STA543SA

5 General structure

CD00061065

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5

General structure

5.1

Gain Internally Fixed to 20dB in Single Ended, 26dB in Bridge

Advantages of this design choice are in terms of:

●

components and space saving

●

output noise, supply voltage rejection and distortion optimization.

5.2

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 9 through a RC

filter.

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

attenuation= 80dB min.).

Every ON/OFF operation is virtually pop free. Furthemore, at turn-on the device stays in muting

condition for a time determined by the value assigned to the SVR capacitor. 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

unplesantacoustic effect to the speakers.

5.3

STAND-BY DRIVING (pin9)

Some precautions have to be taken in the definition of stand-by driving networks: pin 9 cannot

be directly driven by a voltage source whose curent capability is higher than 5mA. In pratical

cases a series resistance has always to be inserted, having it the double purpose of limiting the

current at pin 9 and to smooth down the stand-by ON/OFF transitions - in combination with a

capacitor - for output pop prevention.

In any case, a capacitor of at lest 100nF from pin 9 to S-GND, with no resistance in between, is

necessary to ensure correct turn-on.

5.4

Output Stage

The fully complementary output stage was made possible by the development of a new

component: the ST exclusive power ICV PNP.

A novel design based upon the connection shown in

Figure 9. has then allowed the full

exploitation of its possibilities.

The clear advantages this new approach has over classical output stages are as follows:

5.5

Rail-to-Rail Output Voltage Swing With No Need of Bootstrap

Capacitors.

0.3