Diagnostics functional description

TDA7566

14/29

Doc ID 9801 Rev 6

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.

Diagnostic mode. It is enabled via I2C bus and self activates if an output overload (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 by

S.C. across Load

x

Open Load

0V

1.65

Ω

45

Ω

Infinite

x

Normal Operation

0.5

Ω

85

Ω

AC00566

D02AU1340

S.C. across Load

x

Open Load

0

Ω

7

Ω

180

Ω

infinite

x

Normal Operation

2

Ω

330

Ω