IEEE 802.3bt, PoE, higher-power PD controller

IEEE 802.3bt, PoE, higher-power PD controller

New Products |
By Graham Prophet

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).


Linear Technology;


next page; feature summary

Summary of features: LT4295


IEEE 802.3af/at/bt (Draft 2.0) Powered Device (PD) with forward/flyback controller

External hot swap N-channel MOSFET for lowest power dissipation & highest system efficiency

Supports up to 71W PDs

5-event classification sensing

Superior surge protection (100V absolute maximum)

Wide junction temperature range (–40°C to 125°C)

>94% end-to-end efficiency with LT4321 ideal bridge

No-opto flyback operation

Auxiliary power support as low as 9V

Available in 28-lead 4 x 5mm QFN package



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