TDA7566

Diagnostics functional description

Doc ID 9801 Rev 6

17/29

4.5

Multiple faults

When more misconnections are simultaneously in place at the audio outputs, it is

guaranteed that at least one of them is initially read out. The others are notified after

successive cycles of I2C reading and faults removal, 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.

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 recognizable 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 I2C bus, 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.

Table 5.

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. (*)