TDA7340G Datasheet, PDF (22/27 Pages) STMicroelectronics – AUDIO SIGNAL PROCESSOR

TDA7340G
No possibility to change the loud boost rate at a
certain volume level.
The TDA7340G implements a fully programmable
loudness control in 15 steps of 1.25dB.
It allows a customized loudness response for
each application.
The external network connected to the loudness
pins LOUD_L and LOUD_R fixes the type of loud-
ness response
1) Simple Capacitor
The loudness effect is only a boost of low fre-
quencies. (see Fig.20)
2)Second order Loudness (boost of low and
high frequencies).
3)Second order decreased type Loudness
(lower boost of low and high frequencies).
4)Second order modified type Loudness (higher
boost of low and high frequencies).
BASS FILTER
Several bass filter types can be implemented.
Normally it is used the basic T-type Bandpass Filter.
Starting from the filter component values (R1 in-
ternal and R2, C1, C2 external), the centre fre-
quency Fc, the gain Av at max bass boost and
the filter Q factor are computed as follows:
F_c =
1
2 ⋅ Π ⋅ √(R1⋅R2⋅C1⋅C2)
A_v
=
R2⋅
C2 +
R2 ⋅
R2
C1
⋅ C1 +
+ R2 ⋅
R1
C2
⋅
C1
Q
=
√(R1⋅ R2⋅C1⋅C2)
R2 ⋅ C1 + R2 ⋅ C2
Viceversa fixed Fc, Av, and R1 = 50KΩ (internal
typ.+/-30%), the external component values are:
C1 = ^{Av − 1}
2 ⋅ Π ⋅ R1 ⋅ Q
C2
=
Q ⋅ Q ⋅ C1
Av − 1 − Q ⋅ Q
R2
=
2
⋅
Π
⋅
A_v − 1 − Q ⋅ Q
C1 ⋅ F_c ⋅ (A_v −
1)
⋅
Q
TREBLE STAGE
The Treble stage is a simple high pass filter which
time constant is fixed by internal resistor (50Kohm
typ) and an external capacitor connected between
pins TREB_R/TREB_L and Ground.
IN-OUT PINS
The multiplexer output is available at OUT_R and
OUT_L pins for optional connection of external
graphic equalizer (TDA7316/TDA7317), surround
chip (TDA7346) etc.
The signal is fed in again at pins IN_L and IN-R.
In case of application without external devices the
pins OUT_L/OUT_R and IN_L/IN_R cannot be
short circuited, but must be decoupled via capaci-
tor, necessary to avoid signal DC jumps, generat-
ing ”Clicking” output noise.
The input impedance of the next volume stage is
35Kohm typical (minimum 24Kohm). A capacitor
no lower than 1uF should be used.
INPUT SELECTOR
The multiplexer selector can choose one of the
following inputs:
- a differential CD stereo input.
- an FM stereo input coming from the on chip-
stereo decoder.
- a Cassette stereo input.
- a Telephone Differential mono input.
- an AM stereo input or alternatively (sw pro-
grammable) an AM mono + BEEP mono.
The signal fed to the input pins must be decou-
pled via series capacitors. The minimum allowed
value depends on the correspondent input imped-
ance.
For the CD diff input (Zi=10Kohm worst case ) a
Cin=4.7uF is recommended.
For the other inputs (70Kohm worst case, except
PHONE 14Kohm worst case but speech audio
band) a Cin=1uF is recommended.
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