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 = 1

µA 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.

STAND-BY DRIVING (pin 7)

Some precautions have to be taken in the defini-

tion of stand-by driving networks: pin 7 cannot be

directly driven by a voltage source whose current

capability is higher than 5mA. In practical cases

a series resistance has always to be inserted,

having it the double purpose of limiting the cur-

rent at pin 7 and to smooth down the stand-by

ON/OFF transitions - in combination with a ca-

pacitor - 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.

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

Need of Bootstrap Capacitors.

The output swing is limited only by the VCEsat

of the output transistors, which is in the range

of 0.3

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

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 in-

trinsically stable and 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.

BUILT–IN SHORT CIRCUIT PROTECTION

Figure 20: The New Output Stage

TDA7375

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