General structure

STA540SA

20/30

Doc ID 16066 Rev 2

8.7

Built-in short-circuit protection

Reliable and safe operation in the presence of all kinds of short circuits involving the outputs

is assured by built-in protection. Additionally, a soft short-condition is signalled out (to the

AC/DC short circuit to GND, to VS, and across the speaker) during the turn-on phase to

ensure correct operation of the device and the speakers.

This particular kind of protection acts in such a way as to prevent the device being turned on

(by ST_BY) when a resistive path (less than 16

Ω) is present between the output and GND.

It is important to have the external current source driving the ST_BY pin limited to 5 mA.

This is because the associated circuitry is normally disabled with currents >5 mA.

This extra function becomes particularly attractive when, in the single-ended configuration,

one capacitor is shared between two outputs as shown in Figure 29.

Figure 29.

Sharing a capacitor

If the output capacitor Cout is shorted for any reason, the loudspeaker is not damaged.

8.7.1

Diagnostic facilities (pin 12)

The STA540SA is equipped with diagnostic circuitry that is able to detect the following

events:

Clipping in the output signal

Thermal shutdown

Output fault:

–

short to GND

–

short to VS

–

soft short at turn on

The information is available across an open collector output (pin 12) through a current

sinking when the event is detected.

Figure 30.

Clipping detection waveforms

A current sinking at pin 12 is provided when a certain distortion level is reached at each

output. This function initiates a gain-compression facility whenever the amplifier is

overdriven.

Obsolete

Product(s)

- Obsolete

Product(s)