TDA7381_08 Datasheet, PDF (9/13 Pages) STMicroelectronics – 4 x 25W quad bridge car radio amplifier

TDA7381
Figure 8. Clipping detection waveforms.
Application hints
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
ST-BY PIN
VOLTAGE
t
MUTE PIN
VOLTAGE
t
Vs
OUTPUT
WAVEFORM
t
Vpin 25
WAVEFORM
D95AU304
t
CLIPPING
SHORT TO GND THERMAL
OR TO Vs
PROXIMITY
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