13/19

TDA7476

READ BYTE 1

READ BYTE 2

READ BYTE 3

Repetitive turn-on diagnostic

During the turn-on diagnostic, the TDA7476 can reveal false "short circuit across load" and/or false "open load"

due to noise sources such as door slams.

This problem can be solved doing more than one turn-on diagnostic routine. If the

µP asks for N times the state

of the audio system, it has to consider a fault as really present only if it is detected in all the N turn-on diagnos-

tic.As above explained, the first time the TDA7476 receivers the byte ADD1, it does the turn-on diagnostic; then

each time it is addessed with ADD1, it does the permanent diagnostic. This is not true if, when the

µP sends for

the first time the byte ADD2, it does not send to the TDA7476 the acknowledge after it has received the byte

BYTE3. In this case, the TDA7476 does not switch from turn-on to permanent diagnostic mode so if it receives

again the byte ADD1 it works as it was the first time that it does the turn-on diagnostic. In order to do repetitive

turn-on diagnostic, the mP has to be programmed as following:

s

Step 1: the

µP sends ADD1

s

Step 2: the

µP waits Twait1 seconds

s

Step 3: the

µP sends ADD2, receives BYTE1, BYTE2, BYTE3, does not send the acknowlegde after

BYTE3

MSB

LSB

STATUS

D7

D6

D5

D4

D3

D2

D1

D0

0

0

X

X

1

1

X

0

CH1 short circuit to Vs

0

0

X

X

1

1

0

X

CH1 short circuit to GND

00

X

X

1

111

00

X

X

1

111

0

0

X

0

1

1

X

X

CH2 short circuit to Vs

0

0

0

X

1

1

X

X

CH2 short circuit to GND

00

111

1

X

X

00

111

1

X

X

1

1

X

X

1

1

X

0

CH3 short circuit to Vs

1

1

X

X

1

1

0

X

CH3 short circuit to GND

11

X

X

1

111

11

X

X

1

111

1

1

X

0

1

1

X

X

CH4 short circuit to Vs

1

1

0

X

1

1

X

X

CH4 short circuit to GND

11

111

1

X

X

11

111

1

X

X

1

1

X

X

X

X

1

0

AUX1 short circuit to GND

1

1

X

X

X

X

0

1

AUX1 open load

1

1

X

X

1

0

X

X

AUX2 short circuit to GND

1

1

X

X

0

1

X

X

AUX2 open load

1

1

X

0

X

X

X

X

CH5 short circuit to Vs

1

1

0

X

X

X

X

X

CH5 short circuit to GND

11

11

X

X

X

X

11

11

X

X

X

X

START

ADD1

ACK

ACK