TDA7405 datasheet(21/56 Pages) STMICROELECTRONICS

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TDA7405

2.10.3Characteristic

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

Figure 18. Compander Characteristic

2.10.4I²C -BUS-Timing

When the Compander is active 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 de-

scription of this stage it is not recommended to change the volume during this slope. To avoid this behaviour-

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:

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:

2.10.5AC-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 I²C-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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