Diagnostics functional description

TDA7575B

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Doc ID 14103 Rev 3

Table 10.

Double fault table for turn-on diagnostic

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: (Standby OUT + DIAG enable) --- 500 ms (min) --- muting OUT

●

Turn-off: Muting IN --- 20 ms --- (DIAG disable + standby IN)

Car radio installation: DIAG enable (write) --- 20 0ms --- I2C read (repeat until all faults

disappear).

–

Offset test: device in play (no signal)

–

Offset enable - 30 ms - I2C reading

(repeat I2C reading until high-offset message disappears).

S. GND (sc)

S. GND (sk)

S. Vs

S. Across L.

Open L.

S. GND (sc)

S. GND

S. GND

S. Vs + S.

GND

S. GND

S. GND

S. GND (sk)

/

S. GND

S. Vs

S. GND

Open L. (*)

S. Vs

/

/

S. Vs

S. Vs

S. Vs

S. Across L.

/

/

/

S. Across L.

N.A.

Open L.

/

/

/

/

Open L. (*)