TDA7402 Datasheet, PDF (21/59 Pages) STMicroelectronics – CARRADIO SIGNAL PROCESSOR

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
0
-10
Output Level
-20
dB
-30
-40
-50
-60
0
-8dB
2:1
-10
-20
-30
Input Level
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
-38dB
steps (SoftStep-stage). As mentioned in the
description of this stage it is not recommend-
ed to change the volume during this slope. To
15dB
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-
-40
-50
-60 _{ON is the following:}
dB
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
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 50kΩ.
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