TDA7540N STMicroelectronics, TDA7540N Datasheet - Page 33

• 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

TDA7540N
4.3.3
4.3.4
used to increase the PEAK voltage. Offset and gain of this circuit are programmable in 3
steps (NBDTH) of the stereo decoder-byte (the first step turns off the detector).
Multipath-level
To react on high repetitive spikes caused by a Multipath-situation, the discharge-time of the
PEAK voltage can be decreased depending on the voltage-level at Pin MPout. There are
two ways to do this. One way is to switch on the linear influence of the Multipath-Level on the
PEAK-signal . In this case the discharge slew rate is 1V/ms
activate a function, which switches to the 18k discharge if the Multipath-Level is below 2.5V.
If multipath influence on noise blanker is switched ON than MPF bit has to be set to 0.
1)
AM Mode of Noise Blanker
The TDA7540N offers an AM audio noise blanker too.
If the AM noise blanker is used the AM audio delay filter and the AM audio filter must be
switched on. It is not recommented to use the AM noise blanker without to use the AMIF
noiseblanker inside the tuner.
The noise blanker is activated if the spike is bigger than a fixed threshold
In order to blank the whole spike in AM mode the hold time of the S&H circuit is much longer
than in FM mode (640µs -1.2ms).
Functional description of the multipath-detector
Using the internal Multipath-Detector the audible effects of a multipath condition can be
minimized. A multipath-condition is detected by rectifying the 19kHz spectrum in the
fieldstrength signal. An external capacitor is used to define the attack- and decay-times (see
block diagram,
capacitor of about 47nF. Using this configuration an external adaptation to the user's
requirement is possible without affecting the "normal" fieldstrength input (LEVEL) for the
stereo decoder.
To keep the old value of the Multipath Detector during an AF-jump, the MP-Hold switch can
disconnect the external capacitor. This switch is controlled directly by the AFS-Pin.
Selecting MPION the channel separation is automatically reduced during a multipath
condition according to the voltage appearing at the MP_OUT-pin.
Programming
To obtain a good multipath performance an adaptation is necessary. Therefore the gain of
the first 19kHz-bandpass is programmable in two steps (MPG), the gain of the second
19kHz-bandpass is programmable in four steps (MPBPG) and the rectifier gain is
programmable in four steps(MPRG). Please note that the frequency of the first multipath
bandpass (MPF) must be set to 19kHz! The attack- and decay-times can be set by the
external capacitor value and the multipath detector charge current MPCC.
Quality detector
The TDA7540N offers a quality detector output, which gives a voltage representing the FM-
reception conditions. To calculate this voltage the MPX-noise and the multipath-detector
output are summed according to the following formula:
The slew rate is measured with R
Figure
16). The MP_OUT-pin is used as detector-output connected to a
Discharge
=infinite and V
MPout
=2.5V
1)
. The second possibility is to
Functional description
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