—10—

CXA1538M/N/S

Notes on Usage

1. VCO free run frequency adjustment method

As this IC has built-in oscillation capacitance, the oscillation frequency can be controlled with an external

resistor.

1) VCO Adjustment Method

Pin 4 is the stereo indicator and VCO check pin. Therefore, in stereo mode (when stereo indicator drive

Tr Q2 is switched on), pin 4 voltage lowers down, Q1 is cut off and VCO oscillation waveform can not be

seen. In AM mode as well, the oscillation waveform can not be seen as VCO turns off.

Adjust the free run frequency at 76 kHz ±50 Hz.

In this IC, tuner and MPX sections are directly connected. Therefore, free run frequency is not stable, being

affected by noise except in reception mode. For free run adjustment, input signals from either RF or IF.

(Input signal should be RF [Tuning frequency] or fo of the discriminator using IF (10.7 MHz) and input

more than 60 dBµ.)

2) How to Deal with pin 4 After Adjustment.

With the use of a stereo indicator.

R to prevent LED malfunction.

Without the use of a stereo indicator.

Turn pin 4 to open or connect to GND.

3) Control Resistor of VCO Oscillation Frequency

For the VCO control resistor of this iC, a carbon film resistor suffices.

For easier adjustment of temperature characteristics and VCO free run frequency, the following

combination is recommended.

27

28

10k

22k

Capacitor for decoupling

Q1

Q2

33k

about 180mVp-p

4

2.2k

4

OPEN

4

4

27

28

10k

22k

2.2k

R

>3V

4