Power Over Ethernet Controllers work autonomously.
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Press Release Summary:
Compliant with IEEE 802.3af specification, Models LTC4258/9 are quad PoE controllers that provide autonomous operation for power sourcing equipment, sequencing through required tasks without processor intervention. Model LTC4258 implements 802.3af detection and classification, current limiting for normal and fault operation, and DC disconnect detection. Model LTC4259 adds ability to implement AC disconnect detection. Both can communicate with host over 2-wire I2C bus.
Original Press Release:
Quad Power over Ethernet Controller Works Autonomously & Supports Both DC and AC Disconnect Sensing Methods
MILPITAS, CA - February 17, 2004 - Building on its industry leading Hot Swap(TM) controller technology, Linear Technology is shipping two quad Power over Ethernet (PoE) controllers that are fully compliant with the IEEE 802.3af specification. These controllers provide autonomous operation for Power Sourcing Equipment (PSE), sequencing through all of the required tasks without processor intervention. The devices can operate in either automatic standalone or processor-controlled modes. The LTC4258 implements the 802.3af detection and classification, current limiting for normal and fault operation and DC disconnect detection. The LTC4259 performs the same functions but also adds the ability to implement AC disconnect detection. Both devices can communicate with the host over the two-wire I2C bus, requiring minimal firmware support. The precision measurements for detection, classification and current sensing are performed by dedicated internal circuitry with fully specified accuracy.
The recently approved IEEE 802.3af Power over Ethernet specification defines a method to allow DC power to be delivered simultaneously over Ethernet networks. With about 13W of power available from the PSE, small data devices can be powered by their Ethernet connection, free from AC wall outlets. Such devices include digital Voice-over-IP phones, network wireless access points, PDA charging stations, print servers, HVAC thermostats, or any Ethernet-connected data device that would otherwise be powered by a wall transformer. The challenge is more than simply providing power to these new applications; there must also be safeguards to protect Ethernet ports in regular PCs and laptops from potentially destructive 48V common mode signal levels. The IEEE 802.3af specification requires several tightly defined impedance and current measurements to be made over the cable within strict time limitations. The critical element in assuring consistent interoperability is compliance to the IEEE 802.3af Power over Ethernet specification.
The quad configuration in the 36-pin SSOP package is optimized for board density in multi-channel systems. The only external components required are the external MOSFETs, sense resistors and passive components required for the chosen detection method. A dedicated microcontroller is not necessary. The power sections of the LTC4258/LTC4259 utilize high voltage technology operating on -48V while the complex logic and interface use the 3.3V supply.
The LTC4258 pricing starts at $6.35 each for 1,000 piece quantities and the LTC4259 pricing starts at $6.95 each for 1,000 piece quantities.
Summary of Features: LTC4258 & LTC4259
Controls Four Independent -48V Powered Ethernet Ports
Each Channel Includes:
- IEEE 802®.3af Compliant PD Detection and Classification
- Inrush Control
- Short-Circuit Protection with Current Foldback
- PD Disconnect Using AC or DC Sensing (LTC4259)
- PD Disconnect Using DC Sensing (LTC4258)
- Power Good Indication
Operates Autonomously or Controlled by I2C(TM) Serial Interface
4-Bit Programmable Digital Address Allows Control of up to 64 Channels
Programmable INT Pin Eliminates Software Polling
Current Limit Duty Cycle Protects External FETs
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.
