Diagnostics functional description TDA7575B
28/32 Doc ID 14103 Rev 3
Table 10. Double fault table for turn-on diagnostic
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 both the channels SO = CH+, and 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).
7.6 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.
To guarantee always resident functions, every kind of diagnostic cycles (turn-on, permanent,
offset) 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.
7.7 I
2
C programming/reading sequences
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: (Standby OUT + DIAG enable) --- 500 ms (min) --- muting OUT
● Turn-off: Muting IN --- 20 ms --- (DIAG disable + standby IN)
Car radio installation: DIAG enable (write) --- 20 0ms --- I
2
C read (repeat until all faults
disappear).
– Offset test: device in play (no signal)
– Offset enable - 30 ms - I
2
C reading
(repeat I
2
C reading until high-offset message disappears).
S. GND (sc) S. GND (sk) S. Vs S. Across L. Open L.
S. GND (sc) 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. (*)
