LA1787M Datasheet, PDF (31/54 Pages) Sanyo Semicon Device – Single-Chip Tuner IC for Car Radios

LA1787M
2. FM IF
• Notes on the FM SD and SD adjustment
The figure below presents an overview of the FM SD and the IF count buffer.
Band
muting
HOLE
CLET
S-meter
4.9V
R
+
–
R
+
–
R
Muting
drive
output
STEREO
IND
+
–
39 24
33
IF count buffer
FM IF
23
IF count output
2.5V 5V
Fig. 13
26
5V
SD
STEREO/MONO
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Figure 14 shows the relationship between the FM SD, the IF count buffer output, the S-meter, and the muting drive
output.
Larger
V24
values
of R33
V38
S-meter
V33
Smaller values of R33
V26
5V
V23AC
V33
over 0.7 V
On as an
SD signal
V23DC
OFF
IF count
buffer
5V
OFF
V33
over 0.7 V
SD
SD
ON
ON ^Stereo
IF counter output off
Mono
0.7 V
2.5 V
0V
RDS and other types of SD detection can be used by switching these modes.
New LA1784M functionality: For stereo input (when the V26 pin voltage is 0.7 V),
when this pin is shorted to ground (0.1 V or lower)
the IC will operate in forced mono mode.
Fig. 14
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No. 6655-31/54