7.1 Overview

The TPS23861 is a four-port PSE for power over ethernet applications. Each of the four ports provides fully automatic detection, classification, protection, and shut down in compliance with the IEEE 802.3at standard.

The schematic of Figure 36 depicts automatic mode operation of the TPS23861, providing turnkey functionality ready to power PoE loads. No connection to the I²C bus or any type of host control is required. In Figure 36 the TPS23861 automatically:

1. Performs four-point load detection.
2. Performs classification including type-2 (two-finger) of up to Class 4 loads.
3. Enables power with protective foldback current limiting, and ICUT value based on load class.
4. Shuts down in the event of fault loads and shorts.
5. Performs Maintain Power Signature function to ensure removal of power if load is disconnected.
6. Undervoltage lock out occurs if VPWR falls below V_{PUV_F} (typical 26.5 V).

Following a power-off command, disconnect or shutdown due to a start, ICUT or ILIM fault, the port powers down. Following port power off due to a power off command or disconnect, the TPS23861 will continue automatic operation starting with a detection cycle. If the shutdown is due to a start, ICUT or ILIM fault, the TPS23861 enters into a cool-down period. After the end of the cool-down period the TPS23861 continues automatic operation starting with a detection cycle.

The TPS23861 will not automatically apply power to a port under the following circumstances:

• The detect status is not Resistance Valid.
• If the classification status is overcurrent, class mismatch, or unknown.

Figure 36. Automatic 4-Port Operation Schematic