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USB Power?

MikeH
Guru 15580 points

I am designing a project using the C5515. I do not plan to use the USB module in my application. Do I need to connect any of the USB power pins to either power or GND?

  • 0
    TI__Expert 5745 points

    Hi Mike,

    From the c5515 datasheet, if you are not using the USB subsystem, then the Core, PHY and I/O supplies can be powered down.

     Datasheet: http://www.ti.com/lit/ds/sprs645e/sprs645e.pdf (pg.78)

    The LDOI pins must always be powered on. The USB_VDDxxx pins should be connected to ground if not in use (pg. 45 of datasheet).

     

  • 0 in reply to Keegan@TI
    Guru 15580 points

    Thanks Keegan. Saved me hours of searching.

  • 0 in reply to MikeH
    Guru 15580 points

    Keegan (or anyone else who can answer).

    Would it hurt to leave one of the 3 LDOI pins (i.e. F13) floating? We inadvertently tied it to ground and can cut the trace to the BGA pin F13, but can't reconnect F13 to another pin (no way to add a trace that small). Are F13, F14, and B12 all tied together in the die?

  • 0 in reply to MikeH
    TI__Expert 5745 points

    Mike,

    Wish I could give you some good news, but I cannot recommend floating those pins as the pins source not only the LDOS but many of the on-chip peripherals and PLLs through those LDOs. My guess is that these input pins are not tied together in the die, but I could be wrong there.

  • 0 in reply to Keegan@TI
    Guru 15580 points

    Keegan,

    Thanks for the feedback, but I really have no choice but to try. To clarify, per the initial question in the thread, I have grounded all of the USB peripheral VDD pins since I do not plan to use the USB section. So, hopefully the USB_VDD LDOI pin (which appears to be tied to the other LDOI inputs since grounding it shorts the others to ground) is simply another current source for the USB section and is tied to the other LDIO pins inside the chip. 

  • 0 in reply to MikeH
    Guru 15580 points

    For those of you who have made similar design errors on a BGA-based device like the C5515, I had the board re-worked by a group in the Chicago area by the name of BEST (Business Electronics Soldering Technology - http://www.solder.net/). They removed the C5515, cut the trace that was shorting the USB_VDD_LDOI pin to ground, and added a trace to the correct adjacent pad, and installed a new C5515. THE BOARD NOW WORKS FLAWLESSLY! The process was fairly painless (other than my high anxiety) and was turned around in a week.

    I just wanted to let everyone know that a BGA layout error is not necessarily a catastrophic event....:)

    Happy DSP-ing!

  • 0 in reply to MikeH
    TI__Expert 5745 points

    Fanstastic news Mike! Thanks for providing your solution!