11/20

TDA7564

– 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

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 19. Restart timing without Diagnostic Enable (Permanent) - Each 1mS time, a sampling of

the fault is done

Figure 20. Restart timing with Diagnostic Enable (Permanent)

OUTPUT DC OFFSET DETECTION

Any DC output offset exceeding ±2V are signalled out. This inconvenient might occur as a consequence of ini-

tially defective or aged and worn-out input capacitors feeding a DC component to the inputs, so putting the

speakers at risk of overheating.

This diagnostic has to be performed with low-level output AC signal (or Vin = 0).

The test is run with selectable time duration by microprocessor (from a "start" to a "stop" command):

– START = Last reading operation or setting IB1 - D5 - (OFFSET enable) to 1

– STOP = Actual reading operation

Excess offset is signalled out if persistent throughout the assigned testing time. This feature is disabled if any

overloads leading to activation of the short-circuit protection occurs in the process.

AC DIAGNOSTIC.

It is targeted at detecting accidental disconnection of tweeters in 2-way speaker and, more in general, presence

of capacitively (AC) coupled loads.

This diagnostic is based on the notion that the overall speaker's impedance (woofer + parallel tweeter) will tend

to increase towards high frequencies if the tweeter gets disconnected, because the remaining speaker (woofer)

would be out of its operating range (high impedance). The diagnostic decision is made according to peak output

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

circuit protection intervention

(i.e. short circuit to GND)

Short circuit removed

1-2mS

100/200mS

1mS

1mS