LA1787M Datasheet, PDF (12/54 Pages) Sanyo Semicon Device – Single-Chip Tuner IC for Car Radios

Continued from preceding page.
Pin No.
Function
LA1787M
Description
30
Noise canceller input
31
AM/FM detector output
Pin 30 is the noise canceller input.
The input impedance is 50 kΩ.
Pin 31 is the AM and FM detector
output
In FM mode, this is a low-
impedance output.
In AM mode, the output
impedance is 10 kΩ.
To improve the low band
separation, use a coupling
capacitor of over 10 µF.
Equivalent circuit
VCC
FM
detector
output
31
10kΩ
VCC
AM
detector
1µF
+
30
Noise
canceller
50kΩ
4.2V
VCC
A13574
FM S-meter output block
MRC AC input block
32
IF S-meter output and MRC
DC input
Adjust the external 1-kΩ resistor
to attenuate the MRC AC input
and control the circuit.
33
Mute drive output
•The muting time constant is
determined by an external RC
circuit as described below.
Attack time: T_A = 10 kΩ × C1
Release time: T_R = 50 kΩ × C1
•Noise convergence adjustment
The noise convergence can be
adjusted when there is no input
signal by inserting a resistor
between pin 33 and ground.
•Muting off function
Ground pin 33 through a 4-kΩ
resistor.
10kΩ
32
+
1µF
1kΩ
MRC input
C1
+
0.1µF
A13575
SEEK
OFF
VCC
33
50kΩ
10kΩ
MUTE
AMP.
SOFT HOLE Band
MUTE DET muting
50kΩ
SD circuit
A13576
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