TDA7575B Datasheet, PDF (23/32 Pages) STMicroelectronics – 2 x 75W multifunction dual-bridge power amplifier with integrated digital diagnostics

TDA7575B
Diagnostics functional description
7
Diagnostics functional description
7.1
Turn-on diagnostic
It is activated at the turn-on (stand-by out) under I²C bus request. Detectable output faults are:
– SHORT TO GND
– SHORT TO Vs
– SHORT ACROSS THE SPEAKER
– OPEN SPEAKER
To verify if any of the above misconnections are in place, a subsonic (inaudible) current
pulse (Figure 29) is internally generated, sent through the speaker(s) and sunk back. The
Turn On diagnostic status is internally stored until a successive diagnostic pulse is
requested (after a I²C reading).
If the "stand-by out" and "diag. enable" commands are both given through a single
programming step, the pulse takes place first (power stage still in stand-by mode, low,
outputs = high impedance).
Afterwards, when the Amplifier is biased, the PERMANENT diagnostic takes place. The
previous Turn On state is kept until a short appears at the outputs.
Figure 29. Turn - on diagnostic: working principle
Vs~5V
Isource
CH+
CH-
I (mA)
Isource
Isink
Isink
~100mS
Measure time
t (ms)
Fig. Figure 30 and Figure 31 show SVR and OUTPUT waveforms at the turn-on (stand-by
out) with and without Turn-on diagnostic.
Figure 30. SVR and output behavior - case 1: without turn-on diagnostic
Vsvr
Out
Permanent diagnostic
acquisition time (100mS Typ)
Bias (power amp turn-on)
Diagnostic Enable
(Permanent)
FAULT
event
t
Read Data
I2CB DATA
Permanent Diagnostics data (output)
permitted time
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