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BQ21061: recharge Li-Ion battery under 2V

Francesco Mariottini
Prodigy 140 points
Part Number: BQ21061

Dear

I'm designing a battery charger with your BQ21061 IC and protection circuit with your BQ29707 to recharge a small capacity (about 30mAh) Li-Ion battery. Inside the datasheet of the battery I found that the battery must not be never recharge when the voltage is under 2V. If the device that I'm designing will not be use for a very long time probably will be happen that battery voltage goes below 2V. The protection circuit (BQ29707) open the discharge circuit when battery voltage reaches 2.8V but if the battery will not be recharge for a long time after that protection circuit open the discharge mosfet, could be happen that battery voltage continues to decrease and falls below 2V. Reading the datsheet of BQ21061 I seem to understand that the battery charger attemps to recharge with pre-charge phase also battery with voltage under 2V and therefore this conflicts with the specifications inside the battery datasheet. I would like to know if I well understand datasheet of BQ21061 and, if not, if BQ21061 has a minimum battery voltage under that it doesn't start the recharge process. Or, to avoid that BQ21061 attemps to recharge battery with voltage under 2V, do I need to measure battery voltage with our micro and disable the BQ21061 with the charger enable pin?

Thanks

  • +1
    TI__Genius 10215 points

    Hello,

    Your understanding is correct, if the battery voltage is below VLOWV then the device will attempt to pre-charge the battery at a pre-charge current configured in Register 0x14. It does seem to be the case that, after the discharge FET is disabled at 2.8V, a certain level of current is still consumed that can further discharge the battery after a long time. When an adapter is asserted the charger will attempt to resume charging, and the protection IC will likely re-enable charging as well.

    It seems that the best way to prevent charging as the battery voltage approaches 2V is to disable charging via the CE pin on the BQ21061. It may be more economic, rather than using an ADC is to use the configurable BUVLO threshold as a flag for the microprocessor, such that when a BUVLO fault is detected charging is disabled and when the fault is not detected charging can be enabled.

    Best Regards,

    Juan Ospina