Diagnostics functional description

TDA7566

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Concerning SHORT ACROSS THE SPEAKER / OPEN SPEAKER, the threshold varies

from 26 dB to 12 dB gain setting, since different loads are expected (either normal speaker's

impedance or high impedance). The values in case of 26 dB gain are as follows:

Figure 20.

Thresholds for SHORT ACROSS THE SPEAKER/OPEN SPEAKER

If the Line-Driver mode (Gv= 12 dB and Line Driver Mode diagnostic = 1) is selected, the

same thresholds will change as follows:

Figure 21.

Thresholds for Line-Drivers

4.2

Permanent diagnostics

Detectable conventional faults are:

–

SHORT TO GND

–SHORT TO Vs

–

SHORT ACROSS THE SPEAKER

The following additional features are provided:

–

OUTPUT OFFSET DETECTION

–

AC DIAGNOSTIC

The TDA7566 has 2 operating statuses:

1.

RESTART mode. The diagnostic is not enabled. Each audio channel operates

independently from each other. If any of the a.m. faults occurs, only the channel(s)

interested is shut down. A check of the output status is made every 1 ms (Figure 22).

Restart takes place when the overload is removed.

2.

(such to cause the intervention of the short-circuit protection) occurs to the speakers

outputs . Once activated, the diagnostics procedure develops as follows (Figure 23):

–

To avoid momentary re-circulation spikes from giving erroneous diagnostics, a

check of the output status is made after 1ms: if normal situation (no overloads) is

detected, the diagnostic is not performed and the channel returns back active.

–

Instead, if an overload is detected during the check after 1 ms, then a diagnostic

cycle having a duration of about 100 ms is started.

–

After a diagnostic cycle, the audio channel interested by the fault is switched to

RESTART mode. The relevant data are stored inside the device and can be read

by the microprocessor. When one cycle has terminated, the next one is activated

S.C. across Load

x

Open Load

0V

1.75

Ω

45

Ω

Infinite

x

Normal Operation

0.5

Ω

85

Ω

D01AU1327

D02AU1340

S.C. across Load

x

Open Load

0

Ω

7

Ω

180

Ω

infinite

x

Normal Operation

2

Ω

330

Ω