TDA7540N STMicroelectronics, TDA7540N Datasheet - Page 30

• Manufacturer Part Number: TDA7540N
• Description: IC TUNER AM/FM CAR RADIO 80-LQFP
• Manufacturer: STMicroelectronics

Specifications of TDA7540N

• Frequency: 10.7MHz
• Modulation Or Protocol: AM, FM
• Applications: Automotive Audio
• Current - Receiving: 12mA
• Data Interface: PCB, Surface Mount
• Antenna Connector: PCB, Surface Mount
• Voltage - Supply: 7.7 V ~ 9 V
• Operating Temperature: -40°C ~ 85°C
• Package / Case: 80-LQFP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Features: -
• Sensitivity: -
• Memory Size: -
• Data Rate - Maximum: -
• Lead Free Status / Rohs Status: Compliant

Functional description
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Demodulator
In the demodulator block the left and the right channel are separated from the MPX-signal.
In this stage also the 19-kHz pilot tone is canceled. For reaching a high channel separation
the TDA7540 offers an I2C-bus programmable roll-off adjustment, which is able to
compensate the low pass behavior of the tuner section. Within the compensation range an
adjustment to obtain at least 40dB channel separation is possible. The bits for this
adjustment are located together with the level gain adjustment in one byte. This gives the
possibility to perform an optimization step during the production of the car radio where the
channel separation and the header are trimmed.
In addition to that the FM signal can be inverted.
Deemphasis and highcut
The deemphasis low pass allows to choose between a time constant of 50µs/ 75μs
(DEEMP) and 25μs/37.5μs (DESFT). The highcut control range will be in both cases τ
2xτ
converted into a 5-bit word, which controls the low pass time constant between
τ
absolute voltage range between the VHCH- and VHCL-values.
The highcut function can be switched off by I
In AM mode (AMON = 1) the bits DEEMP and DESFT together with the AM corner
frequency bits (AMCF1...5) can be used as programmable AM frequency response. The
maximum corner frequency is defined by τ
19kHz PLL and pilot tone detector
The PLL has the task to lock on the 19kHz pilot tone during a stereo-transmission to allow a
correct demodulation. The included pilot tone-detector enables the demodulation if the pilot
tone reaches the selected pilot tone threshold V
available. The status of the detector output can be checked by reading the status byte of the
TDA7540N via I
Field strength control
The field strength input is used to control the highcut- and the stereoblend-function. In
addition the signal can be also used to control the noise blanker thresholds and as input for
the multipath detector.
Level-input and -gain
As level input for the stereo decoder is used the FSU voltage (pin22). Appling a capacitor at
FSTC (pin33) a desired time constant can by reached together with the internal resistor of
10k between FSU pin and FSTC pin.
In addition to that the LEVEL signal is low pass filtered internally in order to suppress
undesired high frequency modulation on the highcut- and stereoblend-function . The filter is
a combination of a 1
order switched capacitor low pass at 2.2kHz. The second stage is a programmable gain
stage to adapt the LEVEL signal internally . The gain is widely programmable in 8 steps
from 0dB to 4,7dB (step=0.67dB). These 3bits are located together with the Roll-Off bits in
the "Stereo decoder 8"-byte to simplify a possible adaptation during the production of the
car radio.
Deemp
Deemp
...3xτ
. Inside the highcut control range (between VHCH and VHCL) the LEVEL signal is
Deemp
2
C-bus or by reading the STEREO pin (pin 25).
. Thereby the resolution will remain always 5 bits independently of the
st
-order RC-low pass at 53kHz (working as anti-aliasing filter) and a 1
Deemp
2
C-bus .
PTHST
, the minimum is defined by 3xτ
. Two different thresholds are
TDA7540N
Deemp
HC
=
st
-