9.3.10.3 Spread Spectrum vs Synchronized

The Class-D switching frequency can be selected to work in two different modes of operations. This configuration must be done before powering up the audio channel. The first is a synchronized mode where the Class-D frequency is synchronized frequency to audio input sample rate. This is the default mode of operation and should be used in stereo applications to avoid inter-modulation beating of the Class-D frequency from multiple chips. The Class-D switching frequency in this mode can be configured as 384 kHz for 352.8 kHz. The 384 kHz frequency is the default mode of operation, and can be used for input signals running on clock rates of 48 kHz or its sub-multiples. For input signals running on clock rate of 44.1 kHz and its sub-multiples, the switching frequency can be selected as 352.8 kHz by setting B0_P2_R6[4]=1.

The second mode is spread-spectrum mode used to reduce wideband spectral content, improving EMI emissions radiated by the speaker. In this mode, the Class-D switching frequency varies +-5% about a 384 kHz center frequency. This mode can be configured by setting B0_P0_R40[0]=1 and B100_P0_R40[7]=0. Both these registers should be written before powering up the audio channel.