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BQ25619: Isys while battery fully charged

Leonardo Sandler
Prodigy 160 points
Part Number: BQ25619

Hi, 

I would like your feedback to understand how the bq25619 behaves in the following 2 scenarios:

1) We have a scenario application in which the battery charger is always connected to a power source at Vbus. 
In this scenario, our device is continuously connected to the external power source. And the device is functional, meaning there is a continuous current consumption from the Vsys output (Isys). 
The battery is always connected, so the bq25619 will charge the battery continuously. 
At some moment, let's say after 2 hours, the battery will be fully charged, and the device will continue being functional.
In this condition, we would like to stop the charging process, to reduce the use of the battery. 
We would like to know if the bq25619 device has some expected behavior for the case the external source is always connected, we have continuous load connected, and the battery is fully charged. 
Do we have a way to disconnect the battery to avoid continuous charging ?

2) Another scenario si Overnight charging.
In this scenario the device is turned off and we have a very low Isys current (off-state). 
In this scenario the battery will reach a fully charged state, and there is low Isys consumption. What is the expected behavior for this case? 
What would happen for overnight charging?

Thanks,
Leonardo

  • 0
    TI__Guru 50641 points

    Leonardo,

    1) The BATFET can be turned off by setting BATFET_DIS (REG07[5])  to 1. Please refer to 8.3.7.1 BATFET Disable (Enter Ship Mode) on the d/s for the details.

    2) Please refer to 8.3.2 Device Power Up From Battery Without Input Source on the d/s for the details.

    Thank you very much,

    Ning.

  • 0 in reply to Ning T
    Prodigy 160 points

    Hi Ning, 

    1) I see in section 8.7.3.1 the following sentence:

    To extend battery life and minimize power when the system is powered off during system idle, shipping, or
    storage, the device turns off BATFET so that the system voltage is floating to minimize the battery leakage
    current.

    I understand that entering the charger in shipping mode is not the desired solution. 

    We don't want the system voltage to be floating. We want the Vsys working because the system should be functional.

    In section 8.3.6.3 I see the following sentence: 

    The device terminates a charge cycle when the battery voltage is above the recharge threshold, and the current
    is below termination current. After the charging cycle has completed, the BATFET turns off. STAT is asserted
    HIGH to indicate charging is done. The converter keeps running to power the system, and BATFET can turn on
    again to engage Section 8.3.5.3.

    So it seems that the bq25619 performs automatically the desired behavior. 
    The load system connected to Vsys will continue working after the battery is completely charged, and the BATFET will be turned off if the battery is completely charged. And this will be performed automatically by the charger without any required configuration.

    Is this correct?

    2) It seems that I didn't explain very well our concern. Section 8.3.2 does not refer to the scenario I intended to describe. 

    I'm asking when the external input source is connected to the charger, for instance if I leave the charger connected all night long. 

    What happens with the charging process? Should I refer to the same section 8.3.6.3 ?

    Thanks,

    Leonardo

  • 0 in reply to Leonardo Sandler
    TI__Guru 50641 points

    Leonardo,

    1) When the charge is terminated, the BATFET is turned off from SYS to BAT, i.e. the current can't flow from SYS to BAT. The battery may still discharge from BAT to SYS.

    2) Please refer to both 8.3.6.3 and 8.3.6.1 Autonomous Charging Cycle.

    Thanks,

    Ning.