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BQ21040: Implementing reverse protection circuit with BQ21040

user5108218
Prodigy 130 points
Part Number: BQ21040

I'm using the BQ21040 in my application circuit to charge the Lithium batteries.

The application circuit uses 1 or 2 or 3 single cell lithium ion batteries (3.7 nominal 4.2 full charge) means the user can operate the circuit using one 18650 or 2x 18650 or 3x 18650 batteries. The application doesn't come with a 1S3P pack.

To avoid reverse polarity and to protect the application circuit, the following circuit is implemented. Could you please get a validation for the design below.

Parallel protection is discussed over this thread.

  • 0
    TI__Guru* 75886 points
    Sorry for the delay getting back to you on this question.
    The Reverse Protection circuit looks OK. A possible problem condition would be a deeply discharged battery.
    The bq21040 charging circuit looks OK.
  • 0 in reply to Bill Johns
    Prodigy 130 points
    Thanks Bill,

    So the discharging circuit works fine.
    Reverse polarity also works fine.

    What is not working is the battery charging. The battery protection gets triggered when 5V USB is plugged.

    I'm using Samsung 18650 batteries 2600mAh.

    Current draw is around 150-200mA.

    I used a battery from 4.1 to 3.5v. after plugging the USB (5V), even after keeping the device plugged in for 4hrs, the battery doesn't charge.

    Observations
    When the battery is not connected, the battery pack + and pack - shows 3.9v.
    Output of the charging IC also shows 3.9v.

    When the battery is connected, output of the charging IC shows 3.9v whereas the voltage across the battery shows 3.5v.

    Could you please assist in solving the issue.
  • 0 in reply to user5108218
    Prodigy 130 points
    Hey Bill, any thoughts? My production is stalled for the battery issue.

    Please advise.
  • 0 in reply to user5108218
    TI__Guru* 75886 points
    Hello
    When this happens:
    1.) What is input current?
    2.) Is /CHG high or low?
    3.) What is voltage at ISET?