TDA7540B Datasheet, PDF (28/75 Pages) STMicroelectronics – AM/FM Car Radio Tuner IC with Stereo Decoder and Intelligent Selectivity System (ISS)

Functional description
TDA7540B
Stereoblend control
The stereoblend control block converts the internal LEVEL-voltage into a demodulator
compatible analog signal, which is used to control the channel separation between 0dB and
the maximum separation. Internally this control range has a fixed upper limit, which is the
internal reference voltage . V_REF1 The lower limit can be programmed between 29 and 58% of
V_REF1 in 4% steps (see fig.6).
To adjust the external LEVEL-voltage to the internal range two values must be defined: the
LEVEL gain L_G and VSBL. To adjust the voltage where the full channel separation is reached
(VST) the LEVEL gain L_G has to be defined. The following equation can be used to estimate
the gain:
L_G = V_REF1/FSU@full stereo
The MONO-voltage VMO (0dB channel separation) can be chosen selecting VSBL.
Figure 6. Relation between internal and external level-voltagees and setup of stereoblend
The stereo blend function can be switched ON/OFF using bit Addr25<d2>. Please note that
in AM it must be switched in forced mono!
Highcut control
The highcut control set-up is similar to the stereoblend control set-up: the starting point
VHCH can be set with 2 bits to be 42, 50, 58 or 66% of _VREF1 whereas the range can be set
to be 11, 18.3, 25.7 or 33% of VHCH (see fig. 7).
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