AN313

AN313 USING THE Si3400 AND Si3401 IN HIGH POWER APPLICATIONS 1. Introduction Emerging Power over Ethernet (PoE) applications, such as multi-band and 802.11n access points, often require more power than the 12.95 W specified by the IEEE 802.3af. This application note outlines how to use the Si3400 and Si3401 to support powered device (PD) applications over 15 W output, which corresponds to www.DataSheet4U.com about 20 W of input power from the PSE. The current standard for Power over Ethernet or PoE is IEEE Std™ 802.3-2005, clause 33. Although there is currently no ratified standard beyond this, a standard, commonly referred to as PoE+, is being actively developed in the p802.3at subcommittee. While this note attempts to be consistent with the general direction in discussion by the p802.3at committee, it should be emphasized that no standard currently exists to support power above the current specification's 12.95 W maximum of power available at the PD. The proposed solutions in this document are intended to serve as practical solutions for higher power PDs before p802.3at is ratified. Based on current discussions in the p802.3at committee, it appears likely that the minimum PSE output voltage will be increased, and the maximum cable resistance will be decreased to support PoE Plus. It is also likely that there will be a provision for classifying at the current maximum supported power of 12.95 W input and then negotiating with the PSE for higher power via a simple data e...