TDA7402 datasheet(21/59 Pages) STMICROELECTRONICS

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TDA7402

the same value in order to get the desired output-level. In clipping situation the open-collector-current generates

a voltage-drop at the rectifier-input, which forces the compander to decrease the gain until the clipping disap-

pears.

It is even possible to run the compression-mode and the Anti-Clipping mode in parallel. In this case the maxi-

mum Compander-Gain should be set to 29dB.

1.11.1Characteristic

To achieve the desired compression characteristic like shown below the volume has to be decreased by 4dB.

Figure 16. Compander Characteristic

1.11.2I C -BUS-Timing

During the Compander is working a volume-

word coming from this stage is added to the

I2C-Bus volume-word and the volume is

changed with a soft slope between adjacent

steps (SoftStep-stage). As mentioned in the

description of this stage it is not recommend-

ed to change the volume during this slope. To

avoid this while the Compander is working

and the volume has to be changed, the com-

pander-hold-bit is implemented (Bit 7 in the

subaddress-byte). The recommended timing

for changing the volume during compander-

ON is the following:

1. Set the compander-hold-bit

2. Wait the actual SoftStep-time

3. Change the volume

4. Reset the compander-hold-bit

The SoftStep-times are in compander-ON condition automatically adapted to the attack-time of the Compander.

In the following table the related SoftStep-times are shown:

1.12 AC-Coupling

In some applications additional signal manipulations are desired, for example surround-sound or more-band-

equalizing. For this purpose an AC-Coupling is placed before the speaker-attenuators, which can be activated

or internally shorted by I C-Bus. In short condition the input-signal of the speaker-attenuator is available at the

AC-Outputs. The input-impedance of this AC-Inputs is 50k

Ω.

Attack-Time

SoftStep-Time

6ms

0.16ms

12ms

0.32ms

24ms

0.64ms

48ms

1.28ms

-60

-50

-40

-30

-20

-10

-20

-30

-40

-50

-60

Input Level

Output Level

-8dB

15dB

-38dB

2:1

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