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National Semiconductor's Two Class D Boomer Audio Amplifiers Save Space and Extend Battery Life in Mobile Applications

New Audio Amps Eliminate External Parts, Enabling Smaller Footprint Devices and Simplifying Design

Mar 14, 2005

CTIA, NEW ORLEANS, LA - March 14, 2005 - National Semiconductor Corporation (NYSE:NSM) today introduced two new high-efficiency Class D audio amplifiers to its expansive Boomer® portfolio.  These new audio amplifiers are housed in tiny micro SMD packages and feature externally configurable gain for space savings and flexibility in design.  Additionally, they feature a low power consumption shutdown mode for extended battery life.  These two parts are ideal for applications such as cellular phones, PDAs and other portable electronic devices. 

"National continues to flex its analog muscles with its new Class D audio amplifiers,” said Mike Polacek, vice president of National Semiconductor’s Audio group.  “With features such as small footprint, high power, high efficiency and flexible gain settings, National’s LM4670 and LM4671 give customers the performance required for portable applications that continually expand in feature and power requirements.”

Outstanding Efficiency
National Semiconductor’s LM4670 is a 3W and the LM4671 is a 2.5W fully integrated single-supply, high-efficiency switching audio amplifier.  They feature innovative modulation schemes that eliminate the output filter used with typical switching amplifiers.  Eliminating the output filter reduces external component count, simplifies circuit design and reduces board area.  The LM4670 processes analog inputs with a delta-sigma modulation technique that lowers output noise and total harmonic distortion (THD).

Due to its high output power, the LM4670 is optimized for ultra-high-power push-to-talk, push-to-talk over cellular (PoC) and hands-free use.  The LM4671 processes analog inputs with a pulse width modulation technique that results in lower output noise, making it well suited for earpiece/receiver applications as well as normal high-power ringer and hands-free operation. 

Operating on a single 5V supply, the LM4670 and LM4671 are capable of driving a 4 Ohm speaker load at a continuous average output of 2.3W with less than one percent total harmonic distortion plus noise (THD+N).  Flexible power supply requirements of these parts allow operation from 2.4V to 5.5V.  The LM4670 and LM4671 have high efficiency with speaker loads compared to typical Class AB amplifiers.  With a 3.6V supply driving an 8 Ohm speaker, the amplifier’s efficiency is 88 percent at 600mW output power.  Additionally, the LM4670 and LM4671 feature a low power consumption shutdown mode.  Shutdown may be enabled by driving the shutdown pin to a logic low level.  Gain is externally configurable to allow the user to sum multiple inputs while optimizing the gain for each source. 

National's LM4670 and LM4671 audio amplifiers will be shown in National's booth #6645 at the CTIA tradeshow in New Orleans, Louisiana, from March 14-16.

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 http://audio.national.com

Pricing and Availability
Available now in 9-bump micro SMD packages, the LM4670 and LM4671 are priced at $0.48 in 1,000-unit quantities.  More information on the LM4670 is available at
http://www.national.com/pf/LM/LM4670.html and more information on the LM4671 is available at http://www.national.com/pf/LM/LM4671.html.  A large selection of audio amplifiers is supported by National’s WEBENCH® online design tool.  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 the new products, visit National's
photo gallery.

About National Semiconductor
National Semiconductor, the industry's premier analog company, creates high-performance 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 markets include wireless handsets, displays, PCs and laptops.  The company's analog products are also optimized for numerous applications in a variety of electronics markets, including medical, automotive, industrial, and test and measurement.  Headquartered in Santa Clara, California, National reported sales of $1.98 billion for fiscal 2004, which ended May 30, 2004.  Additional company and product information is available at www.national.com