Electronic Design

Network Power Controller Ensures Safe Insertion Of IP Phones

Hoping to get an edge in upcoming IP phones and DTE power-distribution systems, Linear Technology Corp. has readied a −48-V network power controller. The LT4255 quad controller enables the safe insertion and removal of IP phones into and from the Ethernet.

One unit can control 48 V to four IP phone lines. Each line is turned on and off via software control. The LT4255 also provides short-circuit protection, open-circuit detection, and "power good" indication for each line. To cut power dissipation in the switch during shorts and startup, current foldback is included.

External switches and current-sense resistors permit scaling of current, voltage, and power-dissipation levels. They protect against voltage and current spikes as well. Also, the LT4255 controls external n-channel MOSFETs in the −48-V power path and limits inrush current.

Other features include four independent relay drivers and a two-wire serial interface. Using a 5-bit programmable digital address, this interface lets designers control up to 128 channels via two digital lines. To avoid continuous software polling for fault detection, the controller uses a fault output signal to generate an interrupt condition.

The LT4255 is designed to comply with IEEE 802.3af. This standard, now a working draft, is expected to be adopted early next year. Implemented in biCMOS, the LT4255 will go into production next month. It's housed in a 28-pin SSOP plastic package and screened to both commercial and industrial temperature ranges. Contact Linear for pricing information.

Linear Technology Corp., 1630 McCarthy Blvd., Milpitas, CA 95035-7417; (408) 432-1900; fax (408) 434-6441; www.linear-tech.com.

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