TDA7340G Datasheet, PDF (19/27 Pages) STMicroelectronics – AUDIO SIGNAL PROCESSOR

Figure 6: Behaviour of the Field Strength Controlled Threshold Adjustment
VPEAK
≈3V
MONO
STEREO
TRIG. THRESHOLD
NOISE
2.2V(00)
1.8V(01)
1.2V(10)
ATC_SB OFF (11)
TDA7340G
0.9V
noisy signal
good signal
E’
D95AU333A
Figure 7: Behaviour of the Deviation Dependent Threshold Adiust (Over Deviation Detector)
VPEAK
(V)
3.2
2.3
1.3
0.9
OVM=00
OVM=01
OVM=10
DETECTOR OFF (11)
D95AU332A 20 32.5
45
75
DEVIATION(KHz)
MUTE & PAUSE FEATURES
The TDA7340G provides three types of mute,
controlled via I2C bus (see pag.12, MUTE BYTE
register).
SOFT MUTE
Bit D0=1 → Soft Mute ON
Bit D0=0 →Soft Mute OFF
It allows an automatic soft muting and unmuting
of the signal.
The time constant is fixed by an external capaci-
tor Csm inserted between pin Csm and ground.
Once fixed the external capacitor, two different
slopes (time constant) are selectable by program-
mation of bit D1.
Bit D1=1 → fast slope (I=Imax)
Bit D1=0 → slow slope (I=Imin)
The soft mute generates a gradual signal de-
creasing avoiding big click noise of an immediate
high attenuation, without necessity to program a
sequence of decreasing volume levels. A re-
sponse example is reported in Fig.12 (mute) and
Fig.13 (unmute). The final attenuation obtained
with soft mute ON is 60dB typical.
The used reference parameter is the delay time
taken to reach 20dB attenuation (no matter what
the signal level is).
Using a capacitor Csm=22nF this delay is:
d = 1. 8ms when selected Fast slope mode (bit D1=1)
d = 25 ms when selected Slow slope mode (bit D1=0)
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