Class-D Amplifiers Tackle Wide Range Of Applications December 2004 Issue Published Date: January 06, 2005
A pair of class-D audio amplifiers is designed for two distinct needs in consumer products. The LM4666 is a stereo speaker amplifier for cellular phones and other portable electronics while the LM46668 is a switching power amplifier for flat-panel monitors, TVs and computer sound cards. The LM4666 is a 1.3 W/channel, fully differential amplifier with selectable gain of 6- to 12-dB. High efficiency reduces power consumption and minimizes heat dissipation, resulting in extended battery life and increased talk time in cellular phones. Delta-sigma modulation techniques reduces output noise and total harmonic distortion (THD) compared to conventional pulse-width modulation (PWM) amplifiers. The LM4668 is a 10W mono audio power amplifier with a gain of 30 dB. It delivers 10W into an 8Ω load at 10% THD plus noise (THD +N) from a 14V power supply. It uses a balanced PWM that increases noise immunity. The LM4446 comes in a 14-lead LLP package. The LM4448 also comes in the 14-lead LLP and in a 20-lead TSSOP. Prices for the LM4446 and LM4448 $0.90 and $1.58 each/1,000, respectively. NATIONAL SEMICONDUCTOR, Santa Clara, CA. (800) 272-9959.
