TDA7575B datasheet(28/32 Pages) STMICROELECTRONICS

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Diagnostics functional description

TDA7575B

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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: (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) --- 200ms --- 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.

N.A.

Open L.

Open L. (*)

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