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L138 USB0_VDDA33 Supply

tehoaislimau
Intellectual 360 points

Hi

I have a L138 application where all the DVDD IO voltages are powered by 1.8v and Core/PLL at 1.2v.

This design also uses Li-Ion batteries.

Can I turn off my 3.3v regulator, powering only the USB0_VDDA33 supply when USB module is turned off and not in use?

This will eliminate the need for a buck boost regulator just for USB, and I can source the supply from the USB 5v port itself.

  • 0
    TI__Guru**** 178316 points

    Would you please share with me your power-up, power-down sequence? If not using the buck boost regulator to supply 3.3V to USB0_VDDA33, how do you plan to supply 3.3V from the 5V VBUS?

    Thanks

    David

  • 0 in reply to David (ASIC) Liu
    Intellectual 360 points

    Hi

    Attached is the power management tree.

    As you can see, the power regulator is a switching buck regulator that provides the 1.2v and 1.8v to the L138.

    The power up sequence is from the lowest, then highest, i.e. 1.2v first then 1.8v.

    If there is a need for USB communication, only then upon plugging in from the computer USB hub, the 5V external would provide another 3.3v LDO to source the USB_VDD33 to OMAP.

    Is this okay.

  • 0 in reply to tehoaislimau
    Intellectual 360 points

    Hi, anybody from TI can comment on this implementation?

    The documentation does state that if the USB0 module is being turned off, the supplies can be removed; but I wanted to make sure no issues with this.

  • 0 in reply to tehoaislimau
    TI__Guru* 84075 points

    Hi Faisal

    We discussed this internally, and unfortunately the way you are trying to use , is not the intended use-case.

    We only support USB 1.8 and 3.3V being off together (as would be the use-case when users are not using USB0 in their design). We cannot recommend just turning portion of the USB PHY power for extended period of time or otherwise, as there is no in-built isolation to allow one of the supplies to be turned off etc.

    Regards

    Mukul