TDA7284 Datasheet, PDF (10/14 Pages) STMicroelectronics – RECORD/PLAYBACK CIRCUIT WITH ALC

TDA7284
peak-to-peak detector of fig. 16 is now inside the
broken line 1 while the system which allows a di-
namic resistance varying with the DC voltage
level (i.e. inversely proportional to the op-amp
output signal),is inside the broken line 2.
It should be noted that the generator resistance
Ri has no influence on the controlled voltage
value Vc, although its value should be between 1
and 47 Kohm.
The lower limit is determined by the minimum dy-
namic resistance of 10 ohm and therefore to
have a control range of 40 dB for the input signal,
Ri must be greather than 1.5 Kohm.
The upper limit results from the necessity to limit
the attenuation of the signal by the input imped-
ance of the op-amp.
Switches
Two DC-controlled switches are also included in
the chip (fig. 20 )
Fig. 19 shows the typical application circuit of the
TDA7284 utilizing the equalization switch for nor-
mal or chrome tape playback equalization.The
advantage is the components can be placed near
Figure 20
to the IC, while the tape selector switch can be at
a remote location, hence reduce the chances of
noise and oscillation due to components layout.
Another advantage is that only one pole is
needed for the tape selector switch as compared
to the two poles needed by conventional circuits
(one separate pole for each channel).
Fig. 22 shows the use of the switches to obtain
the mute function.
Figure 21: Application Circuit with DC Switching of Normal/Chrome Tape Equalization
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