National Semiconductor Expands Family of World's Smallest Audio Amplifiers
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National Semiconductor Expands Family of World's Smallest Audio Amplifiers

New Boomer Class AB Mono Amplifier and Stereo Headphone Amplifier Expand Portfolio of Mini Chips for Space-Constrained Portable Applications

SANTA CLARA, Calif., Aug. 14 /PRNewswire-FirstCall/ -- National Semiconductor Corporation (NYSE: NSM) today introduced two Boomer(R) Class AB amplifiers in a 0.4 mm-pitch package, the world's smallest micro SMD package. The LM4941 1.25W audio amplifier and LM4985 stereo headphone amplifier provide low quiescent current and high output power, extending battery life in portable electronic devices, MP3 players, mobile phones and other similar applications.

National's 0.4 mm-pitch micro SMD package uses very little space on a printed circuit board, facilitating easier layout in small spaces. Developed by National engineers, this package is the next generation of the industry- leading micro SMD packaging family originated by National in 1999. This package utilizes advanced manufacturing processes for making silicon, bumping and back-grinding technologies.

The LM4941 Class AB, 1.2W audio amplifier integrates National's unique RF suppression circuitry, which provides up to a 20 dB improvement over existing designs. This RF circuitry prevents the outputs from acting as antennas that can pick up noise and inject it back into the amplifier signal path. This 1.2 mm by 1.2 mm fully differential amp rejects the common-mode noise found in most systems and offers a low quiescent current of 1.7 mA at a 5V supply.

With an I2C compatible controlled, 32-step, non-linear volume control, the LM4985 low-noise stereo headphone amplifier reduces the need for software to increase the system's volume-control resolution. To improve the customer's listening experience, the volume control curve is tailored for the human ear. The amp has a low quiescent current of 3 mA, dual channel in OCL mode and 135 mW per channel of continuous average power into a 16-Ohm load from a 5V power supply.

The LM4985 may be used as either a capacitive-coupled or output capacitor-less (OCL) device for design flexibility, while also allowing companies to speed product qualification by creating additional platforms using this one National amplifier.

Key Technical Features and Benefits

The LM4941 delivers 1.25W of continuous power to an 8-Ohm .load with 0.04 percent total harmonic distortion plus noise (THD+N) from a 5V power supply. It has a typical power supply rejection ratio (PSRR) of 95 dB at 217 Hz and a signal-to-noise ratio (SNR) of 108 dB at 1kHz. The amp also provides a mono speaker output.

At 1 percent THD from a 3.6V power supply, the LM4985 delivers 68 mW per channel of continuous average power into a 16-Ohm load or 38 mW per channel into a 32-Ohm load when operating in OCL mode. Its I2C compatible volume control allows 18 db to -76 db gain settings. At very low volumes, where the human ear needs a large jump in volume to identify the change, the step sizes are large. At high volumes, where the human ear can discern much smaller level changes, step sizes are very small. It also has a PSRR of 77 dB at 217 Hz in OCL mode.

Both chips work without output coupling capacitors or bootstrap capacitors and feature an internal thermal shutdown protection mechanism. Their advanced pop & click circuitry eliminates noises which would otherwise occur during turn-on and turn-off transitions.

World's Smallest Class AB and D Amplifiers

The LM4985 and LM4941 join two previously announced amplifiers, the LM4673 and LM4995, in the 0.4 mm-pitch micro SMD package. The LM4673 is a fully differential, single-supply, filter-less, 2.5W Class D switching audio amplifier in a 1.4 mm by 1.4 mm micro SMD package, allowing designers to place the chip very close to speakers, virtually eliminating electromagnetic interference (EMI). Consuming less power than any similar Class D audio amplifier available today, the LM4673 has a typical quiescent current of 2.1 mA at a 3.6V supply, enabling longer talk times in mobile phones and more listening time for portable audio devices.

The LM4995 Class AB amplifier is a housed in a 1.25 mm by 1.25 mm micro SMD package, which uses 30 percent less space on the printed circuit board than existing audio amplifiers. Operating on a single 5V supply, it is capable of driving an 8-Ohm speaker load at a continuous average output of 1.3W with less than 1 percent THD+N.

Innovative, Advanced IC Package Technologies

National packages its chips in more than 70 different package types. The company holds more than 290 patents in package technologies and receives approximately 30 new packaging patents each year. National has introduced several packaging innovations to the industry, including both the micro SMD and LLP(R) packaging technologies.

Pricing and Availability

Available now, the LM4985 is priced at $1.46 and the LM4941 is priced at 62 cents, both in 1,000-unit quantities. More information and easy-to-order samples are available at and . To learn about audio amplifiers for portable applications, visit National's library of online seminars at .

About National's Audio Portfolio

National Semiconductor works with every major handset maker in the world and is the leading provider of audio amplifier systems for the cell phone market. The company's line of Boomer audio amplifiers enhances and enriches the entire range of sound -- from voice, ring sounds and music -- that can be amplified in a mobile phone. National manufactures Class AB and Class D mono and stereo speaker amplifiers, mono and stereo headphone amplifiers, and audio subsystems for desktop and notebook computers, multimedia displays and portable electronic devices. The company also offers its higher-power Overture(R) amplifiers for consumer stereo and home theater systems. National's WEBENCH(R) online design tool supports a large selection of audio amplifiers. To explore these solutions, visit . For more information on National's audio products, visit

About National Semiconductor

National Semiconductor, the industry's premier analog company, creates high-value analog devices and subsystems. National's leading-edge products include power management circuits, display drivers, audio and operational amplifiers, interface products and data conversion solutions. National's key analog markets include wireless handsets, displays and a variety of broad electronics markets, including medical, automotive, industrial, and test and measurement applications. Headquartered in Santa Clara, Calif., National reported sales of $2.16 billion for fiscal 2006, which ended May 28, 2006. Additional company and product information is available at

NOTE: Boomer, Overture, LLP and WEBENCH are registered trademarks of National Semiconductor Corporation.

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