VREF Stabilization Capacitors

In V_REF supply stabilization, one capacitor per pin is placed as close as possible to the V_REF pin. The capacitors used are in the 0.022 µF – 0.47 µF range. The V_REF capacitor’s primary function is to reduce the V_REF node impedance, which in turn reduces crosstalk coupling. Since no low-frequency energy is needed, larger capacitors are not necessary.

This only applies when Internal V_REF is not used. Internal V_REF is an UltraScale architecture feature wherein the reference voltage rail is generated internally. See UltraScale Architecture SelectIO User Guide (UG571) [Ref 10] for more details on Internal V_REF.