TDA7541B datasheet(34/77 Pages) STMICROELECTRONICS

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Functional description

TDA7541B

34/77

Doc ID 16048 Rev 1

10k between FSU pin and FSTC pin. The second stage is a programmable gain stage to

adapt the VFSTC signal internally. The gain (LG) is widely programmable in 16 steps from

0 dB to 8.25 dB (step=0.55dB). These 4 bits are located together with the Roll-Off

compensation bits in byte 14 to simplify a possible adaptation during the production of the car radio.

Stereo blend control

The stereo blend 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 VREF1. The lower limit can be programmed between 29 and

58 % of VREF1 in 4 % steps. In order to adjust the external voltage VFSTC to the internal

control range two values must be defined: the Level gain LG and VSBL. Full channel

separation is reached when the internal level voltage (VST) becomes bigger than VREF1.

Therefore the following equation can be used to estimate the gain:

The MONO-voltage VMO (0dB channel separation) can be chosen selecting SBC.

Figure 4.

Programming of stereo blend

High cut control

The high cut control set-up is similar to the stereo blend 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.

4.3.2

Noise blanker

In the automotive environment spikes produced for example by the ignition or the wiper-

motor disturb the MPX-signal. The aim of the noise blanker part is to cancel the audible

influence of the spikes. Therefore the output of the stereo decoder is held at the actual

voltage for a time between 22 ms and 38 ms (programmable).

In a first stage the spikes must be detected but to avoid a wrong triggering on high

frequency (white) noise a complex trigger control is implemented. Behind the trigger stage a

pulse former generates the "blanking"-pulse. An own biasing circuit supplies the noise

blanker in order to avoid any cross talk to the signal path.

REF1

FSTC @ fullstereo

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TDA7541B Datasheet(PDF) 34 Page - STMicroelectronics