TDA7476

8/19

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

s

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 permanently to 0 level if one or both AUX outputs of

the car radio are unused.

Timing

s

From the byte "ADD1" to the byte "ADD2" the mP must wait a period Twait1(see Software Specification)

that is depending on the timing capacitor CT according to the following table (Twait1> tm, max):

Note: any (positive) spread of the capacitor value must be added. The relation to be used to determine Twait1

from the value of CT according to the following:

Twait1 > tm, max = (130 · CT/10

µF)ms

s

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:

Twait2 > ts, max = (140 · CT/10

µF)ms

For bridge or bridge equivalent devices (figg.5,6), Ct = 10

µF will be enough.

TURN-ON DIAGNOSTIC - THRESHOLDS

CH1, CH2, CH3, CH4, CH5

s

Output voltage during test. (The power amplifier must be in ST-BY mode).

s

Voltage across the load during test. (The power amplifier must be in ST-BY mode).

s

Note: some faults can mask others if they are present at the same moment on the same channel:

- If there is a short to GND and an open load on the same channel, the TDA7476 gives information only

about one of them, depending on the wire on which the short circuit is present.

- The short circuit to GND masks any short circuit across the load.

- The short circuit to Vs masks any short or open load.

CT (

µF)

tm max (ms)

3.3

45

4.7

65

10

130

22

290

47

620

100

1300

D96AU502B

S.C. to GND

x

S.C. to Vs

0V

1.2V

x

Normal Operation

0.8V

S.C. across Load

x

Open Load

0V

22mV

220mV

x

Normal Operation

5mV

550mV

D97AU631A