2.3 Example Systems

A simple system-level block diagram for the LAN8650/1 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. When using the LAN8651 which has an internal voltage regulator, no external 1.8V supply is needed.

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 as is the 1.8V supply, required when using the LAN8650. In this particular system, the host will initiate sleep mode and then ensure that all inputs to the LAN8650/1 are high-impedance. In a system where external power supplies are required to remain active while other devices shut down, the LAN8650/1 can drive the INH pin for a programmable delay period before entering sleep mode. In this example, the host will bring the LAN8650/1 out of sleep using WAKE_IN and other devices can then be awakened via WAKE_OUT. The advanced features available on the DIO pins are also available to the host microcontroller in this system.