NATIONAL SEMICONDUCTOR INTRODUCES WORLD'S FIRST 170 WATT, 85% EFFICIENT CLASS D AUDIO POWER AMPLIFIER CHIPSET FOR COMPACT, HIGH-FIDELITY SUBWOOFER DESIGNS

LM4651/52 Chipset Offers State of the Art Class D IC Amplifier Technology That Reduces Heat Sink and Power Supply Requirements

March 20, 2000- National Semiconductor Corporation (NYSE:NSM) today announced the LM4651 and LM4652, a two-chip driver and quad MOSFET amplifier set for high-fidelity Class D subwoofer designs. This chipset provides up to 170 watts of audio power at an excellent 85% efficiency, with smaller space and lower cost. In comparison, Class AB amplifiers are only 50 to 60% efficient. This highly integrated LM4651 and LM4652 set eliminates the need for large power supplies, heat sinks and transformers to help achieve compact designs. The LM4651 and LM4652 chipset offers the highest power in its proprietary two-chip solution and delivers power levels usually found only in discrete implementations that add part count, complexity and cost.

"This chipset is a breakthrough in the design of Class D subwoofer products. By having an integrated driver and a quad MOSFET, our customers using the LM4651 and LM4652 will be able to build more compact subwoofers with virtually no heat sink and a much smaller power supply," said Steve Kaufman, product marketing manager for National's audio group. "Because of its increased efficiency, the new chipset requires a smaller power supply, transformer and heat sink, which adds up to compact solutions, less design complexity and lower cost over competitors' Class D designs."

Besides subwoofers, intended applications include car-booster amplifiers and other self-powered speakers.

A fully-integrated pulse-width modulation driver IC, LM4651 contains short-circuit, under-voltage, over-modulation and thermal-shutdown protection circuitry. The IC also contains a standby function that shuts down the pulse width modulation and minimizes supply current.

A fully-integrated H-bridge power MOSFET IC, the LM4652 incorporates four MOSFETs to cut part count and reduce EMI radiation by minimizing trace length between the LM4652 and the LM4651. The two ICs require no external components between them, keeping board area small and also aiding EMI control.

By eliminating the need for four external MOSFETs, the two ICs simplify the design of Class D amplifiers. Unlike designs using external MOSFETs, this chipset is tightly coupled through feedback circuits that continuously monitor the temperature in both ICs by a thermal shutdown protection circuit.

Other key specifications include an externally controllable switching frequency from 50kHz to 225kHz; integrated error and feedback amplifiers; turn on soft start and under-voltage lockout; and a self-checking protected diagnostic. Standby attenuation is 100dB minimum and total harmonic distortion (THD) is less than 0.3% typically at 10W, and 4 Ohms between 10 and 500Hz.

Pricing and Availability
Available now, the LM4651N, housed in a 28-lead plastic DIP package, is priced at $4.65 in 1000-unit quantities. The LM4652TF, housed in a 15-lead isolated TO-220 package, is priced at $4.25 each in 1000-unit quantities. For more information on the LM4651 and LM4652, visit National's World Wide Web site at http://www.national.com/pf/LM/LM4651.html and http://www.national.com/pf/LM/LM4652.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.