Datasheet MAX9700 (Maxim) - 8

MAX9700 1.2W, Low-EMI, Filterless, Class D Audio Amplifier
Pin Description PIN BUMP NAME FUNCTION TDFN/µMAX UCSP
1 A1 V Analog Power Supply. Connect to an external power supply. Bypass to GND with a DD 1µF capacitor. 2 B1 IN+ Noninverting Audio Input 3 C1 IN- Inverting Audio Input 4 C2 GND Analog Ground 5 B2 SHDN Active-Low Shutdown Input. Connect to VDD for normal operation. Frequency Select and External Clock Input.
SYNC = GND:
Fixed-frequency mode with fS = 1100kHz. 6 A3 SYNC
SYNC = Unconnected:
Fixed-frequency mode with fS = 1450kHz.
SYNC = VDD:
Spread-spectrum mode with fS = 1220kH ±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. Exposed Pad. Internallly connected to GND. Connect to a large ground plane to — — EP maximize thermal performance. Not intended as an electrical connection point. (TDFN package only.)
Detailed Description Operating Modes
The MAX9700 filterless, class D audio power amplifier
Fixed-Frequency Modulation (FFM) Mode
features several improvements to switch-mode amplifier The MAX9700 features two FFM modes. The FFM modes technology. The MAX9700 offers class AB performance are selected by setting SYNC = GND for a 1.1MHz switching with class D efficiency, while occupying minimal board frequency, and SYNC = UNCONNECTED for a 1.45MHz space. A unique filterless modulation scheme, synchroniz- switching frequency. In FFM mode, the frequency spectrum able switching frequency, and SSM mode create a com- of the class D output consists of the fundamental switching pact, flexible, low-noise, efficient audio power amplifier. frequency and its associated harmonics (see the Wideband The differential input architecture reduces common-mode FFT graph in the Typical Operating Characteristics). The noise pickup, and can be used without input-coupling MAX9700 allows the switching frequency to be changed by capacitors. The device can also be configured as a single- +32%, should the frequency of one or more of the harmon- ended input amplifier. ics fall in a sensitive band. This can be done at any time Comparators monitor the MAX9700 inputs and compare and does not affect audio reproduction. the complementary input voltages to the sawtooth wave- form. The comparators trip when the input magnitude of
Spread-Spectrum Modulation (SSM) Mode
the sawtooth exceeds their corresponding input voltage. The MAX9700 features a unique spread-spectrum Both comparators reset at a fixed time after the rising mode that flattens the wideband spectral components, edge of the second comparator trip point, generating a improving EMI emissions that may be radiated by the minimum-width pulse t speaker and cables by 5dB. Proprietary techniques ON(MIN) at the output of the sec- ond comparator (Figure 1). As the input voltage increases ensure that the cycle-to-cycle variation of the switch- or decreases, the duration of the pulse at one output ing period does not degrade audio reproduction or effi- increases (the first comparator to trip) while the other ciency (see the Typical Operating Characteristics). Select output pulse duration remains at t SSM mode by setting SYNC = V ON(MIN). This causes DD. In SSM mode, the net voltage across the speaker (V the switching frequency varies randomly by ±120kHz OUT+ - VOUT-) to change. around the center frequency (1.22MHz). The modulation scheme remains the same, but the period of the saw- www.maximintegrated.com Maxim Integrated │ 8