LA1787M Datasheet, PDF (33/54 Pages) Sanyo Semicon Device – Single-Chip Tuner IC for Car Radios

LA1787M
However, when testing this stop sensitivity, note that when checking the waveform on the IF count buffer output
(pin 23), there are cases, such as that shown below, where current in the test system may be seen as flowing to
ground and cause oscillation that causes the IF count buffer output to go to the output state.
F.E.
IF
IF buffer
amp
5V
0.022 µF
Test system capacitance
The 10.7 MHz feeds back through ground.
Fig. 18
A12081
• FM Muting control pin (pin 47) (R47: 30 kΩ variable resistor)
The –3 dB limiting sensitivity can be adjusted with R47.
FM Soft Muting (1)
R47 = 7.5 kΩ
15 kΩ
Fig.19
DET out
10 kΩ
20 kΩ
Noise
Antenna input — dBµ
• FM muting attenuation adjustment (pin 58)
The muting attenuation can be switched between the three levels of –20, –30, and –40 dB by the resistor inserted
between pin 58 and ground. (Note that the exact values depend on the total tuner gain.)
The noise convergence with no input is determined by the pin 58 voltage.
58
100Ω R58
R58
Open
200 kΩ
30 kΩ
Mute ATT
–20 dB
–30 dB
–40 dB
A11764
33
The attenuation can be set by making R33 smaller as listed
in the table above.
R33
Fig. 20
A11765
No. 6655-33/54