Application hints

TDA7381

8/13

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 k

Ω. 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.

Figure 7.

Diagnostics circuit

+

-

0.1

μF

C1 ÷ C4

8K

Ω

8K

Ω

400

Ω

400

Ω

100K

Ω

100K

Ω

70K

Ω

IN

D95AU302

TOWARDS

OTHER CHANNELS

10K

Ω

10K

Ω

47

μF

C6

0.1

μF

C5

SVR

AC_GND

VREF

R

Vpin 25

25

D95AU303

TDA7385