Milpitas, Calif. - Linear Technology's LTC4257 interface controller is the company's first power-over-Ethernet device made specifically to meet the powered device (PD) requirements of IEEE's 802.3af specification.
The hot-swap, high-volt CMOS device, working from a -48-V source (delivered by the power-sourcing equipment, PSE), is a 100-V-rated power switch that connects the PSE source to loads such as voice-over-Internet Protocol phones and wireless-access points when the input voltage reaches a valid level.
It includes a precision 25-kohm "signature" resistance to identify itself as a PD, inrush current limiting, thermal limiting for fault protection and circuitry that lets the user classify the current source (power classes 1 to 4) using an external resistor.
The interface controller's inrush current-limiting feature keeps line current below 400 mA. An open-drain power-good output signals that the voltage drop across the internal power MOSFET has dropped below 1.5 V, indicating that the output has reached its final value and it is safe to turn on the system load. The LTC4257, in an SO-8 package, is priced at $1.65 each in 1,000-piece quantities.
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