High Power PD Controllers with Built-In Switchers Address IEEE 802.3at PoE+ Standard

(Product News, 2 Jul 2009)

Linear Technology Corp. introduces the LTC4269-1, LTC4269-2 and LTC4278, IEEE 802.3at compliant Power over Ethernet (PoE+) interface controllers with integrated switching regulators for high-power Powered Device (PD) applications up to 25.5W and beyond. The new IEEE 802.3at definition, also known as the PoE+ standard, simultaneously expands the power budget and improves the classification mechanism used by Power Sourcing Equipment (PSE) and PDs to identify each other. The LTC4269 and LTC4278 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.

The LTC4269 and LTC4278 cater to a new breed of applications utilizing the new PoE+ standard, including video conferencing stations, RFID readers, pan-tilt-zoom security cameras and long range wireless access points. The LTC4269 and LTC4278 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, allocating 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.

The LTC4269 and LTC4278 offer enhancements to the conventional PoE features. For efficient power allocation, 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. The LTC4269 and LTC4278 also include complementary power good outputs, an onboard signature resistor, undervoltage lockout, soft-start ramping and comprehensive thermal protection.

The LTC4269-1 and LTC4278 integrate a synchronous flyback controller that features Linear's patented No-Opto feedback topology to provide full IEEE 802.3 isolation. In addition, 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% efficiency. All versions are offered in commercial and industrial grades, supporting operating temperature ranges from 0°C to 70°C and -40°C to 85°C, respectively, and are available in a compact, RoHS-compliant, 7mm x 4mm 32-pin DFN package.