TDA7476 Datasheet, PDF (12/15 Pages) STMicroelectronics – CAR RADIO DIAGNOSTIC PROCESSOR

TDA7476
In this way only after that the TDA7476 has done for N times the turn-on diagnostic, it switches from
turn-on to permanent diagnostic mode.
From now the TDA7476 always does the permanent diagnostic.
To save time when the audio system is switched on, it is possible to do the repetitive turn-on diagnostic
when the car-radio is turned off. In this case the steps to follow to do the repetitive turn-on diagnostic are
the following:
1- to switch off the TDA7476 connecting STBY pin to ground;
2- to wait T5V seconds(time necessaryfor the discharge of the capacitor). If C5V = 10µF then T5V = 20ms typ;
3- to switch on the TDA7476
4- to do the repetitive turn-on diagnostic as above described;
5- to turn off the TDA7476.
WARNING PIN
This is an open drain output pin that is activated when a fault condition is present for more than 2 sec
(TYP). The fault conditions related to the warning pin are as follows:
- AUX1, AUX2
Short to GND
- CH1, CH2, CH3, CH4, CH5:
Short Circuit to GND
Short Circuit to Vs
The purpose of this pin is to alert the µP and start with the permanent diagnostic routine only if faults
are present, thus avoiding CPU’s waste of time.
APPLICATION NOTES
On single-ended devices as in figure 6, 7 if the loads are present then both in turn-on and in perma-
nent diagnostic the fault present on one channel is pointed out for all the loads connected together.
For example:
- see fig.6 if CH1+ is shorted to ground, the TDA7476 reveals a short to groundboth for CH2 and for CH1.
- seefig.7 if CH1+ is shortedto ground, theTDA7476detectsa short circuit to groundfor CH1, CH2, CH3, CH4.
To use the TDA7476 with a car-radio system which has less than five audio channel and less than
two auxiliary loads, it is necessary to take some cares:
- If the loads are 4Ω speakers (Rcs= 3.3 KΩ), R ≅ 10Ω has to be connected between CH+ and CH- of
each channel (see figg. 5,6,7,8 concerning CH5). R ≅ 5Ω has to be used if loads are 2Ω speakers
(Rcs= 1.8 KΩ).
- If AUX1/AUX2 are unused, Rsens1/Rsens2 will not be needed. The AUX-IN pin(s) can be tied to the
5 internal regulator (pin 10) while setting the AUX-OUT pin(s) about 250mV lower than AUX-IN’s
(admissible range = 125mV to 500mV). This can easily be obtained by means of a voltage divider.
If both the AUX channelsare unused, pins 7-8 (AUX-INs) and pins 6-9 (AUX-OUTs) can be respectively
connectedtogether, so that a single voltage divider could be used.
The above actions will prevent any ”warning” activation which might cause unwanted microprocessor’s
interrupt.
12/15