Another company has joined PowerDsine in introducing a Power-Over-Ethernet
(PoE) controller that anticipates the higher power capabilities addressed by
the IEEE 802.3at PoE Plus task force. While PoE Plus is still very much a work
in progress, Texas Instruments has introduced a 26-W powered-device (PD) controller.
TI's eight-pin TPS2376-H lets designers implement a non-standard PD that draws
up to 26 W from power-source equipment (PSE) with a minimum of 52 V of input
and over 100 m of CAT-5 Ethernet cable. It supports PowerDsine's preferred approach
for high power: using both the data pairs and the spare pairs in the CAT-5 cable
(see the figure). The alternative under discussion
by the task force is simply to increase the current limits in the current 802.3af
standard.
One of the issues taking up much of the task force's time is classification:
how the PD tells the PSE at the Ethernet switch or bridge how much power it
needs. The PSE uses this information for power-supply load balancing and fault
detection. But until the task force resolves some basic classification issues
(10 classes were under consideration at the September meeting; basic 803.2af
provides for four), classifying high-power PDs is ad hoc.
The TI datasheet says simply, "A high power system will not meet the standard
power CLASS ranges defined in IEEE 802.3af... An end-to-end high power system
may either redefine the CLASS power, or dispense with CLASS entirely."
The TPS2376-H comes in an eight-pin, SOIC PowerPad package with an integrated
0.6-ΩFET to minimize heat dissipation in the system. Pricing is $1.25 each
in lots of 1000.
Texas Instruments
www.ti.com
