TDA7381_08 Datasheet, PDF (8/13 Pages) STMicroelectronics – 4 x 25W quad bridge car radio amplifier

Application hints
TDA7381
3.4
Diagnostics facility
The TDA7381 is equipped with a diagnostics circuitry able to detect the following events:
● Clipping in the output stage
● Overheating (thermal shut-down proximity)
● Output misconnections (OUT-GND and OUT-Vs shorts)
Diagnostics information is available across an open collector output located at pin 25 (fig. 8)
through a current sinking whenever at least one of the above events is recognized.
Among them, the Clipping detector acts in a way to output a signal as soon as one or more
power transistors start being saturated.
As a result, the clipping-related signal at pin 25 takes the form of pulses, which are perfectly
syncronized with each single clipping event in the music program and reflect the same
duration time (Figure 8).
Applications making use of this facility usually operate a filtering/integration of the pulses
train through passive R-C networks and realize a volume (or tone bass) stepping down in
association with microprocessor-driven audioprocessors.
The maximum load that pin 25 can sustain is 1 kΩ. Due to its operating principles, the
clipping detector has to be viewed mainly as a power-dependent feature rather than
frequency-dependent. This means that clipping state will be immediately signaled out
whenever a fixed power level is reached, regardless of the audio frequency.
Figure 6. Input/output biasing.
100KΩ
0.1μF
C1 ÷ C4
IN
+
-
8KΩ
400Ω
V_S
10KΩ
70KΩ _SVR
10KΩ
100KΩ
47μF
C6
400Ω
8KΩ
-
AC_GND ₊
0.1μF
C5
D95AU302
TOWARDS
OTHER CHANNELS
Figure 7. Diagnostics circuit
25
R
Vpin 25
VREF
TDA7385
D95AU303
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