The LT4275 is a LTPoE++, PoE+ and PoE-compliant powered device (PD) interface controller for applications requiring up to 90W of delivered power. PoE+ limits the maximum PD power delivery to 25.5W, which is insufficient to power today's new class of power-hungry applications, such as picocells, base stations, signage and heated outdoor cameras. Linear Technology's LTPoE++ standard addresses this market by expanding the power budget to four different power levels 38.7W, 52.7W, 70W and 90W enabling complete high power LTPoE++ systems. The LTPoE++ standard employs a classification scheme that simply enables LTPoE++ power sourcing equipment (PSE) controllers and LTPoE++ PD controllers to reliably communicate with one another while maintaining interoperability with IEEE standard equipment. The LT4275A (LTPoE++), LT4275B (PoE+) and LT4275C (PoE) efficiently deliver power to PD loads using just one IC.Unlike traditional PD controllers that integrate the power MOSFET, the LT4275 controls an external MOSFET to drastically reduce overall PD heat dissipation and maximize power efficiency, especially important at higher power levels. This novel approach allows users to size the MOSFET to their application's specific heating and efficiency requirements, enabling the use of low RDS(ON) 30mOhm MOSFETs if necessary. The LT4275 recognizes a PSE as either Type 1 hardware complying with the IEEE 802.3af 13W power level, Type 2 hardware, complying with IEEE 802.3at 25.5W power level or LTPoE++ hardware complying with 38.7W to 90W power levels, and passes power accordingly. The LT4275 is offered in industrial and automotive grades supporting operating temp ranges from -40°C to 85°C and -40°C to 125°C. It is available in small 10-pin MSOP or 3mm x 3mm DFN packages and is priced starting at $1.45 each in 1,000-piece quantities.
