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Contributor
Contributor
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Registered: ‎11-24-2009

Unused MGTREFCLK pins

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Hello,

I'm working on a Kintex Ultrascale FPGA PCB design with a requirement that no pins are to be left floating.  I'm having trouble with the MGTREFCLK pins, as UG576 instructs to leave unused MGTREFCLK pins floating.  Is it safe to connect these to ground?

Thanks,

Pete.

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Teacher
Teacher
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Registered: ‎07-09-2009

Re: Unused MGTREFCLK pins

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why no pins to be left floating ?

if you must connect them, try 10nf to ground, it will do no harm and meet your design constraints.

Do not ground the pins, as they have internal bias,
<== If this was helpful, please feel free to give Kudos, and close if it answers your question ==>

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Teacher
Teacher
312 Views
Registered: ‎07-09-2009

Re: Unused MGTREFCLK pins

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why no pins to be left floating ?

if you must connect them, try 10nf to ground, it will do no harm and meet your design constraints.

Do not ground the pins, as they have internal bias,
<== If this was helpful, please feel free to give Kudos, and close if it answers your question ==>

View solution in original post

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Contributor
Contributor
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Registered: ‎11-24-2009

Re: Unused MGTREFCLK pins

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Thanks for this John. The reason for not leaving floating pins is to avoid a buildup of static on disconnected copper. I see from Figure 5-6 of UG 576 that the bias is through 50 Ohms to 4/5 MGTAVCC. Seeing that I'm already powering this supply, this means that I am actually safe to leave these disconnected.

Many thanks!
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Teacher
Teacher
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Registered: ‎07-09-2009

Re: Unused MGTREFCLK pins

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I agree,

 

but I bet every time that circuit gets reviewed some one will object to "floating" pins,

  suggets big not eon Schematic next to pin spointing at the data sheet reference page.

 

<== If this was helpful, please feel free to give Kudos, and close if it answers your question ==>
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