TDA7577BLVPD datasheet(19/43 Pages) STMICROELECTRONICS

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TDA7577BLV

Diagnostics functional description

4.2

Permanent diagnostics

Detectable conventional faults are:



SHORT TO GND



SHORT TO Vs



SHORT ACROSS THE SPEAKER

The following additional feature is provided:



OUTPUT OFFSET DETECTION

The TDA7577BLV has 2 operating status:

RESTART mode. The diagnostic is not enabled. Each audio channel operates

independently of each other. If any of the a.m. faults occurs, only the channel(s)

interested is shut down. A check of the output status is made every 1 ms (Figure 29).

Restart takes place when the overload is removed.

DIAGNOSTIC mode. It is enabled via I2C bus and it self activates if an output overload

(such as to cause the intervention of the short-circuit protection) occurs to the speakers

outputs. Once activated, the diagnostics procedure develops as follows (Figure 30):

–

To avoid momentary re-circulation spikes from giving erroneous diagnostics, a

check of the output status is made after 1ms: if normal situation (no overloads) is

detected, the diagnostic is not performed and the channel returns active.

–

Instead, if an overload is detected during the check after 1 ms, then a diagnostic

cycle having a duration of about 100 ms is started.

–

After a diagnostic cycle, the audio channel interested by the fault is switched to

RESTART mode. The relevant data are stored inside the device and can be read

by the microprocessor. When one cycle has terminated, the next one is activated

by an I2C reading. This is to ensure continuous diagnostics throughout the car-

radio operating time.

–

To check the status of the device a sampling system is needed. The timing is

chosen at microprocessor level (more than half a second is recommended).

Figure 29. Restart timing without diagnostic enable (permanent) each 1ms time, a

sampling of the fault is done

Figure 30. Restart timing with diagnostic enable (permanent)

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