Electronic Design

Efficient Class-D Audio Power Amplifier Eliminates Output Filter

Texas Instruments recently unveiled a new line of efficient class-D audio power amplifiers, called the TPA200xD family. The first member of this family is a stereo class-D amplifier that exploits an improved pulse-width modulation (PWM) scheme, as well as a linear biCMOS (LBC) process to more than double the amplifier's efficiency. In addition, it eliminates the bulky output LC filter to achieve significant savings in both cost and board space.

"The output filter is a killer," notes Ted Thomas, new product development manager at TI. "Plus, the LBC 3.0 process cuts both the size and the supply current of the new TPA2000D2, the first member of this family."

The reduction in size means a 50% smaller footprint than the previous introduction. A lower noise floor of −87 dB eliminates the background hiss. Also, the amplifier's total-harmonic distortion plus noise (THD+N) is only 0.5% at a 5-V supply in the high-fidelity range of 20 Hz to 20 kHz. Hence, the TPA2000D2 can deliver more than 2 W of continuous average power into 3-W speakers with excellent fidelity. By comparison, the new class-D power amplifier consumes nearly 2.5 times less supply current from the USB line, enabling bus-powered applications that weren't possible before.

Unlike typical class-D modulation, TI's new line uses a three-state PWM scheme that produces in-phase modulation to minimize ripple current in the load. It also reduces losses in the amplifier.

"There are no square waves at zero signal in the load," Thomas says. "Instead of square waves, you get small glitches at higher frequency to minimize ripple current in the load." This more than doubles the class-D amplifier's power efficiency to outperform the traditional class-AB linear amplifier.

The TPA2000D2 also provides four different gain settings across the audio band. These include 8.3, 12.4, 17.8, and 23.6 dB. Typical supply current is 6 mA. A shutdown control limits the supply current to below 1 mA. The inputs are fully differential. Housed in a 24-pin TSSOP, the TPA2000D2 is priced at $2.50 each in 1000-piece quantities.

Texas Instruments Inc., Semiconductor Group, P.O. Box 172228, Denver, CO 80217; (800) 477-8924; www.ti.com.

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