NATIONAL SEMICONDUCTOR INTRODUCES HIGH-EFFICIENCY, HIGH-FIDELITY, 2.0W CLASS D STEREO AUDIO AMPLIFIER IC

The LM4663's 83% Efficiency Makes it Ideal for Battery Powered Applications Such as Notebook Computers

February 28, 2000 - National Semiconductor Corporation (NYSE:NSM) today announced the LM4663, a high-efficiency, high-fidelity Class D stereo audio amplifier IC. The LM4663 can output 2.0W per channel of RMS power into a 4W load with less than 0.2% THD+N. The LM4663's efficiency for typical average music signals is approximately 69%, while its efficiency reaches 83% at 2W of power into a 4W load. The LM4663 also has a stereo headphone amplifier that delivers 70mW of power into a 32W headset with typically 0.15% THD. The LM4663 has two stereo inputs, either of which can be selected by the user to drive either the headphone amplifier or the Class D amplifier.

While conventional Class AB audio amplifiers are typically only 50% efficient, the LM4663's advanced architecture makes it up to 83% efficient. This extra efficiency translates directly into less wasted energy in the form of heat that must be dissipated, eliminating bulky heatsinks and allowing components to be packed more tightly. The higher efficiency also leads to significantly longer battery life for portable applications.

Possible applications for the LM4663 include, but are not limited to, notebook and desktop computers, multimedia monitors, PDAs (personal digital assistants), "boom boxes," powered speakers and other power-limited applications.

"As supply voltages for digital circuitry continues to drop, audio amplifiers must become more efficient, with lower power dissipation to deliver the required performance - especially for portable applications. The LM4663 is the most efficient audio amplifier available below 5.5V," says Steve Kaufman, product marketing manager, Audio group at National Semiconductor.

Conventional Class AB audio amplifiers have much in common with linear voltage regulators. Linear amplifiers "throttle" the power delivered to the load by dissipating the power not required by the load in the form of heat, leading to a significant waste of power.

In contrast, Class D audio amplifiers use pulse width modulation techniques similar to those employed in switching power supplies. In particular, the LM4663 uses a continuous time delta-sigma modulation technique that lowers output noise, as well as THD, compared to conventional pulse width modulators. It applies high-frequency square waves of constant frequency and voltage level, but having variable pulse widths, to the load. The audio signals are "encoded" in the widths of the pulses. The square waves are then low-pass filtered to smooth the signal and extract the audio information. Because the circuits that develop the square waves in the LM4663 are mostly either fully on or fully off, little power is wasted in the IC itself.

The device's quiescent current is 22mA (typ). The LM4663's extremely low supply current in standby mode is 2µA (max). The LM4663 also features click and pop reduction circuitry to minimize audible popping upon device turn-on and turn-off and a thermal shutdown feature.

Pricing and Availability
Available now in a space-saving 24 lead TSSOP package, the LM4663 costs only $3.30 each in 1000 unit quantities. For more information, please visit http://www.national.com/pf/LM/LM4663.html or contact National's Customer Response Group at 1-800-272-9959.

About National Semiconductor
National Semiconductor provides system-on-a-chip solutions for the information age. Combining real-world analog and state-of the-art digital technology, the company's chips lead many sectors of the personal computer, communications, and consumer markets. With headquarters in Santa Clara, California, National reported sales of $2 billion for its last fiscal year and has about 10,500 employees worldwide. Additional company and product information is available on the World Wide Web at www.national.com.