LA1787M Datasheet, PDF (13/54 Pages) Sanyo Semicon Device – Single-Chip Tuner IC for Car Radios

Continued from preceding page.
Pin No.
Function
34
AGC
35
QD output
36
QD input
37
V_REF
38
FM SD ADJ
39
Keyed AGC
AM stereo buffer
LA1787M
Description
Equivalent circuit
0.1µF _VREF
R1
VCC
C
•The resistor R₁ determines the
width of the band muting function.
Increasing the value of R₁
narrows the band.
Reducing the value of R₁ widens
the band.
•Null voltage
When tuned, the voltage between
pins 34 and 37, V_{34 – 37}, will be 0 V.
The band muting function turns
on when |V_{34 – 37}| ≥ 0.7 V.
V₃₇ = 4.9 V
R2
37
36
35
34
VCC
Quadrature
detector
HOLE
DET
3pF
1kΩ
A 130-µA current flows from pin
38 and, in conjunction with the
external resistance R, determines
the comparison voltage.
The keyed AGC operates when
the voltage created by dividing the
pin 24 S-meter output voltage by
the 6.4 and 3.6 kΩ resistors
becomes lower than the voltage
determined by the resistor
between pin 39 and ground.
This pin also is used as the AM
stereo IF buffer pin.
IF limitter amplifier
R
SD ADJ
38
Band
muting
A13577
130µA
SD
Comparator
24
S-meter
A13578
S-meter
Comparator
KEYED
AGC
+
–
1.3V
VCC
24
6.4kΩ
3.6kΩ
39
90µA
AM IF out
50pF _150Ω
A13579
Continued on next page.
No. 6655-13/54