Power Over Ethernet Interoperability Guide

Allowed Port Voltage Sag under Current Limiting

Note that once current limiting occurs, the port voltage starts to fall suddenly. In that case, the AT standard specifically provides further relief. In Section 33.2.7.1 on page 46, the AT standard says:

A PSE….may remove power… when the PI voltage no longer meets the V_{PORT_PSE} specification.

V_{PORT_PSE} refers to Table 33-11, pages 45. This basically implies that if ever the port voltage falls below 44 V for Type 1 and 50 V for Type 2, the port can be turned off right away.

However, Table 33-11 along with Section 33.2.7.2 (page 46), demands a certain “glitch filtering” for Type 2 (only). Its basic purpose is to make the PSE more robust to withstand shorter, but more severe overload demands ...