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 I
2
C 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 I
2
C 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 I
2
C reading operation. So, when the
micro reads the I
2
C, 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 I
2
C. The short to GND is still present in bytes, because it is the
result of the previous cycle. If another I
2
C reading operation occurs, the bytes do not show
the short). In general to observe a change in Diagnostic bytes, two I
2
C 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. (*)
