If noise in the VCCO PDS is still too high after refining the PDS, the I/O interface slew rate and/or drive strength can be reduced. This applies to both outputs from the FPGA and inputs to the FPGA. In severe cases, excessive overshoot on inputs to the FPGA can reverse-bias the IOB clamp diodes, injecting current into the VCCO PDS.
If large amounts of noise are present on VCCO , the drive strength of these interfaces should be decreased, or different termination should be used (on input or output paths).