LAN8740A - Ethernet PHY Wake-on-LAN (WOL) Feature Clarification
Wake-on-LAN (WOL) is a system power saving feature. It enables the entire system to go to sleep, with the PHY being the only active component. The PHY won't see significant power savings since the PHY is the only chip that is active. The PHY still needs to have all the transmitters, receivers, and PLLs running to maintain the link with the network. It triggers the digital output that can wake up the rest of the system once the magic packet is seen by the PHY. The power savings come from the rest of the system going to sleep.