TDA7476 查看數據表（PDF） - STMicroelectronics

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TDA7476

CAR RADIO DIAGNOSTIC PROCESSOR

STMicroelectronics 

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

VS-1.2 VS-0.6V

VS

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

VS

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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