Linear Tech High Efficiency PSE Controller Addresses New IEEE 802.3at PoE+ Standard
Linear Technology Corp. introduced the LTC4274, a single-channel 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 LTC4274 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 LTC4274 delivers the lowest-in-industry heat dissipation by using low RDS(ON) MOSFETs and 0.25Ω sense resistors, eliminating the need for expensive heat sinks and providing a more robust PSE solution.
The LTC4274 is suitable for a wide variety of PSE applications, including next-generation single-port switches, cameras and electronic message boards. Users will appreciate the extremely low power dissipation of the LTC4274, which makes thermal design significantly easier than designing with PSEs that integrate more fragile, normally higher RDS(ON), MOSFETs. IEEE 802.3at powered devices (PDs) can request up to 25.5W of power, responding to 2-event classification from the LTC4274 and confirming that the PD is indeed a high power device. PD discovery is accomplished using a proprietary dual-mode, 4-point detection mechanism that ensures the best immunity from false detection.
Advanced power management also includes prioritized fast shutdown, 14.5-bit 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 LTC4274 is offered in commercial and industrial temperature grades, and is available in a RoHS-compliant 5 x 7mm QFN-38 package. The LTC4274 is priced starting at $4.95 each in 1,000 piece quantities and is available today in production quantities. The LTC4274 provides an upgrade path from the IEEE 802.3af compliant LTC4263/-1, and is supported with years of technical experience in PoE circuit design for a smooth transition to the new PoE+ standard.
