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Permissible connections to unpowered USB on C6747

Other Parts Discussed in Thread: TMS320C6747

The background to my question is that I am trying to specify connections that will be compatible across a range of products.

Suppose the 1.8V USB power supply is not provided on my board and none of the USB power pins (USB0_VDDA33, USB0_VDDA18) are connected and there is no filter capacitor on USB0_VDDA12.  Is it nevertheless permissible to connect USB0_VBUS to +5V, USB0_DRVVBUS through a 1.5K pullup to +3.3V, and USB0_ID to ground?  Or must some or all of these pins be left unconnected?

(BTW when I enter the part number TMS320C6747 it forces the "Select a forum" dropdown to be "C64x Single Core DSP Forum", and that is not correct!"  I checked "I don't have a part number" so this post could show up in the correct forum.)

  • Hi Debora,

    I've forwarded this to the hardware experts. Their feedback should be posted here but could you give more details about your board, is it a custom board?

    BR
    Tsvetolin Shulev
  • Hi Tsvetolin,

    Thanks for looking into it. Yes, it is a custom board. The USB power switch, diodes, and connector are mounted on another board and the VBUS, DRVVBUS, ID, DM, DP nets are carried through a board-to-board connector. The problem is that different component population options are planned for the processor board - USB 1.8V supply and caps would be stuffed or not depending on the intended processor board features. So my question is about mixing and matching the two boards - would a processor board that's populated for no USB be damaged if it is mated with a connector board that puts +5V on VBUS?

    Regards,
    Debora
  • Deboara,

    If you are not using the USB peripheral, you may required to leave all the pins unconnected as given in section 3.6.23 Unused USB0 (USB2.0) and USB1 (USB1.1) Pin Configurations in data manual. Partial connection as you mentioned in your post is not acceptable and it would lead to damage the peripheral.

    Regards,
    Senthil