AN296 Datasheet, PDF (1/24 Pages) Silicon Laboratories – USING THE Si3400 AND Si3401 POE PD CONTROLLERS IN ISOLATED AND NON-ISOLATED DESIGNS

AN296
USING THE Si3400 AND Si3401 POE PD CONTROLLERS
IN ISOLATED AND NON-ISOLATED DESIGNS
1. Introduction
Power over Ethernet (PoE) is an IEEE standard (IEEE 802.3af) for delivering power through Ethernet cables.
802.3af specifies two options for this as shown in Figures 1 and 2.
The option shown in Figure 1 must be used for "midspan equipment", which injects power on the Ethernet
connection of an existing Ethernet link. Endpoint equipment, such as an Ethernet switch, can use either option.
POWER SOURCING
EQUIPMENT (PSE)
POWERED DEVICE
(PD)
+
TX
_
48 V
RX
4
4
5
5
SPARE PAIR
1
1
2
2
SIGNAL PAIR
3
3
6
6
SIGNAL PAIR
7
7
RX
DC/DC
Converter
TX
8
8
SPARE PAIR
Figure 1. Power Delivered over Spare Pair
POWER SOURCING
EQUIPMENT (PSE)
POWERED DEVICE
(PD)
4
4
±
TX
48 V ^± _RX
5
5
SPARE PAIR
1
1
2
2
SIGNAL PAIR
3
3
6
6
SIGNAL PAIR
7
7
RX
DC/DC
Converter
TX
8
8
SPARE PAIR
Figure 2. Power Delivered over Signal Pair
Rev. 0.8 8/07
Copyright © 2007 by Silicon Laboratories
AN296