When you see Ethernet PHY chips' application circuit, you can find out the difference about connecting center tap of transformer.
Some PHYs should be connect to the DC power but some don't connect to it.
The following circuit diagram is for LAN8720a interface circuit.
It should be connected to the AVDD directly (Case A in the image).
But some other PHY application circuits are different (Case B).
Now, I have some questions:
Why application circuits are different according to the PHY?
What is happenning if I connect the center tap to the power for the Case B PHY?