IEEE 802.3bt, PoE, higher-power PD controller

September 13, 2016 // By Graham Prophet
LT4295 is an IEEE 802.3bt powered device (PD) interface controller for applications requiring up to 71W of delivered power. The next Power over Ethernet (PoE) standard – IEEE 802.3bt – enables manufacturers to go beyond the 25.5W allocated by the 2009 IEEE 802.3at standard.

Linear Technology aims to be first to market with next-generation IEEE-compliant products. The new standard, also known as PoE++ or 4PPoE, increases the power budget to enable new applications and features, while supporting 10 Gigabit Ethernet (10GBASE-T) and maintaining backward compatibility with older IEEE equipment. The LT4295 is IEEE 802.3bt (Draft 2.0) compliant and supports newly introduced features, including all additional PD classes (5, 6, 7 and 8), additional PD types (Type 3 and Type 4), and 5-event classification.


The LT4295 is a single-signature 802.3bt PD controller that integrates an isolated switching regulator controller, capable of synchronous operation in both high efficiency forward and no-opto flyback topologies with auxiliary power support. This high level of integration simplifies front end PD designs by reducing component count and board space, allowing the LT4295 to efficiently deliver power to PD loads using just one IC. Unlike traditional PD controllers that integrate the power MOSFET, the LT4295 controls an external MOSFET to significantly reduce overall PD heat dissipation and maximize power efficiency, particularly important at 802.3bt’s higher power levels. An external MOSFET architecture allows users to size the MOSFET to their application’s requirements; standard LT4295-based implementations routinely select 30 mΩ RDS(ON) MOSFETs.


The LT4295 comes in industrial and automotive grades, supporting operating temperature ranges from –40°C to 85°C and –40°C to 125°C, respectively. It is priced from $2.75 (1,000).


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