9.3.17 Spread Spectrum vs Synchronized

The Class-D switching frequency can be selected to work in three different modes of operations selected by Table 21. This configuration needs to be done before powering up the audio channel. The first is a synchronized mode where the Class-D frequency is synchronized to audio input sample rate. This is the default mode of operation and can 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 or 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 using field RAMP_FREQ.

The second mode is fixed-frequency mode and the ramp is generated from the internal oscillator. The internal oscillators across chips will vary slightly and this can create an intermodulation beating in application where more than one TAS2560 is used.

The last mode is spread-spectrum mode and used to reduce wideband spectral content. This can improve EMI emissions radiated by the speaker by spreading out the noise in the spectrum. In this mode, the Class-D switching frequency varies +-5% or +-10% base on the Table 23 around the Table 22 around a 384 kHz center frequency. These registers should be written before powering up the audio channel.