APPLICATION HINTS (ref. to the circuit of fig. 1)

BIASING AND SVR

As shown by fig. 3, all the TDA7381’s main sec-

tions, such as INPUTS, OUTPUTS AND AC-GND

(pin 16) are internally biased at half Supply Volt-

age level (Vs/2), which is derived from the Supply

Voltage Rejection (SVR) block. In this way no cur-

rent flows through the internal feedback network.

The AC-GND is common to all the 4 amplifiers

and represents the connection point of all the in-

verting inputs.

Both individual inputs and AC-GND are con-

nected to Vs/2 (SVR) by means of 100K

Ω resis-

tors.

To ensure proper operation and high supply volt-

age rejection, it is of fundamental importance to

provide a good impedance matching between IN-

PUTS and AC-GROUND terminations. This im-

TO CARRY THE SAME NOMINAL VALUE AND

THEIR TOLERANCE SHOULD NEVER EXCEED

±10 %.

Besides its contribution to the ripple rejection, the

SVR capacitor governs the turn ON/OFF time se-

quence and, consequently, plays an essential role

in the pop optimization during ON/OFF transients.

To conveniently serve both needs, ITS MINIMUM

RECOMMENDED VALUE IS 10

µF.

INPUT STAGE

The TDA7381’S inputs are ground-compatible

and can stand very high input signals (

± 8Vpk)

without any performances degradation.

If the standard value for the input capacitors

(0.1

µF) is adopted, the low frequency cut-off will

amount to 16 Hz.

STAND-BY AND MUTING

STAND-BY and MUTING facilities are both

CMOS-COMPATIBLE. If unused, a straight con-

nection to Vs of their respective pins would be ad-

missible. Conventional low-power transistors can

be employed to drive muting and stand-by pins in

absence of true CMOS ports or microprocessors.

R-C cells have always to be used in order to

smooth down the transitions for preventing any

audible transient noises.

Since a DC current of about 10 uA normally flows

out of pin 22, the maximum allowable muting-se-

Ω, which is sufficiently

high to permit a muting capacitor reasonably

small (about 1

µF).

risk will be that the voltage at pin 22 may rise to

above the 1.5 V threshold voltage and the device

will consequently fail to turn OFF when the mute

line is brought down.

About the stand-by, the time constant to be as-

signed in order to obtain a virtually pop-free tran-

sition has to be slower than 2.5V/ms.

DIAGNOSTICS FACILITY

The TDA7381 is equipped with a diagnostics cir-

cuitry able to detect the following events:

CLIPPING in the output stage

OVERHEATING

(THERMAL

SHUT-DOWN

proximity)

+

-

0.1

µF

C1

÷ C4

+

-

8K

Ω

8K

Ω

400

Ω

400

Ω

100K

Ω

100K

Ω

70K

Ω

IN

D95AU302

TOWARDS

OTHER CHANNELS

10K

Ω

10K

Ω

47

µF

C6

0.1

µF

C5

SVR

AC_GND

Figure 3: Input/OutputBiasing.

TDA7381

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