NATIONAL SEMICONDUCTOR INTRODUCES COMPLETE BIAS SUPPLY FOR GAASFET POWER AMPS

LM2687, with Only +1mV Output Ripple, Generates a Very Low Noise Negative Regulated Voltage for Cellular Phones

September 13, 1999 - National Semiconductor® Corporation (NYSE:NSM) today announced the LM2687, a negative regulated switched capacitor voltage inverter that generates a low noise negative bias to control the output power of gallium arsenide (GaAs) power amplifiers in cellular phones. Housed in a small MSOP-8 package, the inductorless LM2687 typically produces just +1mV output ripple with <1mS startup time, prolonging battery life and simplifying power amplifier design.

"The GaAs power amplifier continues to garner the vast majority of new designs due to its superior power efficiency. We designed the LM2687 in response to our customers' desire for a monolithic solution that generates a low current, high accuracy, very low noise negative bias for these cellular phone power amplifiers," said Jim Schuessler, senior technical marketing manager for National's Power Management Group. "The LM2687, with its extremely low output ripple and quick startup time, is applicable to a broad range of current and emerging cellular phone standards."

In cellular phones, the negative bias controls output power, and any ripple on that supply could directly modulate the output signal and contribute to RF distortion, making the phone incompatible with cellular telephone standards. Designed to generate a very low noise negative regulated voltage, the LM2687 inverts a positive voltage in the range of +2.7 to +5.5V. This input range allows the LM2687 to be powered directly from the lithium-ion battery or fixed, lower noise power sources. The voltage is then regulated by an adjustable low dropout (LDO) linear regulator to provide up to 10mA between -1.5 and -4.5V. The low +1mV output ripple of the LM2687 is well below the threshold of concern for RF distortion. In addition, the short start-up time of <1mS saves battery life and allows the LM2687 to be used in TDMA communication protocols such as PDC in Japan and GSM worldwide.

The LM2687 is a monolithic solution that replaces discrete switched capacitor inverters, operational amplifiers and LDOs. Its integrated design saves space, eases manufacturing requirements and minimizes design time. The LM2687's small, thin MSOP-8 package is half the size of most competitors' solutions, minimizing board space and solution volume.

Price and Availability
The LM2687 is priced at $0.80 when purchased in quantities of 1,000. For more information on the LM2687, visit National's World Wide Web site at http://www.national.com/pf/LM/LM2687.html.

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 currently has about 11,000 employees worldwide. Additional company and product information is available on the World Wide Web at www.national.com.