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Audio amp reduces EMI, optimizes power

Santa Clara, Calif. — National Semiconductor Corp. says it has introduced the industry's first single-chip 3-W mono Class D audio amplifier with spread spectrum technology and an integrated boost converter. The LM48511 Boomer amplifier, part of National's PowerWise energy-efficient product portfolio, allows portable products to operate at a constant high-level output power even as batteries deplete to lower voltages.

The LM48511 high-efficiency Class D audio power amplifier provides 2.5 W to 3 W of continuous power into an 8-ohm speaker when operating from a 3-V to 5-V power supply with less than 1 percent total harmonic distortion plus noise (THD+N). It drives an 8-ohm speaker load at 3-W continuous power to enable louder speaker volumes for manufacturers of push-to-talk cell phones, portable global positioning systems (GPS) and MP3 docking stations with portable speakers, as well as a broad range of other battery-powered applications.

The gain of the LM48511 is set by external resistors, which allows independent gain control from multiple sources by summing the signals, said National. The LM48511 features a low-power consumption shutdown mode as well as output short-circuit and thermal overload protection. Advanced pop-and-click circuitry eliminates output transients which would otherwise occur during power or shutdown cycles. The amplifier also includes selectable feedback networks that allow the designer to scale power and manage efficiency.

The LM48511 uses National's unique spread spectrum technology to lower electromagnetic interference (EMI) emissions more than 11 dB below the Federal Communications Commission (FCC) limit. The LM48511's 80 percent efficiency at 5 V extends battery life when compared to boosted Class AB amplifiers, and its independent regulator and amplifier shutdown controls also optimize power savings by disabling the regulator when high output power is not required, said National.

Pricing: Available now in a 24-pin LLP package, the LM48511 is priced at $1.75 in quantities of 1,000.
Product information: LM48511, audio amplifiers, PowerWise brand products, and WEBENCH online design tool

National Semiconductor , www.national.com

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