TDA7375A_05 Datasheet, PDF (9/15 Pages) STMicroelectronics – 2 X 37W DUAL/QUAD POWER AMPLIFIER FOR CAR RADIO

TDA7375A
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:
5.5.1 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 0.3Ω (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.
5.5.2 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*β) 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.
5.6 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-
vice itself and for the loudspeaker.
This particular kind of protection acts in a way to avoid that the device is turned on (by ST-BY) when a
resistive path (less than 16 ohms) is present between the output and GND. As the involved circuitry is nor-
mally disabled when a current higher than 5mA is flowing into the ST-BY pin, it is important, in order not
to disable it, to have the external current source driving the ST-BY pin limited to 5mA.
This extrafunction becomes particularly attractive when, in the single ended configuration, one capacitor
is shared between two outputs (see fig. 24). Supposing that the output capacitor C_out for anyreason is
shorted, the loudspeaker will not be damaged being this soft short circuit condition revealed.
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