TDA7437N Datasheet, PDF (14/23 Pages) STMicroelectronics – DIGITALLY CONTROLLED AUDIO PROCESSOR

TDA7437N
MUTE & PAUSE FEATURES
The TDA7437N provides three types of mute, controlled via I2C bus (see pag. 10, 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 capacitor Csm inserted between pin Csm and ground.
Once fixed the external capacitor, two different slopes (time constant) are selectable by programmation of bit
D1.
Bit D1 = 0 → fast slope (I=Imax)
Bit D1 = 1 → slow slope (I=Imin)
The soft mute generates a gradual signal decreasing 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 Fig.8
(mute) and Fig.9 (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 application, the soft mute ON programmation should be followed by programmation of DIRECT MUTE ON
(see later) in order to achieve a final 100dB attenuation.Beside the I²C bus programmation, 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 data sheet pag. 8).
read bit SM = 1 soft mute status ON
read bit SM = 0 soft mute status OFF
DIRECT MUTE
bit D3 = 1 Direct mute ON
bit D3 = 0 Direct nute 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.
SPEAKERS MUTE
An additional direct mute function is included in the speakers attenuators stage.
The four output LF, RF, LR, RR can be separately muted by setting the speaker attenuator byte to the value
01111111 binary.
Typical attenuation level 100dB. This mute is useful for fader and balance functions. It should not be applied for
system mute/unmute, because it can generate noise due to the offset of previous stages (bass /treble).
ZEROCROSSING MUTE
bit D2 = 1 D4 = 0 zero crossing mute ON
bit D2 = 0 D4 = 0 zero crossing mute OFF
The mute activation/deactivation is delayed until the signal waveform crosses the DC zero level (Vref level).
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