TDA7575PD datasheet(15/17 Pages) STMICROELECTRONICS

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TDA7575PD

MULTIPLE FAULTS.

When more misconnections are simultaneously in place at the audio outputs, it is guaranteed that at least one

of them is initially read out. The others are notified after successive cycles of I2C reading and faults removal,

provided that the diagnostic is enabled. This is true for both kinds of diagnostic (Turn on and Permanent).

The table below shows all the couples of double-fault possible. It should be taken into account that a short circuit

with the 4 ohm speaker unconnected is considered as double fault.

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 recognisable 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).

FAULTS AVAILABILITY

All the results coming from I2Cbus, 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.

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: (STAND-BY OUT + DIAG ENABLE) --- 500 ms (min) --- MUTING OUT

– TURN-OFF: MUTING IN --- 20 ms --- (DIAG DISABLE + STAND-BY IN)

Car Radio Installation: DIAG ENABLE (write) --- 200 ms --- I2C read (repeat until All faults disappear).

– OFFSET TEST: Device in Play (no signal) --

– OFFSET ENABLE - 30ms - 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. Vs + S. GND

S. GND

S. GND (sk)

S. GND

S. Vs

S. GND

Open L. (*)

S. Vs

S. Across L.

///

S. Across L.

N.A.

Open L.

////

Open L. (*)

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