TDA7561

10/19

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:

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

change as follows:

b) 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

The TDA7561 has 2 operating statuses:

1) RESTART mode. The diagnostic is not enabled. Each audio channel operates independently from each oth-

er. 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 (fig. 17). Restart takes place when the overload is removed.

tervention of the short-circuit protection) occurs to the speakers outputs . Once activated, the diagnostics pro-

cedure develops as follows (fig. 18):

- 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 chan-

nel 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

erating time.

- To check the status of the device a sampling system is needed. The timing is chosen at microprocessor level

(over half a second is recommended).

S.C. across Load

x

Open Load

0V

1.5

Ω

70

Ω

Infinite

x

Normal Operation

0.5

Ω

130

Ω

D01AU1254

D01AU1252

S.C. across Load

x

Open Load

0

Ω

4.5

Ω

200

Ω

infinite

x

Normal Operation

1.5

Ω

400

Ω