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driven by a voltage source whose current capability is higher than 5mA. In practical cases a series resis-

tance has always to be inserted, having it the double purpose of limiting the current at pin 7 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 least 100nF from pin 7 to S-GND, with no resistance in between, is necessary

to ensure correct turn-on.

5.6 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 fig. 23 has then allowed the full exploitation of its pos-

sibilities. The clear advantagesthis new approach has over classical output stages are as follows:

5.6.1 Rail-to-Rail Output Voltage Swing With No Need of Bootstrap Capacitors.

each. Classical solutions adopting composite PNP-NPN for the upper output stage have higher saturation

loss on the top side of the waveform.

This unbalanced saturation causes a significant power reduction. The only way to recover power consists

of the addition of expensive bootstrap capacitors.

5.6.2 Absolute Stability Without Any External Compensation.

By controlling the amount of this local feedbackit is possible to force the loop gain (A*

) to less than unity

at frequency for which the phase shift is 180°. This means that the output buffer is intrinsically stableand

not prone to oscillation.

Most remarkably, the above feature has been achieved in spite of the very low closed loop gain of the

amplifier. In contrast, with the classical PNP-NPN stage, the solution adopted for reducing the gain at high

frequencies makes use of external RC networks, namely the Boucherot cells.

5.7 BUILT–IN SHORTCIRCUIT PROTECTION

Figure 23. The New Output Stage

Reliable and safe operation, in presence of all kinds of short circuit involving the outputs is assured by

SHORT condition is signalled out during the TURN-ON PHASE so assuring correct operation for the de-