TDA7577BLVPD datasheet(22/43 Pages) STMICROELECTRONICS

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Diagnostics functional description

TDA7577BLV

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DocID025375 Rev 5

4.5

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 Ω speaker unconnected is considered as double fault.

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).

4.6

Fault presence information availability on I2C

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 reactivated after any I2C reading operation. Each I2C read-out

done by the microcontroller will enable a new diagnostic cycle, but the read data will come

from the previous diagnostic 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.

Table 5. Double fault table for turn on diagnostic

S. GND

S. Vs

S. Across L.

Open L.

S. GND

S. Vs + S. GND

S. GND

S. Vs

S. Across L.

N.A.

Open L.

Open L. (*)

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