TDA7440D
3
APPLICATION SUGGESTIONS
The first and the last stages are volume control blocks. The control range is 0 to -47dB (mute) for the first
one, 0 to -79dB (mute) for the last one. Both of them have 1dB step resolution. The very high resolution
allows the implementation of systems free from any noisy acoustical effect.
The TDA7440D audioprocessor provides 3 bands tones control.
3.1 Bass Stage
Several filter types can be implemented, connecting external components to the Bass IN and OUT pins.
The fig.5 refers to basic T Type Bandpass Filter starting from the filter component values (R1 internal and
R2,C1,C2 external) the centre frequency Fc, the gain Av at max. boost and the filter Q factor are computed
as follows:
1
F
C
= -----------------------------------------------------------------
2
⋅ π ⋅
R1
⋅
R2
⋅
C1
⋅
C2
R2 C2
+
R2 C1
+
R
i
C1
-
A
V
= ---------------------------------------------------------------
R2 C1
+
R2 C2
R1
⋅
R2
⋅
C1
⋅
C2
Q
= -------------------------------------------------
-
R2 C1
+
R2 C2
Viceversa, once Fc, Av, and Ri internal value are fixed, the external components values will be:
A
V
–
1
-
C1
= -----------------------------------------
2
⋅ π ⋅
F
C
⋅
R
i
⋅
Q
Figure 5.
Ri internal
IN
C
1
R
2
D95AU313
Q
⋅
C1
-
C2
= -----------------------------
2
A
V
–
1
–
Q
2
A
V
–
1
–
Q
R2
= ----------------------------------------------------------------------
-
2
⋅ π ⋅
C1
⋅
F
C
⋅ (
A
V
–
1
) ⋅
Q
2
OUT
C
2
Treble Stage
The treble stage is a high pass filter whose time constant is fixed by an internal resistor (25KΩ typical) and
an external capacitor connected between treble pins and ground.
Typical responses are reported in Figg. 14 to 17.
CREF
The suggested 10mF reference capacitor (CREF) value can be reduced to 4.7mF if the application re-
quires faster power ON.
5/17
STMICROELECTRONICS [ STMICROELECTRONICS ]
