TDA7405_04 Datasheet, PDF (21/57 Pages) STMicroelectronics – EQUALIZER CARRADIO SIGNAL PROCESSOR

TDA7405
5.10.3 Characteristic
To achieve the desired compression characteristic like shown below the volume has to be decreased by 4dB.
Figure 22. Compander Characteristic
0
-10
Output Level
-20
dB
-30
-8dB
2:1
-38dB
15dB
-40
-50
-60
0
-10
-20
-30
-40
-50
-60
Input Level
dB
5.10.4I²C -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:
Attack-Time
6ms
12ms
24ms
48ms
SoftStep-Time
0.16ms
0.32ms
0.64ms
1.28ms
5.10.5 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 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 50kΩ.
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