TDA7491LP datasheet(28/37 Pages) STMICROELECTRONICS

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TDA7491LP

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Doc ID 13541 Rev 5

5.6

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 on the load then reducing the current ripple accordingly. The

OUTP and OUTN are in the same phase almost overlapped when the input is zero under

this condition, then the switching current is low and the related losses in the load are low. In

practice, a short delay is introduced between these two outputs in order to avoid the BTL

outputs switching simultaneously when the input is zero.

Figure 31 shows the resulting differential output voltage and current when a positive, zero

and negative input signal is applied. The resulting differential voltage on the load has a

double frequency with respect to outputs OUTP and OUTN then resulting in reduced current

ripple.

Figure 31.

Unipolar PWM output

INP

INN

OUTP

OUTN

Differential

OUT

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