LA1776M Datasheet, PDF (26/41 Pages) Sanyo Semicon Device – Monolithic Linear IC Single-Chip Tuner IC for Car Radios

LA1776M
4. FM IF
4-1. Notes on FM SD and SD Adjustment
The FM station detection and IF counter buffer operate with the following elements.
FM S-meter
4V
20 kΩ
+
_SD
41
FM SD adj
38
37
AFC
SEEK = OFF
VCC
+
_AFC
2.7 V
2.7 + 0.6 V
-0.6 V
30 kΩ
VCC
SEEK = OF
+
_
Soft mute
44
mute on
1
2
+
_
+
mute AMP
_
33
mute d
mute ATT
58
23
IF conut
1
2
12
13
2
1
3
FM IF
IF conut
IF conut
200 kΩ 30 kΩ
2.5 V 5 V
ST IND
39
SD/ST
5V
The following conditions must be met for the station detection and IF counter buffer to operate.
(1) V24 > V41 - The S-meter voltage must be higher than the pin 41 voltage
(2) V33 < 0.7 V (Vbe) - The band muting function must not be operating.
(3) V23 = high - A high level (VDD) must be applied to pin 23 from a 51 kΩ resistor.
The figure below shows the relationships between the FM station detection, the IF counter buffer output, the S-
meter voltage, and the muting operation output.
Larger
V24
values
of R33
V38
S-meter
V33
Smaller values of R33
V26
5V
V23AC
V23DC
V33
over 0.7 V
SD as an
SD signal
OFF
IF
count
buffer
5V
OFF
V33
over 0.7 V
SD
SD
Mono
ON
ON ^Stereo
IF counter output off
2.5 V
0V
RDS and other types of SD detection can be used by switching these modes.
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