TDA7449 datasheet(6/17 Pages) STMICROELECTRONICS

6 / 17 page

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 TDA7449 audioprocessor provides 2 bands

tones control.

Bass, Stages

The Bass cell has an internal resistor Ri = 25K

Ω

typical.

Several filter types can be implemented, connect-

ing external components to the Bass IN and OUT

pins.

The fig.1 refers to 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. boost and the fil-

ter Q factor are computed as follows:

⋅

π ⋅√

Ri, R2, C1, C2

= R2 C2 + R2 C1+ Ri C1

R2 C1

+ R2 C2

= √

Ri R2

+ C1 C2

R2 C1

+ R2 C2

Viceversa, once Fc, Av, and Ri internal value are

fixed, the external components values will be:

− 1

⋅

π ⋅ Ri ⋅ Q

2 ⋅ C1

(AV − 1) Q2

− 1 − Q2

⋅ π ⋅ C1

⋅ FC ⋅ (AV − 1) ⋅Q

Treble Stage

The treble stage is a high pass filter whose time

constant is fixed by an internal resistor (25K

Ω

typical) and an external capacitor connected be-

tween treble pins and ground

Typical responses are reported in Figg. 10 to 13.

CREF

The suggested 10

µF reference capacitor (CREF)

value can be reduced to 4.7

µF if the application

requires faster power ON.

Ri internal

OUT

D95AU313

Figure 1.

Figure 2: THD vs. frequency

Figure 3: THD vs. RLOAD

TDA7449

6/17

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