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bq24040 - The function of nCHG-terminal

Dice-K
Mastermind 7500 points
Other Parts Discussed in Thread: BQ24040

Hello,

When I applied the voltage "out of the charging range (4.0V - 4.4V)" to IN-terminal,
the charging does not occur, but nCHG-terminal becomes Low
Is this function correct?

Regards,
Daisuke

  • 0
    TI__Genius 13700 points

    Hello Daisuke-san,

    How do you have the circuit configured? If you have the diode and resistor connected to the output just like schematic below?

    If this is the case the potential on the /CHG pin will be low because the input is below the operation point meaning there is no voltage on the output.

    When you have the input voltage between 4.0-4.4V can you measure the OUT pin and the /CHG pin?

  • 0 in reply to Ryan May
    Mastermind 7500 points

    Hello Ryan.
    Thank you for your reply.

    The input voltage is between 4.0-4.4V
    When I connect a battery,
    OUT-terminal is the battery-voltage.
    And /CHG pin is 0V.
    Is this function correct?

    Best regards,
    Daisuke

  • 0 in reply to Dice-K
    TI__Genius 13700 points

    Hello Daisuke-san,

    The fact that the OUT pin is measured at the battery voltage when the battery is connected makes sense even if the BQ24040 is off since the battery biases that net.

    What do you have connect to the /CHG pin? Do you have it configured just like the application schematic in the above post?

    I just tested a case with Vin<4.4V and a battery attached to the EVM. The /CHG & /PG were pulled low. This is a result of the Vin being above the UVLO of 3.4V and also being above the battery voltage. This places the device in a state where it is attempting to charge but since the input voltage is below the Vindpm threshold charging is is paused wanting for the input voltage to rise high enough.

    All this to say what you are seeing is expected operation for the BQ24040. While charging is indicated the BQ24040 is attempting to protect the input source by reducing the charging current until the input source rises above the threshold.

    Let me know if you have any other questions.