INPUT STAGE

The TDA7385’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 TDA7385 is equipped with a diagnostics cir-

cuitry able to detect the following events:

CLIPPING in the output stage

OVERHEATING

(THERMAL

SHUT-DOWN

proximity)

OUTPUT MISCONNECTIONS (OUT-GND &

OUT-Vs shorts)

Diagnostics information is available across an

open collector output located at pin 25 (fig. 12)

through a current sinking whenever at least one

of the above events is recognized.

Among them, the CLIPPING DETECTOR acts in

a way to output a signal as soon as one or more

power transistors start being saturated.

As a result, the clipping-related signal at pin 25

takes the form of pulses, which are perfectly syn-

cronized with each single clipping event in the

music program and reflect the same duration time

(fig. 13).

Applications making use of this facility

usually operate a filtering/integration of the pulses

train through passive R-C networks and realize a

volume (or tone bass) stepping down in associa-

tion with microprocessor-driven audioprocessors.

The maximum load that pin 25 can sustain is

1K

Ω.

Due to its operating principles, the clipping detec-

tor has to be viewed mainly as a power-depend-

ent feature rather than frequency-dependent.This

means that clipping state will be immediately sig-

naled out whenever a fixed power level is

reached, regardless of the audio frequency.

In other words, this feature offers the means to

counteract the extremely sound-damaging effects

of clipping, caused by a sudden increase of odd

order harmonics and appearance of serious inter-

modulation phenomena.

Another possible kind of distortion control could

be the setting of a maximum allowable THD limit

(e.g. 0.5 %) over the entire audio frequency

range. Besides offering no practical advantages,

this procedure cannot be much accurate, as the

non-clipping distortion is likely to vary over fre-

quency.

In case of OVERHEATING, pin 25 will signal out

the junction temperature proximity to the thermal

shut-down threshold. This will typically start about

2

VREF

R

Vpin 25

25

D95AU303

TDA7385

Figure 12: Diagnostics circuit.

Figure 13: Clipping Detection Waveforms.

TDA7385

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