TDA7340G datasheet(22/27 Pages) STMICROELECTRONICS

22 / 27 page

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:

⋅ Π ⋅√

(R1 ⋅ R2 ⋅ C1 ⋅ C2)

Av =

⋅ C2 + R2 ⋅ C1 + R1 ⋅ C1

⋅ C1 + R2 ⋅ C2

√

(R1 ⋅ R2 ⋅ C1 ⋅ C2)

⋅ C1 + R2 ⋅ C2

Viceversa fixed Fc, Av, and R1 = 50K

Ω (internal

typ.+/-30%), the external component values are:

− 1

⋅ Π ⋅ R1 ⋅ Q

⋅ Q ⋅ C1

− 1 − Q ⋅ Q

⋅ Π ⋅ C1 ⋅ Fc ⋅ (Av − 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.

TDA7340G

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