TDA7491LP13TR Datasheet, PDF (28/37 Pages) STMicroelectronics – 2 x 5-watt dual BTL class-D audio amplifier

Applications information
TDA7491LP
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 +V_CC and between 0 V and -V_CC.
This is in contrast to the traditional bipolar PWM outputs which change between +V_CC
and -V_CC.
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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Doc ID 13541 Rev 5