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XCLKOUT layout when it's not used in F280x

Ricky Zhang
Genius 9520 points

Hi, Champs,

We can find below statements at page 6 in literature "Hardware Design Guidelines for TMS320F28xx and TMS320F28xxx DSCs" (SPRAAS1A):

This(XCLKOUT) is an output pin of the CMOS device and should not be terminated to ground even if it is not used.

 

Customer might want to know how should we handle it when layout? When it's used or unused, should it be pull-up, pull-down, or left un-connected?

Thanks for your comfirmation, and happy new year!

 

Best regards,

Ricky Zhang

  • 0
    TI__Guru* 95315 points

    Ricky,

    On "older" devices, XCLKOUT is a dedicated pin and your question is pertinent to such devices only. On Piccolo devices, XCLKOUT function is multiplexed with GPIO function and by default, the pin comes up with the GPIO function enabled. Here are some thoughts on how to handle this (dedicated) pin:

    Case 1: XCLKOUT pin is used in the customer application, perhaps to provide the clock signal for another device --> How this pin should be handled (in terms of buffering, impedance matching on the PCB layout to preserve waveform integrity etc) is determined by the application design. This is done on a case-by-case basis.

    Case 2: XCLKOUT pin not used--> In this case, it would be prudent to turn this pin off, for 2 reasons: (1) To conserve power on the VDDIO rail (2) To minimize electromagnetic emissions due to the toggling of this pin. Since this is a output only pin, it may be left unconnected.

  • 0 in reply to Hareesh Janakiraman
    TI__Genius 9520 points

    Hareesh,

    Yes, I'm just talking about the XCLKOUT pin in Piccolo-previous devices here, and thanks for your confirmation on this issue.

     

    Best regards,

    Ricky Zhang