Monday, November 16, 2009

Linear Introduces Four-Port PoE Controller

Linear Technology has unveiled the LTC4266 four-port power-over-Ethernet (PoE) controller for power sourcing equipment (PSE) needed 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 environmentally friendly and to reduce costs, according to the company.

The LTC4266 provides up to 100W over four-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 low heat dissipation by using low RDS(ON) MOSFETs and 0.25ohm sense resistors, eliminating the need for expensive heatsinks and providing a stronger PSE solution. The LTC4266 is suitable for a variety of PSE applications, including next-generation switches, routers, hubs and midspans.

The low power dissipation is claimed to make thermal design 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 two-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 prioritised fast shutdown, 14.5-bit per-port voltage and current read-back, eight-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 5 x 7mm QFN-38 or SSOP-36 packages. Priced from USD6.95 (GBP4.20) each in 1,000-piece quantities, it is available now 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.

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