SA1787 Datasheet, PDF (9/19 Pages) Silan Microelectronics Joint-stock – SINGLE-CHIP TUNER IC FOR CAR RADIOS

SA1787
Pin No.
37
Pin Name
VREF
38
SD ADJ
Key AGC
39
AM Buffer
40
VCC
41
HCC Cap
42
AM L.C.
43
Pilot Det
44
IF AGC
45
IF OUT
AM ANT D
46
WB-AGC
47
Mute ADJ
48
AGC Bypass
57
RF AGC
50
IF Bypass
51
FM IF IN
I/O
O
V37 = 4.9V
Descriptions
The SD comparison voltage is determined with the external resistance
I/O
R and the current flow at pin 38.
When the voltage of V24*0.36 becomes lower than the voltage
determined by the resistor between pin 39 and ground, the keyed AGC
I/O
is turned on.
The pin39 is also used as the AM stereo IF buffer pin.
I/O VCC for FMIF and AM NC MPX
With pin 41 external capacitor
O
High-Cut frequency characteristics are set.
Frequency characteristics of unnecessary voice band of 100Hz or less
is changed to produce the clear sound in the AM mode.
Note: The LC capacitor must be connected between the pin42 and
I/O VCC
This is because the detector circuit operates referenced to VCC.
AM LC f characteristic:
fC = 1/2π*50 k Ω* C
Inserting a 1-MΩ resistor between pin 43 and VCC causes the forced
O
mono mode.
Time constant changeover at Seek switch.
• Reception
　Time constant depends on the external capacitor of pin 44:
O
C44*300kΩ
• Seek
　Time constant is:
C44*10Ω
O
The IF amplifier load
I46 = 6mA (maximum)
O
An antenna damping current for AM pin diode drive output
Muting on level can be changed by modify the value of the external
I
resistor
RF AGC rectifier capacitor。
O
Determination of the distortion radio during low-frequency modulation:
Increasing C48 and C57 :
DistortionÆimproved
ResponseÆslow
O
Reducing C48 and C57 :
DistortionÆworse
ResponseÆquick
Choose IF bypass capacitor to GND to prevent the limiter AMP from
I
osillation
I
FM 10.7M AMP input
HANGZHOU SILAN MICROELECTRONICS CO.,LTD
Http://www.silan.com.cn
REV:1.0
2008.08.29
Page 9 of 19