TDA7540N datasheet(31/76 Pages) STMICROELECTRONICS

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TDA7540N

Functional description

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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

VREF1 in 4% steps (see Figure 6).

To adjust the external LEVEL-voltage to the internal range two values must be defined: the

LEVEL gain LG and VSBL. To adjust the voltage where the full channel separation is

reached (VST) the LEVEL gain LG has to be defined. The following equation can be used to

estimate the gain:

LG = VREF1/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 Figure 7).

Figure 7.

Highcut characteristics

Lowpass

time constant

VHCL

VHCHFieldstrength

3 • Deemp

τ Deemp

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