TDA7493

Applications information

Doc ID 14570 Rev 6

13/30

5.4

Filterless modulation

The modulation scheme of BTL is called unipolar PWM output. The differential output

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.