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National Semiconductor Introduces World’s Smallest Class D Audio Amplifiers

Mono and Stereo Filter-less Amplifiers Maximize Performance, Power Savings While Saving Valuable Board Space

Dec 19, 2005

December 19, 2005 - To save even more space in portable applications, National Semiconductor Corporation (NYSE:NSM) today introduced a Boomer® mono Class D audio amplifier in the world’s smallest micro SMD package.  In addition, the company introduced a high-power stereo Class D amplifier. Both provide high-quality output power with a minimal number of external components for cell phones, smart phones and portable audio devices such as DVD players and gaming devices.

"National’s Class D audio amplifier portfolio continues to meet our customers’ design requirements for great audio performance in small, low-power, low-heat portable applications,” said Mike Polacek, vice president of National Semiconductor’s Audio group.  “Our new LM4673 mono Class D amplifier comes in a tiny, 0.4 mm-pitch micro SMD package to save space in manufacturers’ designs. The stereo LM4674 Class D amplifier also provides great board-space efficiency for stereo applications.”

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, 0.4 mm-pitch micro SMD package.  This package, which uses very little space on the printed circuit board, facilitates easier layout in small spaces. For example, the chip can be placed 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 LM4674 is a filterless, 2.4W stereo Class D audio power amplifier available in a 2 mm by 2 mm, 0.5 mm-pitch package.  The chip also has a typical quiescent current of 4 mA at a 3.6V supply for power savings.

Key Technical Features and Benefits
National’s LM4673 and LM4674 audio amplifiers employ a low-noise, filter-less pulse-width modulation architecture that eliminates output filters, reducing external component count, saving space on the board layout, lowering system cost and simplifying the circuit design. The flexible power supply requirements of these parts allow operation from 2.4V to 5.5V. 

Both of these Class D amplifiers have high efficiency with speaker loads compared to typical Class AB amplifiers.  Each product features a low-power shutdown mode and internal, advanced “pop and click” circuitry that eliminates output transients which would otherwise occur during power or shutdown cycles. The gain of the LM4673 is externally configurable to allow the user to connect different multiple inputs while optimizing the gain for each source. 

Operating on a single 5V supply, the LM4673 is capable of driving a 4-Ohm speaker load at a continuous average output of 2.5W with less than one percent total harmonic distortion plus noise (THD+N). In addition to its low quiescent current, the LM4673 offers a power supply rejection radio (PSRR) of 78 dB at 217 Hz, a common-mode rejection ratio (CMRR) of 70 dB and a signal-to-noise ratio (SNR) of 97 dB. It also has a typical fast turn-on time of 17 microseconds.

The LM4674 delivers 2.4W per channel of continuous output power to a 4-Ohm load with 10 percent THD+N.  The chip features independent left and right shutdown controls to maximize power savings in mixed mono and stereo applications. To give designers flexibility, the LM4674 has four gain settings of 6 dB, 12 dB, 18 dB and 24 dB.  The chip also has a PSRR of 75 db at 217 Hz.

Innovative, Advanced IC Package Technologies
Developed by National engineers in Santa Clara, California, and Melaka, Malaysia, the 0.4 mm- pitch micro SMD package is the next generation of the industry-leading micro SMD packaging family that National originated in 1999.  This new package utilizes advanced manufacturing processes for making silicon, bumping and back-grinding technologies. Manufacturers can use the package with conventional surface-mount handling equipment.

National produces billions of chips per year and packages them in more than 70 different package types.  The company has 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® packaging technologies.

Pricing and Availability
Available now, the LM4673 is priced at 90 cents in a lead-free, 9-bump micro SMD package. The LM4674 is offered in a standard or lead-free, 16-bump micro SMD package and is priced at $1.50.  Both prices are for 1,000-unit quantities. More information and easy-to-order samples are available at http://www.national.com/pf/LM/LM4673.html and  http://www.national.com/pf/LM/LM4674.html.  National’s WEBENCH® online design tool supports a large selection of audio amplifiers.  To explore these solutions, visit http://webench.national.com.  To learn about high-performance audio amplifiers for portable applications, visit National’s library of online seminars

Note to editors:  To view a high-resolution, downloadable photo of this product, visit National's photo gallery.

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® amplifiers for consumer stereo and home theater systems.  For more information on National’s audio products, visit audio.national.com.

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, communication 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, California, National reported sales of $1.91 billion for fiscal 2005, which ended May 29, 2005.  Additional company and product information is available at www.national.com.