4.13.1 Sleep Mode and System Power Management

Figure 4-10 shows an example of how power should be supplied in a system that will use the low-power sleep mode of the LAN8670/1/2. In this diagram, VDDAU is provided by a constant supply, so that it is always enabled, even during sleep mode. On system power-up, once this supply is active, the INH pin will be asserted so that its active high output can drive the enable pins of the external switchable supplies for VDDA and VDDP.

Figure 4-10. Sleep Mode Example System

After the device enters sleep mode, the INH pin will enter a high-impedance state. The external resistor will pull the signal down to ground, which will then disable any voltage sources controlled by INH. This can be used to disable power to additional devices, including, when needed, the station host controller.

Important: Before entering SLEEP mode, the desired wake configuration must be configured in the LAN8670/1/2. It is recommended that this mode is configured immediately after a reset. Details can be found in the Configuring Wake section.

Some systems may require a delay between the trigger for the start of sleep mode and disable of the local power supplies, for example, to allow for other nodes on the mixing segment to go quiet. Delay timing is configured with the Sleep Inhibit Delay (SLPINHDLY) field of the Sleep Control 0 (SLPCTL0) register. If wake from the WAKE_IN pin is enabled (WKIEN=1), the WAKE_IN pin must be deasserted before the Sleep Inhibit Delay timer will be started. See Figure 4-11 for a diagram illustrating the timing from when SLEEP state is commanded until the INH pin is released and the SLEEP state is entered.

Figure 4-11. Sleep Timing

In sleep mode, a small amount of current is drawn from VDDAU to monitor for a wake condition. The wake condition can be a WAKE_IN pulse provided from another device, or a signal on the wire harness from another node on 10BASE-T1S network. After a wake condition is detected, INH is actively driven high, enabling the external power supplies, which should be fully powered within 1 ms of INH being driven high according to the OPEN Alliance TC10 Wake/Sleep specification. Once all power supplies are above their thresholds, the LAN8670/1/2 will behave as if it had been reset by the RESET_N pin, and will assert IRQ_N to signal that the LAN8670/1/2 is ready for configuration.

Important: To achieve maximum power savings and allow TC10 power goals to be met when in the SLEEP state, all power supplies except for VDDAU must be powered down.