TDA7449_04 Datasheet, PDF (6/19 Pages) STMicroelectronics – TONE CONTROL DIGITALLY CONTROLLED AUDIO PROCESSOR

TDA7449
3 APLICATION 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 TDA7449 audioprocessor
provides 2 bands tones control.
3.1 Bass, Stages
The Bass cell has an internal resistor Ri = 25KΩ typical. Several filter types can be implemented, connect-
ing external components to the Bass IN and OUT pins. The fig.6 refers to basic T Type Bandpass Filter
starting from the filter component values (R1 internal Fc, the gain Av at max. boost and the filter Q factor
are computed as follows:
Figure 6.
Ri internal
IN
OUT
C₁
C₂
R₂
D95AU313
F_C
=
--------------------------------¹---------------------------------
2 ⋅ π ⋅ R1 ⋅ R2 ⋅ C1 ⋅ C2
A_V = ^R-----²----^C--_R---²--₂---+-_C----^R1----²-+---^C--_R---¹--₂---+-_C----^R-₂----ⁱ-^C-----¹--
Q = -----^R-_R----¹-₂---^â‹_C---^R--₁---²--+---^â‹--_R-^C----₂-¹---_C--^â‹--₂-^C----²--
Viceversa, once Fc, Av, and Ri internal value are fixed, the external components values will be:
C1 = ₂-----_â‹---_π-----_â‹^A---_F--^V--_c--–---_â‹--¹-_R----_i----_â‹--_Q----
C2 = _A-----_V^Q----–-²----₁-^â‹---^C-–---¹-_Q-----₂-
R2 = -₂----_â‹---_π-----_â‹---_C-----^A1----^V-_â‹---_F^–----_c-¹---_â‹--–-₍---_AQ----_V-²----–----₁----₎---_â‹---_Q----
3.2 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.
10 to 13.
3.3 CREF
The suggested 10µF reference capacitor (CREF) value can be reduced to 4.7µF if the application requires
faster power ON.
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