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

reached.

As various kind of diagnostics information is avail-

able at pin 25 (CLIPPING, SHORTS AND OVER-

HEATING), it may be necessary to operate some

distinctions on order to treat each event sepa-

rately. This could be achieved by taking into ac-

count the intrinsically different timing of the diag-

nostics output under each circumstance.

In fact, clipping will produce pulses normally

much shorter than those present under faulty con-

ditions. An example of circuit able to distinguish

between the two occurrences is shown by fig. 7.

STABILITY AND LAYOUT CONSIDERATIONS

If properly layouted and hooked to standard car-

radio speakers, the TDA7381 will be intrinsically

stable with no need of external compensations

such as output R-C cells. Due to the high number

of channels involved, this translates into a very

remarkable components saving if compared to

similar devices on the market.

To simplify pc-board layout designs, each ampli-

fier stage has its own power ground externally ac-

cessible (pins 2,8,18,24) and one supply voltage

pin for each couple of them.

Even more important, this makes it possible to

achieve the highest possible degree of separation

among the channels, with remarkable benefits in

terms of cross-talk and distortion features.

About the layout grounding, it is particularly im-

the signal GND, as close as possible to the audio

inputs ground: this will guarantee high rejection of

any common mode spurious signals.

to the signal GND.

to be connected to the power-ground and located

as close as possible to the Vs pins.

Pin 1, which is mechanically attached to the de-

vice’s tab, needs to be tied to the cleanest power

ground point in the pc-board, which is generally

near the supply filtering capacitors.

CLIP DET. (TO GAIN

COMPRESSOR/

TONE CONTROL)

T1

25

D95AU305

TDA7385

+

-

VREF

VREF1

T2

FAULT, THERMAL SHUTDOWN

(TO POWER SUPPLY

SECTION,

µP VOLTAGE

REGULATOR, FLASHING SYSTEM)

+

-

VREF2

T1 << T2

VREF

≥ VREF1 >> VREF2

Figure 7.

TDA7381

TDA7381

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