Linear Technology Corporation has introduced 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 25.5 W 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 100 V Hot Swap MOSFET isolates the PoE interface controller and DC/DC converter during detection and classification, while providing 100 mA 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 10 V to 57 V 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 0 to 70 degrees C and -40 to 85 degrees C, respectively, and are available in a compact, RoHS-compliant, 7 mm x 4 mm 32-pin DFN package.
Availability and Pricing
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. 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 technical expertise in PoE circuit design, ensuring a smooth transition to the new PoE+ standard.
Related links:
LTC4269-1
PoE samples and demo boards
