TDA7566

Diagnostics functional description

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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 22.

Restart timing without Diagnostic Enable (Permanent)

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

Figure 23.

Restart timing with Diagnostic Enable (Permanent)

4.3

Output DC offset detection

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

consequence of initially 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.

4.4

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

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