Turn-on diagnostic - AUX1, AUX2

To detect if there is a short circuit to GND or an open load involving to the AUX output of the car radio,

the voltage across a sensing resistor Rsens is detected.

These output voltages (for example for the active antenna and for the booster) are usually generated

by high side drivers, but also voltage regulators with Vout > 5V are admissible.

The detection ranges can be set by adjusting the sensing resistors Rsens1 or Rsens2.

For example, if Rsens = 5Ohm, the following detection table will be operative (I = Vthr/Rsens):

Open Load

x

S.C. to GND

100mA

25mA

x

Normal Operation

150mA

17mA

D96AU503

Permanent diagnostic - CH1, CH2, CH3, CH4, CH5 - Short to GND and Vs

During the CAR-RADIO normal operation, to detect a short circuit to GND (or to Vs), the output volt-

ages are sensed. If one or more outputs stay at any voltage below 0.8V or over Vs-0.8V for more than

2 sec. (typ), the warning pin is pulled down.

The

µP can address the TDA7476 to know the status.

The subsonic current pulse is activated also in this case. The fault is correctly detected if it remains

until the memorization (tm in fig.1).

In this phase, faults regarding shorts across the load and open loads cannot be detected.

For single-ended devices as in fig. 5, 6 a short citcuit to ground is detected both when a short to

ground is really present and when the load is missing.

Permanent diagnostic - AUX1, AUX2 - Short circuit to GND and open load

The detection mode of the auxiliary inputs is equal to what is in place during turn-on, but the fault

must be lasting without interruption for more than 2 seconds.

The warning pin is pulled down only in case of short to GND. This is to avoid that this pin remains per-

manently to 0 level if one or both AUX outputs of the car radio are unused.

Timing

From the byte ”ADD1” to the byte ”ADD2” the

µP must wait a period Twait1(see Software Specifica-

µF)

3.3

45

4.7

65

10

130

22

290

47

620

100

1300

Note: any (positive) spread of the capacitor value must be added. The relation to be used to determine

µF)ms

After the byte ”ADD2” the power amplifier can be switched-on. In some cases, the

µP has to wait until

the current pulse is finished (Twait2). This time (ts in fig.1) is given by:

µF)ms

For bridge or bridge equivalent devices (figg.7,8), Cs = 10

µF will be enough.

For the TDA7375, connected as in fig.5, Cs = 47

µF if Cout = 1000µF, and Cs = 100µF if Cout = 2200µF.

If the circuit is as shown by fig. 6, the suggested values of Cs are as follows: Cs = 22

µF if Cout =

1000

µF, Cs = 47µF if Cout = 2200µF.

TDA7476

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