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ILIM mode change with bq24079

FrankXu
Genius 3500 points
Other Parts Discussed in Thread: BQ24079

I use C6748 dsp to control bq24079's EN2\EN1 pin as shown in the figure. The system is powered with a 3A power supply, current limit is set to 3A.

At first the GPIO1 output 0 and GPIO2 output 1, so the bq24079's EN2EN1=01 and it's in 500mA mode.

Then I use DSP to swith GPIO2 to low, so the bq24079's EN2EN1=00 and it swith into 100mA mode.

But I capture a short-time(<100ns) voltage drop in VCC_BATT which is the output of bq24079, and that makes the DSP disconnected from the emulator.

Q1: Is this normal for bq24079?

Q2: I want to make the system can be powered by a 500mA-USB or by a 1.3A adaptor. How to make the system self-adaptive to the two power supplies?

       If I set the EN2EN1=10 and when customer connect the system with a 500mA-USB, the USB's output voltage will drop, which may damage the customrer's USB master devices. But I really want to have a 1.3A charging current when the system is connected to a 1.3A adaptor.

       How to realize that?

       

  • 0
    TI__Mastermind 20570 points
    What is the load profile look like on OUT pin? Can you try increase the capacitance on C60?
    Can you provide scope captureS on the issue you described above? Please include EN1, EN2, IOUT, VOUT.
  • 0 in reply to Jing Zou
    Genius 3500 points
    Hi Jing Zou,
    Thank you very much.
    I found there is a bug on the pull up of my GPIO. Now the problem is solved.
    For the 2nd question, do you have any suggestion?
    Q2: I want to make the system can be powered by a 500mA-USB or by a 1.3A adaptor. How to make the system self-adaptive to the two power supplies?

    If I set the EN2EN1=10 and when customer connect the system with a 500mA-USB, the USB's output voltage will drop, which may damage the customrer's USB master devices. But I really want to have a 1.3A charging current when the system is connected to a 1.3A adaptor.

    How to realize that?
    Thank you.
    Frank
  • 0 in reply to FrankXu
    TI__Mastermind 20570 points
    The IC does not dynamically change the input current limit setting. You will have to use external USB detection to notify your host to change the EN1 and EN2 setting accordingly.