TDA7575B Datasheet, PDF (28/32 Pages) STMicroelectronics – 2 x 75W multifunction dual-bridge power amplifier with integrated digital diagnostics

Diagnostics functional description
TDA7575B
Table 10. Double fault table for turn on diagnostic
S. GND (sc) S. GND (sk)
S. Vs
S. GND (sc)
S. GND
S. GND
S. Vs + S.
GND
S. GND (sk)
/
S. GND
S. Vs
S. Vs
/
/
S. Vs
S. Across L.
/
/
/
Open L.
/
/
/
S. Across L.
S. GND
S. GND
S. Vs
S. Across L.
/
Open L.
S. GND
Open L. (*)
S. Vs
N.A.
Open L. (*)
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 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.
To guarantee always resident functions, every kind of diagnostic cycles (Turn on,
Permanent, Offset) 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.
7.7
I²C 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: (STAND-BY OUT + DIAG ENABLE) --- 500 ms (min) --- MUTING OUT
– TURN-OFF: MUTING IN --- 20 ms --- (DIAG DISABLE + STAND-BY IN)
Car Radio Installation: DIAG ENABLE (write) --- 200ms --- I²C read (repeat until All faults
disappear).
– OFFSET TEST: Device in Play (no signal) --
– OFFSET ENABLE - 30ms - I²C reading
(repeat I²C reading until high-offset message disappears).
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