LA1787M Просмотр технического описания (PDF) - ON Semiconductor

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LA1787M

Monolithic Linear IC Single-Chip Tuner IC for Car Radios

ON Semiconductor 

Continued from preceding page.

Pin No.

Function

34

AGC

35

QD output

36

QD input

37

VREF

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, V34 – 37, will be 0 V.

The band muting function turns

on when |V34 – 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

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