TDA7402 datasheet(27/71 Pages) STMICROELECTRONICS

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TDA7402

Audioprocessor part

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volume with 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 disappears.

It is even possible to run the compression mode and the anti-clipping mode in parallel. In

this case the maximum compander gain should be set to 29dB.

4.10.2

Characteristic

To achieve the desired compression characteristic like shown below the volume has to be

decreased by 4dB.

Figure 18.

Compander characteristic

4.10.3

I²C bus timing

While 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 recommended to

change the volume during this slope. To avoid this while the compander is working and the

volume has to be changed, the compander hold-bit is implemented (Bit 7 in the subaddress

byte). The recommended timing for changing the volume during compander ON is the

following:

Set the compander hold bit

Wait the actual softstep time

Change the volume

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:

-60

-50

-40

-30

-20

-10

-20

-30

-40

-50

-60

Input Level

Output Level

-8dB

15dB

-38dB

2:1

Table 6.

Attack times vs soft-step times

Attack time

SoftStep time

6ms

0.16ms

12ms

0.32ms

24ms

0.64ms

48ms

1.28ms

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