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PCI - decoupling of unused 3.3V connector pads
Hi pci-sig members,
I am currently designing a PCI add-in card PCB,
and have been reading "PCI Hardware and
Software Architecture and Design, 4th edition".
Chapter 13 on Connector, Platform, and Add-In
Card Design, has useful info on layout and
decoupling issues. However, the last dot
point of the chapter has me scratching my head.
"All unused 3.3 volt and 5 volt connector pads must
be individually attached to a 0.01 uF high speed
capacitor.... Several connector pads can share a
capacitor if trace requirements are met".
For this design, I am actually not using the 3.3 volt
from the PCI connector. However, the above
implies that I should still decouple these pads.
Is that correct? If so, what is the reasoning behind
needing to decouple those pads if I am not using
the 3.3 volt supply on this card?
Thanks for considering my question.
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