TDA7564

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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 con-

ditions and lower than 250mApk should the parallel tweeter be missing. The test has to last for a minimum num-

ber 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.

Fig. 21 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 21. Current detection: Load impedance magnitude |Z| vs. output peak voltage of the sinus

MULTIPLE FAULTS

When more misconnections are simultaneously in place at the audio outputs, it is guaranteed that at least one

provided that the diagnostic is enabled. This is true for both kinds of diagnostic (Turn on and Permanent).

The table below shows all the couples of double-fault possible. It should be taken into account that a short circuit

with the 4 ohm speaker unconnected is considered as double fault.

Double fault table for Turn On Diagnostic

S. GND (so)

S. GND (sk)

S. Vs

S. Across L.

Open L.

S. GND (so)

S. GND

S. GND

S. Vs + S. GND

S. GND

S. GND

S. GND (sk)

/

S. GND

S. Vs

S. GND

Open L. (*)

S. Vs

/

/

S. Vs

S. Vs

S. Vs

S. Across L.

/

/

/

S. Across L.

N.A.

Open L.

/

/

/

/

Open L. (*)

1234

5678

1

2

3

5

10

20

30

50

Vout (Peak)

Load |z| (Ohm)

Iout (peak) <250mA

Iout (peak) >500mA

Low current detection area

(Open load)

D5 = 1 of the DBx byres

High current detection area

(Normal load)

D5 = 0 of the DBx bytes