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MAX9700BEBC-T Datasheet(PDF) 11 Page - Maxim Integrated Products |
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MAX9700BEBC-T Datasheet(HTML) 11 Page - Maxim Integrated Products |
11 / 20 page 1.2W, Low-EMI, Filterless, Class D Audio Amplifier ______________________________________________________________________________________ 11 Shutdown The MAX9700 has a shutdown mode that reduces power consumption and extends battery life. Driving SHDN low places the MAX9700 in a low-power (0.1µA) shutdown mode. Connect SHDN to VDD for normal operation. Click-and-Pop Suppression The MAX9700 features comprehensive click-and-pop suppression that eliminates audible transients on start- up and shutdown. While in shutdown, the H-bridge is in a high-impedance state. During startup or power-up, the input amplifiers are muted and an internal loop sets the modulator bias voltages to the correct levels, pre- venting clicks and pops when the H-bridge is subse- quently enabled. For 35ms following startup, a soft-start function gradually unmutes the input amplifiers. Applications Information Filterless Operation Traditional class D amplifiers require an output filter to recover the audio signal from the amplifier’s output. The filters add cost, increase the solution size of the amplifi- er, and can decrease efficiency. The traditional PWM scheme uses large differential output swings (2 x VDD peak-to-peak) and causes large ripple currents. Any parasitic resistance in the filter components results in a loss of power, lowering the efficiency. The MAX9700 does not require an output filter. The device relies on the inherent inductance of the speaker coil and the natural filtering of both the speaker and the human ear to recover the audio component of the square-wave output. Eliminating the output filter results in a smaller, less costly, more efficient solution. Because the frequency of the MAX9700 output is well beyond the bandwidth of most speakers, voice coil movement due to the square-wave frequency is very small. Although this movement is small, a speaker not designed to handle the additional power can be dam- aged. For optimum results, use a speaker with a series inductance >10µH. Typical 8Ω speakers exhibit series inductances in the 20µH to 100µH range. Power-Conversion Efficiency Unlike a class AB amplifier, the output offset voltage of a class D amplifier does not noticeably increase quies- cent current draw when a load is applied. This is due to Figure 3. MAX9700 EMI Spectrum 30.0 60.0 80.0 100.0 120.0 140.0 160.0 180.0 280.0 300.0 220.0 200.0 240.0 260.0 10.0 15.0 20.0 25.0 30.0 35.0 40.0 45.0 50.0 FREQUENCY (MHz) Figure 4. MAX9700 Outputs with No Input Signal VIN = 0V OUT- OUT+ VOUT+ - VOUT- = 0V Figure 5. MAX9700 Efficiency vs. Class AB Efficiency 0 30 20 10 50 40 90 80 70 60 100 0 0.1 0.2 0.4 0.6 0.3 0.5 0.7 EFFICIENCY vs. OUTPUT POWER OUTPUT POWER (W) MAX9700 CLASS AB VDD = 3.3V f = 1kHz RL - 8 Ω |
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