TDA7564B datasheet(16/34 Pages) STMICROELECTRONICS

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Diagnostics functional description

TDA7564B

16/34

4.2

Permanent diagnostics

Detectable conventional faults are:

–

Short to gnd

–Short to VS

–

Short across the speaker

The following additional features are provided:

–

Output offset detection

The TDA7564B has 2 operating statuses:

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

independently from 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 25).

Restart takes place when the overload is removed.

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

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

outputs. Once activated, the diagnostics procedure develops as follows (Figure 26):

–

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 back 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 (over half a second is recommended).

Figure 25. Restart timing without diagnostic enable (permanent) - Each 1mS time, a

sampling of the fault is done

Figure 26. Restart timing with diagnostic enable (permanent)

1-2mS

1mS

Overcurrent and short

circuit protection intervention

(i.e. short circuit to GND)

Short circuit removed

Out

Overcurrent and short

circuit protection intervention

(i.e. short circuit to GND)

Short circuit removed

1-2mS

100/200mS

1mS

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