PoE - PD controller

Amina,

A "PD-only" controller is less integrated than a "PD controller plus DC/DC converter."

The PD-only controller (example: TPS2378) provides the system with a way to complete core PoE functions (detection and classification of a load) through communication with the PSE.  However, it requires coupling with a DC/DC PWM solution - such as the LM5116 or UCC2897A - for the power stage.

PD controllers which integrate the DC/DC converter (examples:  TPS23751, TPS23754) can enable smaller form factor PCBs (1 less part) and, in some cases, a lower overall system cost than the 2-chip approach.

With that said, selecting a PD-only controller enables greater flexibility across a platform of models - say, one model where cost is the #1 objective (and can partner with a flyback PWM) and one that cares more about efficiency (and can partner with an active bridge PWM).  In this business model, one PD-only controller can be qualified (such as the TPS2378) and used across multiple platforms.

TI offers both options in order to deliver a flexible suite of PoE options.

Thank you for your interest in TI PoE solutions!