TDA7566 datasheet(17/28 Pages) STMICROELECTRONICS

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TDA7566

Diagnostics functional description

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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.

S. GND (so) / S. GND (sk) in the above table make a distinction according to which of the 2

outputs is shorted to ground (test-current source side= so, test-current sink side = sk). More

precisely, in channels LF and LR, so = CH+, sk = CH-; in channels LR and RF, so = CH-, SK

= CH+.

In Permanent Diagnostic the table is the same, with only a difference concerning Open Load

(*), which is not among the recognisable faults. Should an Open Load be present during the

device's normal working, it would be detected at a subsequent Turn on Diagnostic cycle (i.e.

at the successive Car Radio Turn on).

4.6

Faults availability

All the results coming from I2Cbus, by read operations, are the consequence of

measurements inside a defined period of time. If the fault is stable throughout the whole

period, it will be sent out. This is true for DC diagnostic (Turn on and Permanent), for Offset

Detector, for AC Diagnostic (the low current sensor needs to be stable to confirm the Open

tweeter).

To guarantee always resident functions, every kind of diagnostic cycles (Turn on,

Permanent, Offset, AC) will be reactivate after any I2C reading operation. So, when the

micro reads the I2C, a new cycle will be able to start, but the read data will come from the

previous diag. cycle (i.e. The device is in Turn On state, with a short to Gnd, then the short is

removed and micro reads I2C. The short to Gnd is still present in bytes, because it is the

result of the previous cycle. If another I2C reading operation occurs, the bytes do not show

the short). In general to observe a change in Diagnostic bytes, two I2C reading operations

are necessary.

4.7

I2C Programming/reading sequence

A correct turn on/off sequence respectful of the diagnostic timings and producing no audible

noises could be as follows (after battery connection):

TURN-ON: (STAND-BY OUT + DIAG ENABLE) --- 500 ms (min) --- MUTING OUT

TURN-OFF: MUTING IN --- 20 ms --- (DIAG DISABLE + STAND-BY IN)

Table 4.

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. Vs + S.

GND

S. GND

S. GND (sk)

S. GND

S. Vs

S. GND

Open L. (*)

S. Vs

S. Across L.

N.A.

Open L.

Open L. (*)

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