TDA7461N_03 Datasheet, PDF (8/32 Pages) STMicroelectronics – CAR RADIO SIGNAL PROCESSOR

TDA7461N
How to find the right input configuration
The best way to come to the desired configura-
tion may be to go through the application tree
from the top to the bottom while making the spe-
cific decisions.
This way will lead to one of the six possible appli-
cations. Then take the number of the application
and go into the pinning table. Here you will find
the special pinout as well as the special program-
ming codes for selecting sources.
For example in Appl. 6 the TDA7461N has to be
configured while startup with the databyte
0/xxxx0xxx.
To select the FM, AM or phone source the last
five significant bits of subaddress 0 have to be
changed, for any other source the last three bits
are sufficient (see data byte specification).
Input stages
Most of the input circuits are the same as in pre-
ceeding ST audioprocessors with exception of
the CD inputs (see figure 2).
In the meantime there are some CD players in
the market having a significant high source im-
pedance which affects strongly the common-
mode rejection of the normal differential input
stage. The additional buffer of the CD input
avoids this drawback and offers the full common-
mode rejection even with those CD players.
The TDA7461N can be configured with an addi-
tional input; if the AC coupling before the speaker
stage is not used (bit 7 in subaddress 5 set to "1")
ACINL and ACINR pins can be used as an addi-
tional stereo input.
AutoZero
In order to reduce the number of pins there is no
AC coupling between the In-Gain and the follow-
ing stage, so that any offset generated by or be-
fore the In-Gain stage would be transferred or
even amplified to the output.
To avoid that effect a special offset cancellation
stage called AutoZero is implemented.
To avoid audible clicks the audioprocessor is
muted before the loudness stage during this time.
In some cases, for example if the µP is executing
a refresh cycle of the I²C bus programming, it is
not useful to start a new AutoZero action because
no new source is selected and an undesired mute
would appear at the outputs. For such applica-
tions the TDA7461N could be switched in the
"Auto Zero Remain" mode (Bit 6 of the subad-
dress byte). If this bit is set to high, the DAT-
ABYTE 0 could be loaded without invoking the
AutoZero and the old adjustment value remains.
MUX OUTPUT
The MUX_L and MUX_R outputs can provide se-
lectively the output of the input multiplexer
(Speaker RF register, Byte 8, bit 6=1) or the out-
put of the stereodecoder (Speaker RF register
Byte 8 bit 6=0).
If bit D3 byte 10 (Stdec Register) is set to 1, then
the stdec signal is automatically muted, when an-
other source is selected at the input multiplexer.
If bit D3 byte 10 (Stdec Register) is set to 0, then
the stdec signal will be always available at the
Mux out pins, no matter which is the selected
source.
The selection of the stereodecoder input, via a
special procedure, is recommended.
1)Soft Mute or Mute the signal path
2)Temporary deselect the stereodec
3) Wait 100-200ms to allow the stdec internal
filters to settle
4) Select sterodec input (with automatic autozero)
This procedure guarantees an optimum offset-
cancellation, avoiding big DC offsets due to the
autozero circuitry, which otherwise could try to
compensate the signal sourced at the MPX input
instead of the stereodecoder intrinsic offset.
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