Quad power over ethernet controller
LINEAR Technology has released two quad power over ethernet controllers that are compliant with the IEEE 802.3af specification. They are available from Soanar .
The controllers provide autonomous operation for power sourcing equipment, sequencing through all of the required tasks without processor intervention. They can operate in either automatic stand alone or processor-controlled modes. The LTC4258 implements 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 quad configuration in the 36-pin SSOP package is optimised 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 utilise high voltage technology operating on -48V while the complex logic and interface use the 3.3V supply.
25-Feb-2004