Single-chip Power over Ethernet (PoE) solutions recently began gaining momentum in such applications as wireless LANs and Voice over Internet Protocol (VoIP), mainly because they offer simplicity and cost savings.
The new breed of chips — manufactured and marketed by such companies as Freescale Semiconductor, National Semiconductor and Texas Instruments — serve as controllers for situations in which up to 13-26W of power is carried over Ethernet cabling.
“With Power over Ethernet, you don’t need the ac wall adaptor at your desk,” notes Jan Krellner, applications systems engineer for PoE products at Freescale. “Also, you have less wiring hassles. Everywhere you have Ethernet, you can connect to the cable without worrying about power.”
To date, applications for PoE have included IP phones, IP cameras, laptop computers, wireless access points, networked kiosk terminals, security video cameras, emergency lighting controls, MP3 players and PDA chargers. Chip makers expect to uncover more applications, however, as the technology grows in popularity. Here are three examples of single-chip PoE technology introduced during 2006.
TI’s 26W PoE for cameras, phones
Texas Instruments’ eight-pin, TPS2376-H controller contains the features needed to develop an IEEE 802.3af-compliant powered device. It incorporates such safety features as a programmable, 600-mA current limit with thermal shutdown, auto-retry and fault protection. The high-power device also allows a designer to implement a non-standard powered device that draws up to 26W of power from power source equipment (PSE) with a minimum of 52V of input and over 100m of CAT-5 Ethernet cable.
Flexible single-chip PoE
Freescale Semiconductor’s MCZ34670, introduced in October, combines a powered device interface and a pulsewidth modulator controller. Designed to support the IEEE 802.3af PoE standard, the new device offers a high level of integration that enables developers to design cost-effective Ethernet-powered end devices with minimal external components. With the new product, Freescale hopes to go beyond such accepted PoE applications as VoIP and wireless LANs, and create a new niche in such applications as RFID tags and network security cameras.
High-power PoE controller
National Semiconductor engineers designed the LM5072 with programmable current limiting that allows it to draw up to 25W from a PoE-enabled port, since many emerging PoE applications require power that exceeds the limit of the existing standard. For standard 802.3af Powered Devices (PDs), the current may also be programmed to any value between 150 and 800 mA, or the programming resistor can be simply disconnected to switch the LM5072 to the default mode with 440 mA maximum current draw.
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