and whenever there's current pulling from the system, battery will supplement it as it is the only power resource.

    Thanks,

    Wenjia

  • 0 in reply to Wenjia Liu
    TI__Genius 10830 points

    This did not answer my question.  My question is for when there is input power always.  For the sake of this question, assume the input power is never disconnected.  Also assume that the system load is a maiximum of 100 mA, so it will not exceed 2 A.  After the battery has been charged, and charge termination has taken place, how is the battery charge topped up over time to make up for battery self discharge.

  • 0 in reply to Jason Work
    TI__Expert 7730 points

    If the system load never exceeds the input power then the IC will never be in supplement mode.

    The battery's self discharge is only ~10uA after termination. If for some reason the battery is discharged overtime and the voltage is reduced below the re-charge threshold which is 100mV below battery regulation voltage, the IC will start charging the battery again.

    Thanks,

    Wenjia