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BQ24079: Output does not start when the battery is not connected

Yamaomaru Masanori
Prodigy 10 points
Part Number: BQ24079
I'm trying to boot with power from USB with the battery disconnected.
The output load is connected to a boost converter.
However, no voltage is output even if USB is connected.
This can be improved by pulling up EN2 once via USB.
Alternatively, it can be improved by disconnecting the boost converter.
What kind of measures are necessary for the voltage to be output normally?

  • 0
    TI__Mastermind 23200 points

    Hi,

    How much current is the boost converter using? It sounds like this may be a short circuit is being detected due to EN2 being connected to OUT initially. An alternative is to pull EN2 to the IN pin.

    Best Regards,

    Anthony Pham

  • 0 in reply to Anthony P Pham
    Prodigy 10 points
    The boost converter is flowing 500mA.
    Therefore, it seems that a short circuit was detected.
    As advised, I connected EN2 by pulling it to the IN pin.
    However, the output stops with the same operation.
    Also, in rare cases, it may be output normally.
    It does not work stably.
    Is there a way to deal with it without lowering the output current?
  • 0 in reply to Yamaomaru Masanori
    TI__Mastermind 23200 points

    Hi,

    Interesting, ok. Can we try increasing the capacitance on the OUT pin? Would you be able to provide waveforms on the input and output voltages?

    I also see that you have configured the charge current to about 1.4A and the input current to 1.4A. Can we reduce the charge current so that there is enough current going to the output (reduce current to about 1A). The device would be reducing the charge current due to DPPM since it cannot supply the combined 1.9A being consumed by the output and the battery but this may help reduce the chances of short circuit on the output. 

    Best Regards,

    Anthony Pham

  • 0 in reply to Anthony P Pham
    Prodigy 10 points

    I tried to increase the capacity of the OUT pin as advised.
    The output became stable by increasing it to 220 μF.
    It was unstable at 100 μF.
    It may have been affected by the switching noise caused by the boost converter.
    Using 220μF solved this problem.
    Thank you for your advice.