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PD controllers address PoE+ standard

Posted: 03 Jul 2009 ?? ?Print Version ?Bookmark and Share

Keywords:interface? controller? power sourcing equipment? PoE+?

From Linear Technology Corp. come interface controllers with integrated switching regulators for high-power powered device (PD) applications up to 25.5W and beyond. The LTC4269-1, LTC4269-2 and LTC4278 are IEEE 802.3at (PoE+) compliant.

The new IEEE 802.3at standard, popularly known as PoE+, expands the power budget and improves the classification mechanism used by power sourcing equipment (PSE) and PDs to identify each other. The new interface controllers support 2-event classification, are backward compatible with IEEE 802.3af devices, and open up the next level of PoE applications. These devices integrate both the PD controller and either a synchronous flyback controller (LTC4269-1 and LTC4278) or synchronous forward controller (LTC4269-2) for a complete IEEE 802.3at PD control solution.

They are recommended for video conferencing stations, RFID readers, pan-tilt-zoom security cameras and long range wireless access points. They distinguish PSEs and PDs as either Type 1 hardware, complying with IEEE 802.3af power levels, or Type 2 hardware, complying with IEEE 802.3at power levels, and allocate power accordingly. 2-event hardware classification allows a Type 2 PSE to identify connection to a Type 2 PD and signals the PD that it can source the higher power levels associated with 802.3at power. This new classification mechanism ensures interoperability between Type 1 and Type 2 devices.

For efficient power allocation with the LTC4269 and LTC4278, users can configure a classification load current that represents the PD power classification. A shutdown pin with signature corrupt provides flexible auxiliary power supply support. A rugged 100V Hot Swap MOSFET isolates the PoE interface controller and DC/DC converter during detection and classification, while providing 100mA of inrush current for smooth power-up transitions with any PSE. They also include complementary power good outputs, an onboard signature resistor, undervoltage lockout, soft-start ramping and comprehensive thermal protection.

Linear's patented No-Opto feedback topology is featured in a synchronous flyback controller that is integrated into the LTC4269-1 and LTC4278 to provide full IEEE 802.3 isolation. Also, the LTC4278 accommodates 10V to 57V auxiliary power to provide the ultimate in power sourcing options. The LTC4269-2 integrates a synchronous forward controller that boasts greater than 94 percent efficiency.

All versions are offered in commercial and industrial grades, supporting operating temperature ranges from 0C to 70C and -40C to 85C, respectively, and are available in a compact, RoHS-compliant, 7mm x 4mm 32-pin DFN package.

The LTC4269 and LTC4278 provide an upgrade path from Linear's existing PD products, including the IEEE 802.3af pin-compatible LTC4268-1 and are supported by Linear's deep technical expertise in PoE circuit design, ensuring a smooth transition to the new PoE+ standard.

The LTC4269-1 is priced starting at $2.40 each, and the LTC4269-2 and LTC4278 are priced starting at $2.60 each in 1,000-piece quantities.

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