CXA1538 Sony Corporation, CXA1538 Datasheet - Page 10

• Manufacturer Part Number: CXA1538
• Description: FM STEREO/AM RADIO
• Manufacturer: Sony Corporation

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
2) How to Deal with pin 4 After Adjustment.
3) Control Resistor of VCO Oscillation Frequency
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.)
With the use of a stereo indicator.
Without the use of a stereo indicator.
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.
4
4
OPEN
2.2k
4
27
V
CC
=3V
10k
22k
27
Q1
Turn pin 4 to open or connect to GND.
28
10k
22k
Q2
—10—
28
4
When V
R to prevent LED malfunction.
Capacitor for decoupling
CC
33k
is 3 V or more, insert a bypass resistance
about 180mVp-p
4
V
CC
2.2k
R
V
CC
3V
CXA1538M/N/S