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BQ2970: DOUT deasserted when battery hot plugged

oneil
Prodigy 95 points
Part Number: BQ2970

Hi TI,

On a design of mine with the BQ2970, I've found that DOUT is sent low when a battery is first connected to my circuit. DOUT goes high as soon as the battery is connected to a charger and stays high even when the charger is removed, regardless of how long the battery was allowed to charge.

I am also noticing that the V- pin is being pulled up so that it is 1.2V less than the BAT pin. These behaviors seem to be consistent with the BQ2970's undervoltage protection. It seems that the UVP is being tripped erroneously because this happens even when a fully charged battery is plugged in. UVP should only be tripped when VBAT- VSS < 2.8V, but this should never be the case with a fully charged battery.

I am wondering if this has something to do with the battery being hot-plugged. Is there any way that I can just plug in a battery and have it work without needing to connect a charger to clear the UVP condition?

Thanks!

  • 0
    Prodigy 95 points

    I was poking around other questions for this part number and found the note on Page 16 of the datasheet noting that shorting V- and VSS / connecting a charger is sometimes needed to get the circuit to work properly.

    Is there any way to avoid this?

    Thanks

  • +1 in reply to oneil
    TI__Expert 8526 points

    Hi Oneil,

    Unfortunately, this behavior has not been characterized, and you will not be able to predict when it will occur.  As stated in the datasheet, after hotplugging the battery, you will need to short V- and VSS or connect a charger to ensure the discharging circuit is enabled.

    Best,

    Andria

  • 0 in reply to Andria McIntyre
    Prodigy 95 points

    Hi Andria,

    Thanks for the reply. Does TI make a similar battery protection IC that does not have this limitation?

    Thanks

  • +1 in reply to oneil
    TI__Mastermind 36020 points

    Hello Oneil,

    No, single cell protectors like this one require either a charger attached or a brief short between V- and Vss (Or PACK+ and BAT+ in the case of the BQ298x family) in order for the device to get out of the initial SHUTDOWN state. 

    The DSG circuitry otherwise may not be enabled during cell attachment. 

    Best Regards,

    Luis Hernandez Salomon