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TDA7491MV

Application information

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7.5

Filterless modulation

The output modulation scheme of the BTL is called unipolar pulse width modulation (PWM).

The differential output voltages change between 0 V and +VCC and between 0 V and -VCC.

This is in contrast to the traditional bipolar PWM outputs which change between +VCC

and -VCC.

An advantage of this scheme is that it effectively doubles the switching frequency of the

differential output waveform. The OUTP and OUTN are in the same phase when the input is

zero, then the switching current is low and the loss in the load is small. In practice, a short

delay is introduced between these two outputs in order to avoid the BTL output switching at

the same time.

TDA7491MV can be used without a filter before the speaker, because the frequency of the

TDA7491MV output is beyond the audio frequency, the audio signal can be recovered by

the inherent inductance of the speaker and natural filter of the human ear.

Figure 23. Unipolar PWM output

INP

INN

OUTP

OUTN

Differential

OUT