The LAN8720A/LAN8720Ai is a low-power 10BASE-T/100BASE-TX physical layer （PHY） transceiver with variable I/O voltage that is compliant with the IEEE 802.3-2005 standards. The LAN8720A/LAN8720Ai supports communication with an Ethernet MAC via a standard RMII interface. It contains a full-duplex 10-BASE-T/100BASE-TX transceiver and supports 10Mbps （10BASE-T） and 100Mbps （100BASE-TX） operation. The LAN8720A/LAN8720Ai implements auto-negotiation to automatically determine the best possible speed and duplex mode of operation. HP Auto-MDIX support allows the use of direct connect or cross-over LAN cables. The LAN8720A/LAN8720Ai supports both IEEE 802.3-2005 compliant and vendor-specific register functions. However， no register access is required for operation. The initial configuration may be selected via the configuration pins as described in Section 3.7， “Configuration Straps，” on page 29. Register-selectable configuration options may be used to further define the functionality of the transceiver. Per IEEE 802.3-2005 standards， all digital interface pins are tolerant to 3.6V. The device can be configured to operate on a single 3.3V supply utilizing an integrated 3.3V to 1.2V linear regulator. The linear regulator may be optionally disabled， allowing usage of a high efficiency external regulator for lower system power dissipation. The LAN8720A/LAN8720Ai is available in both extended commercial and industrial temperature range versions. A typical system application is shown in Figure 1-1.