SLASEC2B November 2016 – February 2019 TAS2557
The Class-D switching frequency can be selected to work in two different modes of operations. 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 the 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 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 Table 10.
The second mode uses the internal oscillator to generate the ramp clock. This is enabled using Table 11. This mode is generally used with Table 12 enabled for spread-spectrum. Spread-specturm is used to reduce wideband spectral content improving EMI emissions radiated by the speaker. In this mode, the Class-D switching frequency can varies ±5% or ±10% as set by Table 13 about the set frequency Table 10.
The configuration for this block should be set using the PurePath Console 3 Software TAS2557 Application software for the TAS2557 part under the Device Control Tab.
|00||384 kHz (default)|
|0||Sync Mode - ramp generated from digital audio clock (default)|
|1||Fixed Frequency Mode(FFM) - ramp generated from internal oscillator|
|0||SSM mode is disabled|
|1||SSM mode is enabled(1)|
|01||SSM mode enabled with ramp frequency modulated for ±5 % (default)|
|10||SSM mode enabled with ramp frequency modulated for ±10 %|