LA1787M Datasheet, PDF (39/54 Pages) Sanyo Semicon Device – Single-Chip Tuner IC for Car Radios

LA1787M
• Notes on AM SD (pin 26) and the SD adjustment pin
SD and the IF buffer are operated by comparing the S-meter level (V24) and the 5 V reference voltage as shown in
figure 36.
S-meter
VCC
50 µA
Comparator
+
–
AM IF
IF buff amp.
50 pF
55
100 kΩ
24
0.47 µF
23
26
100 kΩ
51 kΩ
0.022 µF
5V
IF buffer SD
Seek
5V
Fig. 36
A12085
Figure 37 shows the relationship between the AM SD, the IF count buffer, and the S-meter.
V24PIN
V55
V26
Larger
values
of R55
S-meter
Smaller values of R55
V23AC
SD on
OFF
IF buffer on
V23DC
5V
Pin 55: AM SD adjustment pin
Fig. 37
0V
A11760
No. 6655-39/54