7403 datasheet(8/26 Pages) STMICROELECTRONICS

8 / 26 page

Softmute

The digitally controlled softmute stage allows

muting/demuting the signal with a I

2C bus pro-

grammable slope. The mute process can either

be activated by the softmute pin or by the I

bus. The slope is realized in a special S shaped

curve to mute slow in the critical regions (see fig-

ure 5).

For timing purposes the Bit 3 of the I

2C bus out-

put register is set to 1 from the start of muting un-

til the end of demuting.

Softstep Volume

When volume level is changed often an audible

click appears at the output. The root cause of

those clicks could be either a DC offset before

the volume stage or the sudden change of the

envelope of the audio signal. With the Softstep

feature both kinds of clicks could be reduced to a

minimum and are no more audible (see figure 6).

Bass

There are three parameters programmable in the

bass stage (see figs 7, 8, 9, 10):

- Attenuation

- Center Frequency (60, 70, 80 and 100Hz)

- Quality Factors (1, 1.25, 1.5 and 2)

DC Mode

In this mode the DC gain is increased by 4.4dB.

In addition the programmed center frequency and

quality factor is decreased by 25% which can be

used to reach alternative center frequencies or

quality factors.

Treble

There are two parameters programmable in the

treble stage (see figs 11, 12):

- Attenuation

- Center Frequency (10, 12.5, 15 and 17.5kHz).

Speaker Attenuator

Due to practical aspects the steps in the speaker

attenuators are not linear over the full range. At

attenuations more than 24dB the steps increase

from 1.5dB to 10dB (please see data byte specifi-

cation).

100

1,000

-20

-15

-10

-5

(dB)

D98AU844

Figure 4. Loudness @ Attn. = 15dB, fc = 400Hz

EXT.

MUTE

+SIGNAL

REF

-SIGNAL

C BUS

OUT

Time

D97AU634

Figure 5. Softmute Timing

2dB

1dB

-1dB

-2dB

Time

D97AU635

VOUT

10ms

Figure 6. Soft Step Timing

Note: Please notice that a started Mute action is always terminated

and could not be interrupted by a change of the mute signal.

Note: For steps more than 1dB the softstep mode should be

deactivated because it could generate a 1dB error during the

blend-time

TDA7403

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