Power controller targets power-over-Ethernet to 90W, drives external FET

July 27, 2015 // By Graham Prophet
Recently announced is the LT4276, a LTPoE++, PoE+ and PoE-compliant powered device (PD) interface controller (three variants) for applications requiring 2W to 90W of delivered power.

The LT4276 integrates a PD controller and an isolated switching regulator controller, capable of synchronous operation in both forward and flyback topologies with auxiliary power support. This integration simplifies front end PD designs by reducing component count and board space, allowing the LT4276A (LTPoE++), LT4276B (PoE+) and LT4276C (PoE) to efficiently deliver power to PD loads using a single IC.

Linear Technology’s LTPoE++ standard extends support for today’s class of very high power applications, such as picocell base stations, signage and heated outdoor security cameras, by expanding the power budget to four new power levels (38.7W, 52.7W, 70W and 90W). Unlike traditional PD controllers that integrate the power MOSFET, the LT4276 controls an external MOSFET to reduce overall PD heat dissipation and maximise power efficiency, especially important at higher power levels. This approach allows users to size the MOSFET to their application’s specific heating and efficiency requirements, enabling the use of MOSFETs with as low as 30 mΩ RDS(ON) where necessary. A 100V rated input voltage means the LT4276 survives and protects PDs from the most common Ethernet line surges.

The LT4276 is offered in industrial and extended temperature 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 28-lead 4 x 5 mm QFN packages. The LT4276 is priced starting at $2.25 (1000).

Linear notes that the device offers an upgrade path from existing PD products, including the LT4275 LTPoE++ PD controller, and connects to any of Linear Technology’s PSE controllers, including the single-port LTC4274, 4-port LTC4266, 8-port LTC4290/71 chipset and 12-port LTC4270/71 chipset. The LT4276 can also be used with the LT4321 ideal diode bridge controller to maximise available power and reduce heat dissipation in PDs.

Linear Technology; www.linear.com