PoE controller integrates power interface port

National Semiconductor Corp. introduced its single-chip power-over-Ethernet (PoE) controller for higher-power PoE applications. The LM5072 integrates a programmable power interface port and a pulse-width modulation (PWM) controller.

The product comes with programmable current limiting that allows it to draw up to 25W from a PoE-enabled port. For standard 802.3af powered devices (PDs), the current may be programmed to any value between 150mA and 800mA, or the programming resistor can be disconnected to switch the LM5072 to the default mode with 440mA maximum current draw. The LM5072, which has maximum input voltage and current ratings of 100V and 800mA, also supports applications that accept power from auxiliary sources.

Applications for the LM5072 include VoIP phones, remote security cameras, card readers, wireless access points, computer telephony, PDs in PoE systems and 48V telecom power supply controls.

The device's PoE port input and internal PD interface MOSFET are specified to an absolute maximum voltage of 100V. Designers can set the port current limit to the default 802.3af level or program it from 100mA to 800mA. The in-rush current limit defaults to 150mA, but can be programmed over the same range as the port current limit. The precision 25 k? signature detection resistor is also integrated within the LM5072. Its fully configurable AC adapter interface allows designers to connect auxiliary power to either the front-end PoE port or rear DC/DC converter. With a rear auxiliary supply, the LM5072 can disable the PoE interface to reduce power drawn from power sourcing equipment when auxiliary power is applied.

The LM5072's PWM controller includes a high-voltage bias regulator, programmable soft-start and programmable switching frequency with clock synchronization capability. The product is available with either 50 percent or 80 percent maximum PWM duty cycle, which is said to allow the controller to support a variety of DC/DC converter topologies and operation. The LM5072 includes a two-percent-accurate voltage reference and error amplifier for direct control of the output in non-isolated DC/DC applications.

The LM5072 is offered in the thermally enhanced 16-pin TSSOP-EP package.