TDA749313TR Datasheet, PDF (13/30 Pages) STMicroelectronics – 3-watt 3-watt dual BTL class-D audio amplifier

TDA7493
Applications information
5.4
Filterless modulation
The modulation scheme of BTL is called unipolar PWM output. The differential output
voltage changes between zero and +V_CC or between zero and -V_CC, as opposed to the
traditional bipolar PWM output between +V_CC and -V_CC. The other advantage of this
scheme effectively doubles the switching frequency of the differential output waveform.
Signals on OUTP and OUTN are in the same phase when the input is zero, thus the current
is greatly reduced and the loss in the load is small. A tiny delay between OUTP and OUTN is
introduced to avoid high transient currents which could occur if both outputs switch
simultaneously.
TDA7493 can be used without a filter between the PWM output and the speaker since the
switching frequency of the output is beyond the audible range. The audio signal can be
recovered by the inherent inductance of the speaker and natural filter of the human ear.
Figure 6. Unipolar PWM output
The filterless configuration is usable in applications where the speaker connections to the
amplifier are shorter than 50 cm. In comparison to the low-pass Butterworth filter
configuration, the filterless configuration gives rise to higher EMI. This can be reduced, if
necessary, by inserting a ferrite bead filters close to the device.
Use a ferrite which exhibits high impedance at around 1 MHz and negligible impedance in
the audio band.
It is recommended to use an EMI filter if the speaker cable is longer than 50 cm.
Doc ID 14570 Rev 6
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