The Si3400 and Si3401 Power over Ethernet (PoE) powered device (PD) controllers are designed in an efficient Silicon on Insulator (SOI) process technology, which enables the integration of a robust surge protection function. Competitive PoE PD devices require external transient voltage suppressors (TVS), such as an SMAJ58A, to provide surge protection. However, due to their inherently wider range of clamping voltage specifications, external TVS-based protectors typically necessitate the use of 100 V processes for the PD controller device. This note discusses some of the detailed considerations regarding the Si3400's proprietary surge protection circuitry that enable the Si3400 and Si3401 devices to yield robust and standards-compliant electrical surge immunity when used in Power over Ethernet powered device applications.