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BQ21040: VIN-DPM lower current limit

Jomon
Intellectual 660 points
Part Number: BQ21040

BQ21040 has Vin-DPM voltage set at 4.3V.

Consider the BQ21040 charging the battery from a common rail, which is also connected to other devices. The input can only source 500mA and the other device connected to the rail is taking up the 500mA approximately. This leaves almost no current left for the BQ21040 to charge the cells. The voltage would now be near 4.3V as well.

So, in this case, does BQ21040 stop charging until there is enough current available ? What if the current available is only 50mA on the rail ?

Thanks in advance.

  • +1
    TI__Expert 8315 points

    Hi,

    The device will use whatever available charge current is still on the common rail. If there is only 50mA available, the input current and charge current will both be limited to 50mA. The device will not stop charging completely, but charge rate will be greatly reduced.

    ThBQ21040 will also begin to reduce input current as VIN approaches 4.3V (VINDPM). ICHG is reduced through this process as well because ICHG can not exceed IIN. 

    Best Regards,

    Jackson

  • 0 in reply to Jackson DiGiovanna
    Intellectual 660 points

    Hi Jackson,

    Thanks a lot for the clarification.
    Can you please clarify the following as well,
    How much is the minimum charge current that the device will operate at with the VINDPM limit of 4.3V (when the charger is fully loaded in this scenario) ? Is it 50mA or can the device charge at much lower rate ?

    Thanks in advance.

  • 0 in reply to Jomon
    TI__Expert 8315 points

    Hi Jomon,

    As you approach VINDPM, the input current will taper out. This being said, the device will be able to charge at a much lower rate. As I reduce VIN, the voltage tapers to 50mA around 4.3V but will taper further as I keep lowering VIN past the point where it reaches 50mA.

    Thanks,

    Jackson