9/15
TDA7375V
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.
The output swing is limited only by the V
CEsat
of the output transistors, which is in the range of 0.3(R
sat
)
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.
Referring to the circuit of fig. 23 the gain V
Out
/V
In
is greater than unity, approximately 1+R2/R1. The DC
output (V
CC
/2) is fixed by an auxiliary amplifier common to all the channels.
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
BUILT-IN protectors. Additionally to the AC/DC short circuit to GND, to V
S
, across the speaker, a SOFT
SHORT condition is signalled out during the TURN-ON PHASE so assuring correct operation for the de-
