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TDA7438

THREE BANDS DIGITALLY CONTROLLED AUDIO PROCESSOR

STMicroelectronics 

TDA7438

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:

Fc

=

----------------------------1------------------------------

2 ⋅ π ⋅ Ri, R2, C1, C2

AV = -R----2----C--R---2--1---+-C----R1----2-+---C--R---1--2---+-C----R-2----i-C-----1--

Q = --R---R--2--i--,C---R--1---2--+-,---CR-----12---,-C--C---2--2--

Viceversa, once Fc, Av, and Ri internal value are fixed, the external components values will be:

C1 = 2-----⋅--A-π----V-⋅---R–-----1i--⋅---Q---

C2 = A---Q--V---2-–---⋅--1-C---Q--1---2-

R2 = 2-----⋅---π-----⋅---C----A-1---V--⋅---F–----c-1--⋅--–-(---A-Q---V--2---–----1----)---⋅----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.

14 to 17.

3.3 CREF

The suggested 10mF reference capacitor (CREF) value can be reduced to 4.7mF if the application re-

quires faster power ON.

Figure 6. THD vs. frequency

Figure 7. THD vs. RLOAD

6/19

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