TDA7402_07 Datasheet, PDF (21/71 Pages) STMicroelectronics – Car radio signal processor

TDA7402
Audioprocessor part
4.4
SoftMute
The digitally controlled SoftMute stage allows muting/demuting the signal with a I²C bus
programmable slope. The mute process can either be activated by the SoftMute pin or by
the I²C-bus. This slope is realized in a special S-shaped curve to mute slow in the critical
regions (see Figure 7).
For timing purposes the Bit0 of the I²C bus output register is set to 1 from the start of muting
until the end of de-muting.
Figure 7. Softmute timing
Note:
1
EXT.
MUTE
+SIGNAL
REF
-SIGNAL
1
I²C BUS
OUT
D97AU634
Time
Please notice that a started mute action is always terminated and could not be interrupted
by a change of the mute -signal.
4.5
SoftStep volume
When the volume level is changed audible clicks could appear at the output. The root cause
of those clicks could either be a DC offset before the volume stage or the sudden change of
the envelope of the audiosignal. With the SoftStep feature both kinds of clicks could be
reduced to a minimum and are no more audible. The blend time from one step to the next is
programmable in four steps.
Figure 8. SoftStep timing
V_OUT
1dB
0.5dB
-0.5dB
-1dB
SS Time
Time
D00AU1170
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