E-TDA7437N View Datasheet(PDF) - STMicroelectronics
Part Name
Description
MFG CO.
'E-TDA7437N' PDF : 34 Pages View PDF
Mute and pause features
5
Mute and pause features
TDA7437N
The TDA7437N provides three types of mute, controlled via I2C bus (see Table 9 Mute byte
register).
5.1
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 capacitor Csm inserted between pin Csm and
ground.
Once the external capacitor is fixed, two different slopes (time constant) are selectable by
programming of bit D1.
Bit D1 = 0 → fast slope (I=Imax)
Bit D1 = 1 → slow slope (I=Imin)
The soft mute generates a gradually decreasing signal, avoiding big click noise of an
immediate high attenuation, without necessity to program a sequence of decreasing volume
levels. A response example is reported in Figure 11 (mute), and Figure 12 (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. 8mswhen selected Fast slope mode (bit D1=0)
d = 25 ms when selected Slow slope mode (bit D1=1
In the application, the soft mute ON programming should be followed by programming of
direct mute on (see 5.2), in order to achieve a final 100dB attenuation. In addition to the I2C
bus programming, the Soft Mute ON can be generated in a fast way by forcing a LOW level
at pin SMEXT (TTL Level compatible). This approach is recommended for fast RDS AF
switching.
The Soft Mute status can be detected via I2C bus, reading the Transmitted Byte, bit SM
(see Table 6).
read bit SM = 1 soft mute status ON
read bit SM = 0 soft mute status OFF
5.2
Direct mute
bit D3 = 1 Direct mute ON
bit D3 = 0 Direct mute OFF
The direct mute bit forces an internal immediate signal connection to ground.
It is located just before the Volume/Loudness stage, and gives a typical 100dB attenuation.
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