SLVSF02D March 2019 – May 2020 TPS23881
The IEEE 802.3at-2009 standard previously expanded PoE power delivery from 15.4W (Commonly referred to as .af or Type-1 PoE) to 30 W (.at or Type-2 PoE) of sourced power from the PSE (Power Sourcing Equipment) over 2-pairs of ethernet wires (Commonly known as either the Alt-A or Alt-B pair sets). The IEEE 802.3bt standard further expands power delivery up to 90 W sourced from a PSE by allowing for power delivery over both the ALT-A and ALT-B pairsets in parallel. Two new PoE equipment "Types" have also been created as part of the new standard. Type 3 PSE equipment will be capable of sourcing up to 60 W of power over 4-pair or 30 W over 2-pair while supporting the new MPS requirements. Type 4 PSE equipment will be capable of sourcing up to 90 W of power over 4-pair. The TPS23881 has been designed to be fully configurable to support any of these configurations.
The Maintain Power Signature (or MPS) requirements have also been updated for the new standard. The previous version of the standard only required PSEs to maintain power on a port if the PD (Powered Device) current exceeded 10 mA for at least 60 ms every 300 ms to 400 ms. By decreasing these requirements to 6 ms every 320 ms to 400 ms, the minimum power requirement to maintain PoE power have been reduced by a factor of nearly 10.