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 (G
v
= 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 I
2
C 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 1.65Ω
45Ω
Infinite
xNormal Operation
0.5Ω
85Ω
AC00566
D02AU1340
S.C. across Load x Open Load
0Ω 7Ω 180Ω infinite
xNormal Operation
2Ω 330Ω
