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20W Stereo Class D Speaker Amplifier with Analog and Digital Volume Control Operates from a 4.5V to 14V Supply

Maxim Integrated Products (PINK OTC MARKETS: MXIM) introduces the MAX9744, the industry’s first 20W stereo Class D speaker amplifier to operate from a 4.5V to 14V power supply. The wide supply range minimizes the cost of portable designs by reducing component count and allowing the use of a smaller battery pack. 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 MAX9744 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 MAX9744 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.

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