Diagnostics functional description

TDA7561

12/27

Doc ID 8326 Rev 6

4

Diagnostics functional description

4.1

Turn-on diagnostic

It is activated at the turn-on (standby out) under I2C bus request. Detectable output faults

are:

●

Short to GND

●

Short to Vs

●

Short across the speaker

●

Open speaker

To verify if any of the above misconnections are in place, a subsonic (inaudible) current

pulse (Figure 16) is internally generated, sent through the speaker(s) and sunk back.The

Turn On diagnostic status is internally stored until a successive diagnostic pulse is

requested (after a I2C reading).

If the "standby out" and "diag. enable" commands are both given through a single

programming step, the pulse takes place first (power stage still in stand-by mode, low,

outputs = high impedance).

Afterwards, when the Amplifier is biased, the permanent diagnostic takes place. The

previous Turn-on state is kept until a short appears at the outputs.

Figure 16.

Turn-on diagnostic: working principle

Figure 17 and 18 show SVR and output waveforms at the turn-on (stand-by out) with and

without turn-on diagnostic.

Figure 17.

SVR and output behaviour (case 1: without turn-on diagnostic)