IEEE 802.3bt, PoE, higher-power PD controller
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; www.linear.com/product/LT4295
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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