TDA7381

Application hints

9/13

Figure 8.

Clipping detection waveforms.

In other words, this feature offers the means to counteract the extremely sound-damaging

effects of clipping, caused by a sudden increase of odd order harmonics and appearance of

serious intermodulation phenomena. Another possible kind of distortion control could be the

setting of a maximum allowable THD limit (e.g. 0.5%) over the entire audio frequency range.

Besides offering no practical advantages, this procedure cannot be much accurate, as the

non-clipping distortion is likely to vary over frequency.

In case of overheating, pin 25 will signal out the junction temperature proximity to the

thermal shut-down threshold. This will typically start about 2°C before the thermal shut-

down threshold is reached.

As various kind of diagnostics information is available at pin 25 (clipping, shorts and

overheating), it may be necessary to operate some distinctions on order to treat each event

separately.

This could be achieved by taking into account the intrinsically different timing of the

diagnostics output under each circumstance. In fact, clipping will produce pulses normally

much shorter than those present under faulty conditions.

An example of circuit able to distinguish between the two occurrences is shown by

Figure 10.

Figure 9.

Diagnostics waveforms

t

t

t

MUTE PIN

VOLTAGE

Vs

OUTPUT

WAVEFORM

Vpin 25

WAVEFORM

SHORT TO GND

OR TO Vs

D95AU304

CLIPPING

THERMAL

PROXIMITY

ST-BY PIN

VOLTAGE

t