TDA7566_06 Datasheet, PDF (16/28 Pages) STMicroelectronics – 4x40W multifunction quad power amplifier with built-in diagnostics features

Diagnostics functional description
TDA7566
disconnected, because the remaining speaker (woofer) would be out of its operating range
(high impedance). The diagnostic decision is made according to peak output current
thresholds, as follows:
Iout > 500mApk = NORMAL STATUS
Iout < 250mApk = OPEN TWEETER
To correctly implement this feature, it is necessary to briefly provide a signal tone (with the
amplifier in "play") whose frequency and magnitude are such to determine an output current
higher than 500mApk in normal conditions and lower than 250mApk should the parallel
tweeter be missing. The test has to last for a minimum number of 3 sine cycles starting from
the activation of the AC diagnostic function IB2<D2>) up to the I²C reading of the results
(measuring period). To confirm presence of tweeter, it is necessary to find at least 3 current
pulses over 500mA over all the measuring period, else an "open tweeter" message will be
issued.
The frequency / magnitude setting of the test tone depends on the impedance
characteristics of each specific speaker being used, with or without the tweeter connected
(to be calculated case by case). High-frequency tones (> 10 KHz) or even ultrasonic signals
are recommended for their negligible acoustic impact and also to maximize the impedance
module's ratio between with tweeter-on and tweeter-off.
Figure 24 shows the Load Impedance as a function of the peak output voltage and the
relevant diagnostic fields.
This feature is disabled if any overloads leading to activation of the short-circuit protection
occurs in the process.
Figure 24. Current detection: Load impedance magnitude |Z| Vs. output peak voltage of
the sinus
Load |z| (Ohm)
50
Low current detection area
30
(Open load)
20
D5 = 1 of the DBx byres
Iout (peak) <250mA
Iout (peak) >500mA
10
High current detection area
5
(Normal load)
D5 = 0 of the DBx bytes
3
2
1
1
2
3
4
5
6
7
8
Vout (Peak)
4.5
Multiple faults
When more misconnections are simultaneously in place at the audio outputs, it is
guaranteed that at least one of them is initially read out. The others are notified after
successive cycles of I²C reading and faults removal, provided that the diagnostic is enabled.
This is true for both kinds of diagnostic (Turn on and Permanent).
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