Power over Ethernet (PoE) technology has succeeded in a variety of applications such as remotely powered network switches and access points. But many devices such as pan-tilt-zoom cameras or access points connected via long cable runs require more power than the 12.95W defined in the original IEEE 802.3af standard. With the LTC4265 PoE controller, Linear Technology addresses such high-power applications with a second-generation design that meets the newer 802.3at standard also referred to as PoE+. The controller supports Powered Device (PD) applications that consume up to 25.5W of power and also includes a classification mechanism for communication with Power Sourcing Equipment (PSE).
The controller offers 2-event classification recognition that is backwards compatible with the original PoE specification. The IC recognizes a PSE as either Type-1 or Type-2 and allocates power accordingly. Users can configure a classification load that represents the PD power classification. The design also supports auxiliary power supplies through an integrated shutdown pin.
The LTC4265 integrates a 100V MOSFET to isolate the controller and external DC/DC converter during detection and classification. The MOSFET limits inrush current to 100mA. The IC also includes a signature resistor, comprehensive thermal protection, and undervoltage and overvoltage lockout. The DFN-12-packaged IC is available in commercial and industrial versions and starts at $1.40 (1000). The data sheet provides additional specs.