Output stage

TDA7374

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3.3

Other outstanding characteristics

3.3.1

Clipping detector output

The TDA7374 is equipped with an internal circuit able to detect the output stage saturation

providing a proper current sinking into a open collector output (pin 10) when a certain

distortion level is reached at each output.

This particular function allows gain compression facility whenever the amplifier is

overdriven, thus obtaining high quality sound at all listening levels.

Figure 18.

Clipping detection waveforms

3.3.2

Offset control

The quiescent output voltage must be as close as possible to its nominal value, so that less

undistorted power would be available.

For this reason an input bias current compensation is implemented to riduce the voltage

drop across the input resistors, which appears amplified at the outputs.

3.3.3

Gain internally fixed to 26 dB

Advantages of this design choice are in terms of:

●

components and space saving

●

output noise, supply voltage rejection and distortion optimization.

3.3.4

Silent turn on/off and muting/stand-by function

The stand-by can be easily activated by means of a CMOS level applied to pin 7 through a

RC filter.

Under stand-by condition the device is turned off completely (supply current = 1 µA typ.;

output attenuation = 90 dB typ.). Every ON/OFF operation is virtually pop free.

Furthermore, at turn-on the device stays in muting condition for a time determined by the

value assigned to the SVR capacitor (T= Csvr * 7,000).

While in muting the device outputs becomes insensitive to any kinds of signal that may be

present at the input terminals. In other words every transient coming from previous stages

produces no unpleasant acoustic effect to the speakers. Another situation under which the

device is totally muted is whenever the supply voltage drops lower than 7V. This is helpful to

pop suppression during the turn-off by battery switch.