2.3 Example Systems

This section shows example of system block diagrams that apply to all family members.

Note: All family members support advanced features such as ACMA and signals for time synchronization, but they are not shown below since the pin configurations vary among the family members.

Note: The clock source for MII is a crystal connected between pins XTI and XTO. The clock source for RMII is a clock oscillator that is connected to REFCLKIN on both the MAC and the PHY. Additional information is available in the Pin Descriptions section.

An example system-level block diagram for the LAN8670/1/2 is shown in Figure 2-2, below. This system does not use sleep mode, so VDDA and VDDAU can be treated as the same supply and VDDP must only be properly isolated from the analog supplies through use of a ferrite bead as described in the Power Connectivity section.

Figure 2-2. Simple System Using LAN8670/1/2

Figure 2-3 shows a system which is designed to use the low power sleep mode so the constant voltage supply VDDAU is separate from the other voltage supplies. VDDA and VDDP will be disabled in sleep mode. In this particular system, the external MCU will initiate sleep mode and then ensure that all inputs to the LAN8670/1/2 are high-impedance. In a system where external power supplies are required to remain active while other devices shut down, the LAN8670/1/2 can drive the INH pin for a programmable delay period before entering sleep mode. In this example, the external MCU will bring the LAN8670/1/2 out of sleep using WAKE_IN and other devices can then be configured to be awakened via WAKE_OUT or activity on the MDI. When the LAN8670 is in the MII or SC-MII mode, WAKE_OUT is not available.

Figure 2-3. System with Sleep Mode Using LAN8670/1/2