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POE controller gears up for new physical layer
By Margery Conner, Technical Editor -- EDN, 3/21/2008
Anticipating the new 802.3at version of POE (power over Ethernet), Akros Silicon has introduced its AS1135 PD (powered-device)-controller IC, which the company claims is the first IC to implement the two-event PHY (physical-layer) classification of the IEEE 802.3at standard Draft 2.0. The new version of the standard raises the maximum available PD-controller-input power to 30W from the 13W that the 802.3af standard specifies. Some PDs currently offer 30W of power, but use the handshake mechanism that the current standard specifies. According to Amit Gattani, director of marketing for Akros, the draft version of the 802.3at standard states that an older device that cannot conform with the new classification scheme, relying instead on the older handshake sequence, receives only 13W of power, rather than 30W.
While the new 802.3at standard is under development, the IEEE standards body has finalized the PHY classification, which allows PDs and PSE (power-sourcing equipment) to recognize each other as 802.3at-compliant. To implement the classification, the AS1135 provides the 802.3at-detection function on a logic-output pin, indicating successful POE connection to Type 2 PSE. The AS1135 can also operate with local-power input as low as 10V, so PDs and PSE devices integrating the AS1135 automatically adapt to legacy Ethernet and 30W 802.3at POE networks.
Ethernet systems are moving outside the more benign office or factory environment into regions such as China and India, which may have less stable power quality and in which lightning surges and noise can interfere with power and signal quality. As it did with its first POE product, the AS16XX, Akros continues with the AS1135 to emphasize on-chip EMI (electromagnetic-interference) filtering and surge suppression: The chip meets the IEC (International Electrotechnical Commission) 61000-4-2/3/4/5/6 and IEC 60950 requirements for surge protection, EMI filtering, and isolation. The chip is available in a 20-pin, 5×5-mm QFN with a ROHS (restriction of hazardous-substances)-compliant package and sells for $1.66 (1000).
