Interface Controller simplifies powered device design.
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Press Release Summary:
Model LTC4257 Power over Ethernet Interface Controller incorporates circuitry necessary to connect powered device to IEEE 802.3af powered Ethernet network. Offered in SO-8 package, -48V powered unit incorporates 25 k signature resistance, programmable classification, power switching, inrush current limiting, and fault protection. Integrated 100 V power MOSFET keeps PD circuitry disconnected from Ethernet cable until input voltage reaches valid level.
Original Press Release:
Power over Ethernet Interface Controller Simplifies Powered Device Design for IEEE 802.3af Applications
MILPITAS, CA - June 30, 2003 - Building on its industry-leading Hot SwapTM technology, Linear Technology Corporation introduces the LTC4257 Power over Ethernet Interface Controller, incorporating virtually all the circuitry necessary to connect a powered device to an IEEE 802.3af powered Ethernet network. This -48V powered interface controller greatly simplifies powered device design by incorporating the signature resistance, programmable classification, power switching, inrush current limiting, and fault protection. The LTC4257 can interface directly with a variety of Linear Technology DC/DC converter products to provide a cost effective power solution for IP phones, wireless access points and other powered devices (PDs).
The LTC4257's integrated 100V power MOSFET keeps the PD circuitry disconnected from the Ethernet cable until the input voltage reaches a valid level. Inrush current limiting keeps the line current below 400mA and thermal limiting protects the circuit from extreme fault conditions. The LTC4257 also includes an integrated precision 25k signature resistance to properly identify the PD and a classification signature circuit that can be set with a single external resistor to support power classes 0 through 4. An open-drain Power Good output signals that the voltage drop across the internal power MOSFET has dropped below 1.5V, indicating that the output has reached its final value and it is safe to turn on the system.
The LTC4257 has applications in PDs for digital voice-over-IP phones, network wireless access points, PDA charging stations, HVAC thermostats, or any small Ethernet-connected device that requires less than 13W. A PD need not use the data link at all; something as simple as a cell phone battery charger or an illuminated exit sign could draw its power from an Ethernet connection.
The LTC4257 is designed to satisfy the specific demands of the emerging IEEE 802.3af standard for powered devices, allowing designers to focus on overall system design. The LTC4257 is offered in the SO-8 package. Pricing starts at $1.65 each for 1,000 piece quantities.
Summary of Features: LTC4257
Complete Power Interface Port for Powered Devices (PDs) Implementing the IEEE 802.3 standard, Clause 33 (Currently in Draft under IEEE 802.3af)
Onboard 100V, 400mA Power MOSFET
Precision Inrush Current Limit
Onboard 25k Signature Resistor
Programmable Classification Current (Class 1-4)
Supports Measured Current and Measured Voltage Classification Methods
Undervoltage Lockout
Smart Thermal Protection
Power Good Signal
Available in 8-Pin SO Package
Company Background
Linear Technology Corporation was founded in 1981 as a manufacturer of high performance linear integrated circuits. Linear Technology products include operational, instrumentation and audio amplifiers; voltage regulators, power management devices, DC-DC converters and voltage references; comparators; monolithic filters; communications interface circuits; one-chip data acquisition sub-systems; pulse-width modulators and sample-and-hold devices; and high frequency devices. Applications for Linear Technology's high performance circuits include wireless and broadband telecommunications infrastructure, cellular telephones, networking products and satellite systems, notebook and desk top computers, computer peripherals, video/multimedia, industrial and medical instrumentation, automotive electronics, factory automation, process control, military and space systems, and high-end consumer products including digital cameras, MP3 players and other electronic products.
