TDA7572 datasheet(53/64 Pages) STMICROELECTRONICS

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TDA7572

Oscillator

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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.

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When the DITH-sel pin is logic gnd then the internal oscillator operates without dither.

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With a cap there is +-100UA dithering functions

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Putting DITH-sel to VDIG allows an external clock to be accepted from CLKin-out at 4X

the selected frequency

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Clock out is referred to VP2.5 and VM2.5, while external clock input is referred to

DGND and VDIG

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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.

TDA7572 Datasheet(PDF) 53 Page - STMicroelectronics