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Electronic Design

Protocols, PoE, And The Less-Is-More Objective

Three European developments give EEs frugal but flexible design opportunities.

Ericsson Power Modules has joined the Power Management Bus (PMBus) Implementers Forum. The company now can contribute to the development of a future, standardized digital power-management platform that it believes will benefit its customers in the short and long terms.

The PMBus open-standard digital power-management protocol facilitates communication with a power converter or other device by defining the transport and physical interface. It was created in October 2004 when Artesyn Technologies, Astec Power, and six major semiconductor manufacturers recognized that the lack of a suitable standard was inhibiting the adoption of an all-digital power-management solution. A total of 19 power sector companies are now on board.

STMicroelectronics has unveiled its compact class D power-amplifier (PA) chip. Designed for the latest mobile phones and similar products, the TS4962 offers higher audio power output while preserving and extending battery life (Fig. 1). It provides 3 W of output power into a 4-Ω loudspeaker when operating from a 5-V power supply. Also, it achieves 88% efficiency.

The TS4962's supply voltage ranges from 2.4 to 5.5 V. Its quiescent current with no input signal is 2.3 mA typical. Standby current is 10 nA when powered down using its active-low control line. Pop-and-click reduction circuitry provides low on/off switching noise while allowing the amplifier to start within 5 ms.

The gain is set using two external resistors. A fully differential design reduces RF rectification effects and eliminates the need for a bypass capacitor. Output power is 3 W into 4Ω or 1.75 W into 8Ω at 10% maximum total harmonic distortion plus noise (THD+N) on a 5-V supply. At 1% maximum THD+N, output power is 2.3 W into 4Ω on a 5-V supply or 0.75 W on a 3-V supply. Its signal-to-noise ratio is typically 85dB.

This small amplifier is available in a lead-free, 1.6-mm2 flip-chip package. It's supported by a development board, which includes the device pre-mounted onto a flip-chip to dual-inline package adapter for easier handling during evaluation.

According to National Semiconductor, its LM5071 is the industry's first single-chip, Power over Ethernet (PoE) device controller designed for low-voltage auxiliary power sources (Fig. 2). The company believes it will improve flexibility for operating PoE devices from ac adapters as low as 9.5 V or from the power-sourcing equipment

Devices powered by a PoE network include Internet Protocol phones, security cameras, and wireless local-area network (WLAN) nodes connected through Ethernet networking cables and ports. It's often necessary to operate these PoE devices from alternate power sources to relieve the burden on the power-sourcing equipment (PSE) or to operate them on a network that isn't PoE-enabled. Current solutions limit the choice of auxiliary power sources, which can drive up overall system cost or complexity.

The LM5071 also is the industry's first single-chip, IEEE 802.3af-compliant power-device (PD) interface port and pulse-width modulator (PWM) controller specifically designed to accept power from external ac adapters. Its integrated PD front end accepts power from the PSE or auxiliary power to a single chip with a dc-dc controller that steps down the input voltage to power various PD loads.

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