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BQ21040: Inquiry Regarding Charging Behavior with Dual BQ21040 ICs and USB-C Power Source

Shashank K S
Prodigy 95 points
Part Number: BQ21040

Tool/software:

Hi Team,

I am planning to use two BQ21040 ICs to charge two separate 400mAh LiPo batteries, each at a charging current of 500mA, from a single 5V USB-C power source. To achieve this, I intend to set the CC lines to ground using a 5.1kΩ resistor.

Here are my two power supply scenarios:

  1. Using a PD Compliant Power Source: This will allow me to draw 1A from the source, enabling both batteries to charge at 500mA each in fast charging mode.

  2. Using a Standard USB 2.0 Port: The maximum current cap is 500mA, which is insufficient to charge both batteries simultaneously at 500mA each.

I would like to understand the following:

  1. In a current-limited scenario, how does the charging IC behave when the ISET current is not available at the source?

  2. Since both charging ICs are requesting 500mA from a single source, how would the current be distributed?

I will be testing these scenarios soon (waiting on parts to arrive). In the meantime, it would be helpful to gain a theoretical understanding of the IC's functioning.

Regards,
Shashank

  • 0
    TI__Mastermind 40365 points

    Hello Shashank,

    Please read Section 8.4.2 of the datasheet, it talks about IINDPM and VINDPM and that is what would apply when maxing out the adapter. This also applies to the current distribution question, but the total impedance and layout of the devices will determine which gets more current and which enters DPM first, if both do not enter at the same time. Theoretically having two of the chargers in parallel with the same layout while trying to draw max current would have their DPM responses being active at the same time. Please test according to your application.

    Regards,

    Mike Emanuel

  • 0 in reply to Michael Emanuel35
    Prodigy 95 points

    Hi Michael, 
    Thank you for your response, I have another query, what is the behavior of the charger when a battery is plugged in when charger is on? Would this create problems down the line?

  • +1 in reply to Shashank K S
    TI__Mastermind 40365 points

    Hello,

    There will be charge sharing to/from the output capacitor/battery depending on the voltage. Depending on how the battery is inserted (how fast, through what impedance, etc), will determine how the current/voltage of the OUT pin will behave from this response. In general this should be fine, but I would test according to your application.

    Regards,

    Mike Emanuel 

  • 0 in reply to Michael Emanuel35
    Prodigy 95 points

    Hi Michael,

    Thank you for your response. Will get back to you if I have further queries!

    Cheers,
    Shashank