Nye controller baner vej for IEEE 802.3at PoE+
Linear Technology lancerer LTC4266, der er en 4-port Power over Ethernet (PoE) controller til IEEE 802.3at (25.5W) applikationer (in english).
Linear Technology Corp. introduces the LTC4266, a 4-port Power over Ethernet (PoE) controller for Power Sourcing Equipment (PSE) required to provide IEEE 802.3at (25.5W) or proprietary higher power levels.
Next-generation PoE applications call for more power to support demanding features, while increasing power efficiency in an effort to be more 'green' and reduce costs. The LTC4266 provides up to 100W over 4-pair Ethernet cabling and is fully compliant with the new IEEE 802.3at PoE+ standard and backward compatible with the prior IEEE 802.3af PoE standard.
To help conserve power, the LTC4266 delivers the lowest-in-industry heat dissipation by using low RDS(ON) MOSFETs and 0.25Ohm sense resistors, eliminating the need for expensive heat sinks and providing a more robust PSE solution.
The LTC4266 is suitable for a wide variety of PSE applications, including
next-generation switches, routers, hubs and midspans. Users will appreciate the extremely low power dissipation which makes thermal design significantly easier than when designing with PSEs that integrate more fragile, normally higher RDS(ON), MOSFETs.
Up to four independent PSE channels are available. IEEE 802.3at powered devices (PDs) can request up to 25.5W of power by responding to 2-event classification from the LTC4266, confirming that the PD is indeed a high power device. PD discovery is accomplished using a proprietary dual-mode, four point detection mechanism that ensures the best immunity from false PD detection.
Advanced power management also includes prioritized fast shutdown, 14.5-bit per-port voltage and current readback, 8-bit programmable current limits and 7-bit programmable overload current limits. A 1MHz I2C interface allows a host controller to digitally configure the IC or query port readings.
The LTC4266 is offered in commercial and industrial temperature grades, and is available in RoHS-compliant 5mm x 7mm QFN-38 or SSOP-36 packages. The LTC4266 is priced starting at $6.95 each in 1,000 piece quantities and is available today in production quantities.
The LTC4266 provides an upgrade path from Linear’s existing PSE controllers, including the IEEE 802.3af pin-compatible LTC4258 or LTC4259A, and is supported with years of technical experience in PoE circuit design for a smooth transition to the new PoE+ standard.
<b>Background on PoE and PoE+</b>
Power over Ethernet was defined by the IEEE 802.3af task force in 2003 and has enjoyed wide industry acceptance. This standard defined nominal power delivery at 12.95W, which was adequate for early adopter applications, such as basic VoIP phones, security cameras and wireless access points.
However, today’s applications requiring more power to support higher performance include full-featured video phones, videoconferencing stations and pan-tilt-zoom cameras. To address this need, the IEEE 802.3at task force was born in 2005 and is currently defining the new PoE+ standard, set to finalize toward the end of summer 2009.
The PoE+ standard differs from the PoE standard in two major ways. First, it increases the minimum power being delivered to a PD from 12.95W to 25.5W. Second, the classification mechanism used to allow Power Sourcing Equipment (PSE) and PDs to mutually identify each other has been changed to allow for interoperability between both PSEs and PDs across both standards.
The increased power rating may be straightforward, but there is a need for clarification of the new 2-event hardware classification, which involves the PSE essentially repeating the 802.3af voltage probe twice. In addition, PSEs can classify the PD over the data layer using LLDP (link layer discovery protocol), which is transparent to the PSE controller, but is a new, optional means of power classification and allocation. Using LLDP, PSEs and PDs can negotiate power to within 0.1W.
