TDA7385 Datasheet, PDF (8/12 Pages) STMicroelectronics – 4 x 30W QUAD BRIDGE CAR RADIO AMPLIFIER

TDA7385
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
(0.1µF) is adopted, the low frequency cut-off will
amount to 16 Hz.
tion with microprocessor-driven audioprocessors.
The maximum load that pin 25 can sustain is
1KΩ.
Due to its operating principles, the clipping detec-
tor has to be viewed mainly as a power-depend-
Figure 12: Diagnostics circuit.
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-
ries resistance (R2) is 70KΩ, which is sufficiently
high to permit a muting capacitor reasonably
small (about 1µF).
If R₂ is higher than recommended, the involved
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.
25
R
Vpin 25
VREF
TDA7385
D95AU303
Figure 13: Clipping Detection Waveforms.
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-
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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^oC before the thermal shut-down threshold is