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EdJ
Visitor
Visitor
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Registered: ‎07-15-2020

Unused GTH power group

I am using a KCKU035-FFVA1156.  The pinout of this package shows an L power supply group, but the 035 doesn't have any L side GTH quads.  I believe the pinout is for migration to the KCKU060 in the same package. 
 
UltraScale Architecture GTH Transceivers User Guide (UG576) says that "If all of the quads within a PSG are not used, the associated power pins can be left unconnected or tied to GND".
 
Since there are NO L side GTH quads in the 035, do I need to connect the L side GNDs to the PCB?   There are many GND pins (46) for the L power supply group at the edge of the package and I have to route a large number of differential signals past the GND vias if I do connect them.   Is there any reason why I have to connect these GNDs?   If a ground connection is necessary to keep a plane from floating, can I connect sets of GND pins together with a trace on the top layer and use one via for each set?  Is there a single GND plane on the FPGA for the power supply group?  If so, I could just tie one GND pin to the PCB to keep the plane from floating.
Does the 035 die have anything of the L side power group on it?  If nothing, the GND connections cannot be important.
 
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roym
Moderator
Moderator
382 Views
Registered: ‎07-30-2007

I would definitely ground it and not leave it floating but beyond that I don't have experience with this.  




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