TDA7476_01 Datasheet, PDF (8/19 Pages) STMicroelectronics – CAR RADIO DIAGNOSTIC PROCESSOR

TDA7476
Permanent diagnostic - AUX1, AUX2 - Short circuit to GND and open load
s The detection mode of the auxiliary inputs is equal to what is in place during turn-on, but the fault must
be lasting without interruption for more than 2 seconds.The warning pin is pulled down only in case of
short to GND. This is to avoid that this pin remains permanently to 0 level if one or both AUX outputs of
the car radio are unused.
Timing
s From the byte "ADD1" to the byte "ADD2" the mP must wait a period Twait1(see Software Specification)
that is depending on the timing capacitor CT according to the following table (Twait1> tm, max):
CT (µF)
tm max (ms)
3.3
45
4.7
65
10
130
22
290
47
620
100
1300
Note: any (positive) spread of the capacitor value must be added. The relation to be used to determine Twait1
from the value of CT according to the following:
Twait1 > tm, max = (130 · CT/10µF)ms
s After the byte "ADD2" the power amplifier can be switched-on. In some cases, the µP has to wait until
the current pulse is finished (Twait2). This time (ts in fig.1) is given by:
Twait2 > ts, max = (140 · CT/10µF)ms
For bridge or bridge equivalent devices (figg.5,6), Ct = 10µF will be enough.
TURN-ON DIAGNOSTIC - THRESHOLDS
CH1, CH2, CH3, CH4, CH5
s Output voltage during test. (The power amplifier must be in ST-BY mode).
S.C. to GND x Normal Operation x
S.C. to Vs
0V
0.8V 1.2V
V_S-1.2 V_S-0.6V
V_S
D96AU502B
s Voltage across the load during test. (The power amplifier must be in ST-BY mode).
S.C. across Load x Normal Operation x
Open Load
0V
5mV 22mV
220mV 550mV
V_S
D97AU631A
s Note: some faults can mask others if they are present at the same moment on the same channel:
- If there is a short to GND and an open load on the same channel, the TDA7476 gives information only
about one of them, depending on the wire on which the short circuit is present.
- The short circuit to GND masks any short circuit across the load.
- The short circuit to Vs masks any short or open load.
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