General structure

STA540SAN

20/26

Doc ID 18306 Rev 1

8.7

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 28.

Figure 28.

Sharing a capacitor

8.7.1

Diagnostic facilities (pin 10)

The STA540SAN 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 10) through a current

sinking when the event is detected.

Figure 29.

Clipping detection waveforms

A current sinking at pin 10 is provided when a certain distortion level is reached at each

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

overdriven.