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LM3880: EN pin control circuit suggestion...

Peter Tseng
Genius 5555 points
Part Number: LM3880

Dear Sirs,

As customer design, the major power source is USB 5V, and no any control circuit for EN pin.

While 5V turning off, the EN will be off almost at the same time, and that all FALG outputs will be off together.

Any circuit suggest for EN to make sure the EN will off before 5V while turning off?

Will the voltage divider workable or not?

Thanks. 

  • 0
    TI__Guru 58060 points

    Hi

    The supply voltage(VCC) for LM3880 is 2.7V or above. you have to ensure that the change of the EN happens when VCC is above 2.7V.

    I do not think it can be done by a divider. you have to add a device or external circuit for the following thing:

    1. when the 5V signal is above its own POWER_GOOD threshold, the EN is asserted so that LM3880 can turn on the system

    2. when the 5V signal is below its own POWER_GOOD_OFF threshold(must be > 2.7V), the EN is de-asserted so that LM3880 can turn off the system.

    Regards

    Yihe

  • 0 in reply to yihe
    Genius 5555 points

    Hi SIr,

    Thanks for your reply!

    As customer design, any external circuit suggestion for them to control LM3880 work well?

    BTW, customer saw the rising waveform during turning off, is there any idea about why there is such waveform?

     

    Thanks.

  • 0 in reply to Peter Tseng
    TI__Guru 58060 points

    Hi

    You can use a supervisor or comparator to compare 5V device with a threshold to determine the EN signal.

    The picture is so blurry. It is hard to read the delay between the EN and FLAG output.

    As said in the data sheet, you have to ensure that the EN is low before VCC is below 2.7V. otherwise, the behaviors of the device is undetermined. 

    Regards

    Yihe