PRODUCTS & TECHNOLOGY
High Efficiency Power over Ethernet Controllers Provide up to 90W Delivered Power
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For devices requiring power over Ethernet (PoE), PoE+ limits the maximum power delivery (PD) 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. Now the LT4275, LTPoE++ from Linear Technology 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++ 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. For efficient power allocation, PD users can configure a classification that represents the PD power usage. A 100V abs max rated input voltage means the LT4275 easily survives and protects PDs from the most common Ethernet line surges. A programmable auxiliary power pin with signature corrupt provides support down to 9V. The LT4275 also includes a power good output, onboard signature resistor, undervoltage lockout and comprehensive thermal protection.
Linear Technology, Milpitas, CA. (408) 432-1900. [www.linear.com].