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BQ25619: Understanding BAT Depletion Threshold

stomp
Genius 4675 points
Part Number: BQ25619

Hi,

I am trying to understand the battery depletion threshold values of BQ25619.

I refer to page 9 of SLUSDF8B.PDF (June 2019).

I have a BQ25619 conected to a Li-Ion cell and when the cell voltage drops below 2.60V, the BQ25619 turns off the BATT_FET, this works as expcted.

I also notice that when my cell is hovering around 2.5V, the BATFET is switched on, I'm assuming some threshold is reached between 2.35V and 2.8V.

The BQ25619 powers up and poweres down depending on how the cell is recovering during this critical voltage region.

I'd like to know if the MAX vlaues for the BATFET depletion threshold will both hold true for ON and OFF conditions for a given temperature or process variation.

For example BATFET is off below 2.62V, should it not also be on for 2.8V or are the ON and OFF values not related?

Thanks.

Thanks.

  • 0
    TI__Guru 57551 points

    Hi,

    The d/s has listed the spec ranges. The rising and falling specs are applicable to the same device.

    Thanks,

    Ning.

  • 0 in reply to Ning T
    Genius 4675 points

    Hi Ning,

    Thanks for your help.

    We have an issue where our device in the field depletes its cell below about 2.5V and when re-powering the hardware, the cell does not start charing, and the BQ25619 as no output.

    We were wondering if the condition is related to being in some unknown state between the two conditions that turn BATFET ON.

    Could you provide any insight into what prevents the BQ25619 from charging our cell and starting up correctly with a low cell voltage of 2.5V?

    Thanks.

  • 0 in reply to stomp
    TI__Guru 57551 points

    Hello,

    Is there any battery protection circuitry in between the BAT pin and the battery pack or does the battery have built-in battery protection? The battery protection may disconnect the battery from the BAT pin of the charger under certain conditions.

    Thanks,

    Ning.

  • 0 in reply to Ning T
    Genius 4675 points

    Hi,

    We have an 18650 Li-Ion cell, no protection mechanisms in it.

    We can deplete the cell and the BQ25619 turns off. When we power the hardware (via the adpater) it can take 2 or 3 attempts before the BQ25619 will power on and enable the system bus power.

    We feel that this condition is caused by the 18650 cell just slightly recovering and then drooping again under initial load.

    I don't know there is a solution to the issue, but its more of an annoyance that the user needs to power cycle our device a few times if they cell were to run flat.

    Thanks.