The family-specific AC and DC Characteristics data sheets for Xilinx device families include tables that provide the DC margins for each of the power supply rails, for both Absolute Maximum Ratings (usually Table 1), and Recommended Operating Conditions (usually Table 2).
What are the AC voltage supply margin requirements?
What about ripple voltage for switching regulators?
Some data sheets will provide more specific AC voltage range specifications for a particular voltage rail.
If they do not, it is recommended that the voltage levels for the supply rail, as measured at the device pins, should always be kept within the ranges specified in the DC Characteristics section of the Xilinx family data sheets.
For a partially powered or un-configured device, the voltages including AC noise (and ripple voltage) should be kept within the Absolute Maximum Ratings (Table 1) minimum and maximum levels.
During normal operation, the voltages including AC noise (and ripple voltage) should be kept within the Recommended Operating Conditions (Table 2) minimum and maximum levels.