TDA7561 Datasheet, PDF (10/19 Pages) STMicroelectronics – MULTIFUNCTION QUAD POWER AMPLIFIER WITH BUILT-IN DIAGNOSTICS FEATURES

TDA7561
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:
S.C. across Load x Normal Operation x
Open Load
0V
0.5Ω 1.5Ω
70Ω
130Ω
Infinite
D01AU1254
If the Line-Driver mode (Gv= 12 dB and Line Driver Mode diagnostic = 1) is selected, the same thresholds will
change as follows:
S.C. across Load x Normal Operation x
Open Load
0Ω
1.5Ω 4.5Ω
200Ω 400Ω
infinite
D01AU1252
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.
2) DIAGNOSTIC mode. It is enabled via I²C bus and self activates if an output overload (such to cause the in-
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
next one is activated by an I²C reading. This is to ensure continuous diagnostics throughout the car-radio op-
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).
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