20W stereo Class D speaker amplifier
Maxim Integrated Products introduces the MAX9744, a 20W stereo Class D speaker amplifier to operate from a 4.5V to 14V power supply. The MAX9744 provides ample output power throughout the power-supply voltage range, making it ideal for MP3 docking stations, gaming consoles, and flat-panel televisions. Additionally, the device integrates 64-step analog and digital volume control. In analog mode, the volume range is ratiometric relative to VDD. To ramp up or down the volume digitally, the system microcontroller can program a 6-bit register through the MAX9744's I²C interface. External feedback resistors set the input gain, while the output has an internally set gain. When powered from a 12V supply, the amplifier combines these gains with the wide volume-control range, and delivers 20W per channel into 4Ω speakers.
Class D amplifiers are known for high power efficiency, and the MAX9744 does not disappoint with its 93% efficiency while delivering 20W into an 8Ω load. Achieving high 75dB PSRR, low 0.04% THD+N, and greater than 90dB SNR, this stereo amplifier offers Class AB performance with Class D efficiency. Due to the switching nature of the output stage, most Class D amplifiers require large, costly output filters; exhibit poor THD+N; and radiate electromagnetic interference (EMI). The MAX9744, however, employs Maxim's patented spread-spectrum modulation to reduce the peaks of the fundamental and subsequent harmonics by spreading energy over a wider bandwidth. This device also offers a filterless modulation mode, which eliminates the large LC filters required by traditional Class D amplifiers.
These two modulation schemes minimize design cost and space, and they eliminate the time-to-market problems associated with EMI radiation. The MAX9744 includes a low-power shutdown mode, a mute function, and integrated click-and-pop suppression. Available in a 7mm x 7mm x 0.8mm, 44-pin TQFN package, the device is fully specified over the -40°C to +85°C extended temperature range. An evaluation kit is available to speed design implementation. Pricing starts at $2.45 (1000-up, FOB USA).