The LT4275 is a pin-for-pin compatible family of IEEE 802.3 and LTPoE++ powered device (PD) controllers. The LT4275A employs a proprietary LTPoE++ classification scheme, delivering 38.7W, 52.7W, 70W or 90W of power at the PD RJ45 connector and is fully compatible with IEEE 802.3. The LT4275B is an IEEE 802.3at compliant, Type 2 (PoE+) PD delivering up to 25.5W while the LT4275C is an IEEE 802.3af compliant, Type 1 (PoE) PD delivering up to 13W.

The LT4275 family of controllers from Linear Technology are LTPoE++, PoE+ and PoE-compliant powered device (PD) interface controllers 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. 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.

The LT4275 is offered in industrial and automotive grades, supporting operating temperature ranges from -40°C to 85°C and -40°C to 125°C, respectively, and is available in small RoHS-compliant 10-pin MSOP or 3mm x 3mm DFN packages. The LT4275 is priced starting at $1.45 each in 1,000-piece quantities and is available in production quantities.

The LT4275 provides an upgrade path from Linear Technology’s existing PD products, including the LTC4265 PoE+ PD controller, and seamlessly connects to any of Linear Technology’s latest PSE controllers, including the single-port LTC4274, 4-port LTC4266 and 12-port LTC4270/71 chipset.

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For more information on the LT4275, visit .

Summary of Features of the LT4275:

  • IEEE 802.3af/at & LTPoE++ Powered Device (PD) Controller
  • LTPoE++ Supports Power Levels up to 90W
  • LT4275A Supports All of the Following Standards:
  • LTPoE++ 38.7W, 52.7W, 70W & 90W
  • IEEE 802.3at 25.5W Compliant
  • IEEE 802.3af up to 13W Compliant
  • LT4275B is IEEE 802.3at/af Compliant
  • LT4275C is IEEE 802.3af Compliant
  • 100V Absolute Maximum Input Voltage
  • Integrated Signature Resistor
  • External Hot Swap N-channel MOSFET for Lowest Power Dissipation & Highest System Efficiency
  • Programmable Aux Power Support as Low as 9V
  • Available in 10-Pin MSOP & 3mm x 3mm DFN Packages

Typical Application


  • High Power Wireless Data Systems
  • Outdoor Security Camera Equipment
  • Commercial and Public Information Displays
  • High Temperature Industrial Applications

About Linear Technology

Linear Technology Corporation, a manufacturer of high performance linear integrated circuits, was founded in 1981, became a public company in 1986 and joined the S&P 500 index of major public companies in 2000. Linear Technology products include high performance amplifiers, comparators, voltage references, monolithic filters, linear regulators, DC-DC converters, battery chargers, data converters, communications interface circuits, RF signal conditioning circuits, µModule products, and many other analog functions.  Applications for Linear Technology’s high performance circuits include telecommunications, cellular telephones, networking products such as optical switches, notebook and desktop computers, computer peripherals, video/multimedia, industrial instrumentation, security monitoring devices, high-end consumer products such as digital cameras and MP3 players, complex medical devices, automotive electronics, factory automation, process control, and military and space systems.

Linear Technology (UK) Limited
Tel: +44 (0)1628 477066

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