Why +3.3V regulator when +3.3V available on PCIe connector?

[wisxxx]

The +3.3V step-down regulator on p. 2, C3 has a max current rating of 2 A, for 6.6 W power.

Since the PCIe connector allows for up to 9.9 W for a standard height x4 card, why is there a regulator for +3.3V on the Timing Card?

[ahmadexp]

This is a common practice to not rely on the 3.3v or 5v rails of the PCIe and only use the 12v to make your own voltages. I am open to any suggestions though.

[wisxxx]

It depends on the loading. Do you have any data from the Xilinx Power Estimator for how much current is drawn on the +1.0V, +1.2V, +1.5V, and +1.8V rails?

[wisxxx]

Data available from open source FPGA files.