TDA7375A Datasheet, PDF (9/14 Pages) STMicroelectronics – 2 x 37W DUAL/QUAD POWER AMPLIFIER FOR CAR RADIO

High Application Flexibility
The availability of 4 independent channels makes
it possible to accomplish several kinds of applica-
tions ranging from 4 speakers stereo (F/R) to 2
speakers bridge solutions.
In case of working in single ended conditions the
polarity of the speakers driven by the inverting
amplifier must be reversed respect to those driven
by non inverting channels.
This is to avoid phase inconveniences causing
sound alterations especially during the reproduc-
tion of low frequencies.
Easy Single Ended to Bridge Transition
The change from single ended to bridge configu-
rations is made simply by means of a short circuit
across the inputs, that is no need of further exter-
nal components.
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 dis-
tortion optimization.
Silent Turn On/Off and Muting/Stand-by Func-
tion
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 = 1µA typ.; output at-
tenuation= 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 as-
signed to the SVR capacitor.
While in muting the device outputs becomes in-
sensitive to any kinds of signal that may be pre-
sent at the input terminals. In other words every
transient coming from previous stages produces
no unplesant acoustic effect to the speakers.
TDA7375A
Need of Bootstrap Capacitors.
The output swing is limited only by the VCEsat
of the output transistors, which are in the range
of 0.3Ω (Rsat) 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 signifi-
cant power reduction. The only way to recover
power consists of the addition of expensive
bootstrap capacitors.
Absolute Stability Without Any External
Compensation.
Referring to the circuit of fig. 20 the gain
VOut/VIn is greater than unity, approximately 1+
R2/R1. The DC output (VCC/2) is fixed by an
auxiliary amplifier common to all the channels.
By controlling the amount of this local feedback
it 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 stable and not prone to oscilla-
tion.
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.
Figure 20: The New Output Stage
OUTPUT STAGE
The fully complementary output stage was made
possible by the development of a new compo-
nent: the ST exclusive power ICV PNP.
A novel design based upon the connection shown
in fig. 20 has then allowed the full exploitation of
its possibilities.
The clear advantages this new approach has over
classical output stages are as follows:
Rail-to-Rail Output Voltage Swing With No
BUILT–IN SHORT CIRCUIT PROTECTION
Reliable and safe operation, in presence of all
kinds of short circuit involving the outputs is as-
sured by BUILT-IN protectors. Additionally to the
AC/DC short circuit to GND, to VS, across the
speaker, a SOFT SHORT condition is signalled
out during the TURN-ON PHASE so assuring cor-
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