TDA7572 Datasheet, PDF (53/64 Pages) STMicroelectronics – 200W mono bridge PWM amplifier with built-in step-up converter

TDA7572
11 Oscillator
Oscillator
A common clock is needed to run all switching blocks at one frequency to avoid beating. The
internally generated clock is used for the PWM modulators and to run the dc-dc converter.
To blur the EMI spectrum, sub-audible frequency dither incorporated.
● When the DITH-sel pin is logic gnd then the internal oscillator operates without dither.
● With a cap there is +-100UA dithering functions
● Putting DITH-sel to VDIG allows an external clock to be accepted from CLKin-out at 4X
the selected frequency
● Clock out is referred to VP2.5 and VM2.5, while external clock input is referred to
DGND and VDIG
● External CLKin-out is always active. When DITH-sel is different to VDIG on this pin is
present a 4X modulator frequency at digital level.
The dither acts to span the intermodulation products present around multiple of switching
frequency. Dither the modulator frequency means make it slowly changing around a nominal
value. In case of a capacitor is connected to the DITH-sel pin a triangular drop is present
across it and the modulator frequency value follows these behave. The maximum value
reaches by it is the nominal value plus 10%, while the minimum value is nominal one minus
10%. This pick frequency values are reached when the DITH-sel pin reach the maximum
voltage value. The value of capacitor is involved in the ratio of variation of modulator
frequency, provided that it acts on triangular wave frequency.
In case of DAC operation the modulator frequency of PWM digital out of this component is
lock to the I2S input frequency, which is different from the analog modulator frequency
imposed by the described oscillator. No high value intermodulation product are generated
by difference of this frequency because the presence of filter between DAC out and Diff-to-
SE input. However a multiple frequency of DAC could be imposed to analog modulator by
the CLKin-out pin. In this case no dither can be introduced.
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