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MAX9700 Datasheet(PDF) 8 Page - Maxim Integrated Products |
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MAX9700 Datasheet(HTML) 8 Page - Maxim Integrated Products |
8 / 20 page 1.2W, Low-EMI, Filterless, Class D Audio Amplifier 8 _______________________________________________________________________________________ Detailed Description The MAX9700 filterless, class D audio power amplifier features several improvements to switch-mode amplifier technology. The MAX9700 offers class AB performance with class D efficiency, while occupying minimal board space. A unique filterless modulation scheme, synchro- nizable switching frequency, and SSM mode create a compact, flexible, low-noise, efficient audio power amplifier. The differential input architecture reduces common-mode noise pickup, and can be used without input-coupling capacitors. The device can also be con- figured as a single-ended input amplifier. Comparators monitor the MAX9700 inputs and com- pare the complementary input voltages to the sawtooth waveform. The comparators trip when the input magni- tude of the sawtooth exceeds their corresponding input voltage. Both comparators reset at a fixed time after the rising edge of the second comparator trip point, gener- ating a minimum-width pulse tON(MIN) at the output of the second comparator (Figure 1). As the input voltage increases or decreases, the duration of the pulse at one output increases (the first comparator to trip) while the other output pulse duration remains at tON(MIN). This causes the net voltage across the speaker (VOUT+ - VOUT-) to change. Operating Modes Fixed-Frequency Modulation (FFM) Mode The MAX9700 features two FFM modes. The FFM modes are selected by setting SYNC = GND for a 1.1MHz switching frequency, and SYNC = UNCONNECTED for a 1.45MHz switching frequency. In FFM mode, the fre- quency spectrum of the class D output consists of the fundamental switching frequency and its associated harmonics (see the Wideband FFT graph in the Typical Operating Characteristics). The MAX9700 allows the switching frequency to be changed by +32%, should the frequency of one or more of the harmonics fall in a sensitive band. This can be done at any time and does not affect audio reproduction. Spread-Spectrum Modulation (SSM) Mode The MAX9700 features a unique, patented spread-spec- trum mode that flattens the wideband spectral compo- nents, improving EMI emissions that may be radiated by the speaker and cables by 5dB. Proprietary techniques ensure that the cycle-to-cycle variation of the switching period does not degrade audio reproduction or efficien- cy (see the Typical Operating Characteristics). Select SSM mode by setting SYNC = VDD. In SSM mode, the switching frequency varies randomly by ±120kHz around the center frequency (1.22MHz). The modulation Pin Description PIN BUMP TDFN/µMAX UCSP NAME FUNCTION 1A1 VDD Analog Power Supply. Connect to an external power supply. Bypass to GND with a 1µF capacitor. 2 B1 IN+ Noninverting Audio Input 3 C1 IN- Inverting Audio Input 4 C2 GND Analog Ground 5B2 SHDN Active-Low Shutdown Input. Connect to VDD for normal operation. 6 A3 SYNC Frequency Select and External Clock Input. SYNC = GND: Fixed-frequency mode with fS = 1100kHz. SYNC = Unconnected: Fixed-frequency mode with fS = 1450kHz. SYNC = VDD: Spread-spectrum mode with fS = 1220kHz ±120kHz. SYNC = Clocked: Fixed-frequency mode with fS = external clock frequency. 7 B3 PGND Power Ground 8 A4 OUT+ Amplifier-Output Positive Phase 9 C4 OUT- Amplifier-Output Negative Phase 10 B4 PVDD H-Bridge Power Supply. Connect to VDD. —— EP Exposed Pad. Internallly connected to GND. Connect to a large ground plane to maximize thermal performance. Not intended as an electrical connection point. (TDFN package only.) |
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