TDA7566

10/19

b) 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

- AC DIAGNOSTIC

The TDA7566 has 2 operating statuses:

1 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 (fig. 17). Restart takes place when the overload is removed.

2 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 di-

agnostics procedure develops as follows (fig. 18):

– 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 per-

formed and the channel returns back active.

– Instead, if an overload is detected during the check after 1 ms, then a diagnostic cycle having a du-

ration 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 microproces-

sor level (over half a second is recommended).

Figure 17. Restart timing without Diagnostic Enable (Permanent)

Each 1ms time, a sampling of the fault is done

Figure 18. Restart timing with Diagnostic Enable (Permanent)

t

1-2mS

1mS

1mS

1mS

1mS

Overcurrent and short

circuit protection intervention

(i.e. short circuit to GND)

Short circuit removed

Out

t

Overcurrent and short

(i.e. short circuit to GND)

Short circuit removed

1mS

100mS

1mS

1mS