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LA3410 View Datasheet(PDF) - SANYO -> Panasonic

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LA3410 Datasheet PDF : 13 Pages
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LA3410
6. Separation adjust
The separatin is adjusted by varying the main signal level in the composite signal. The main signal is applied to the post
amplifier input through amplifiers A1, A3. The input level in A3 is varied by internal resistor RA and external variable
resistor VR1. Therefore, the output main signal becomes 0 at VR1=0 and is maximized at VR1=. The separation is
presettable if VR1 is set to an adequate value. In this case, the VR1 value differs with each set ; X of VR1 is approxmately
150kwhen the ratio of the main signal and sub signal at the LA3410 input is 1 : 1 and the sub signal and pilot signal
are in phase. The separation, when preset, varies 30dB min. with the variations in the IC only considered. If the value
of capacitor C8 for DC cut is decreased, the separation gets worse at low frequencies.
7. Post amplifier oscillation when loaded capacitively (inductively)
If the post amplifier outputs (pins 4, 7) are loaded capacitively (inductively), oscillation may occur. When connecting
a low-pass filter to each of the outputs, an input resistor must be connected across the post amplifier output and the low-
pass filter and the wiring across these points must be made as short as possible.
8. Forced monaural mode
The following method is used to provide the forced monaural mode. In this case, VCO oscillation does not stop. The
above-mentioned VCO stop method is used to stop VCO oscillation.
· Connect pin 10 to GND through a resistor of 10k.
Other application circuit
1. How to improve the dynamic range of the post amplifier
The amplifier bias voltage is set low (3.0V) so that the LA3410 is capable of being operated from low voltage. If the
supply voltage is high, the following method can be used to extend the dynamic range.
Fig. 6 shows how to extend the dynamic range of the post amplifier. When RB is not used, the DC voltage across pins
4 and 7 is 3.0V. The DC volatage across pins 4 and 7 can be increased to extend the dynamic range of the post amplifier.
Pins 5, 6, being minus input pins of the post amplifier, are virtual GND
points. By connecting RB across pin 5 and GND and across pin 6 and GND,
the DC voltages on pins 4, 7 are obtained as follows :
3.0
RB+R1
RB
=3.0 (1+
R1
RB
)
3.0
RB+R2
RB
=3.0 (1+
R2
RB
)
The upper and lower loss voltages of the post amplifier are approximately
2V and 0.5V respectively. With these loss voltages considered, the voltages
on pins 4, 7 are set. For example, Figs. 11, 12 show how the dynamic range
is improved when the DC voltages on pins 4, 7 are set to approximately
5.2V with upper loss voltage 2V and lower loss voltage 0.5V of the post
amplifier considered. Fig. 11 shows the characteristic where no RB is con-
nected ; Fig. 12 shows the characteristic where RB=82kis connected.
2. Feedback resistance of post amplifier and total gain
Table 2 shows the feedback resistance of the post amplifier and the total gain. Fig. 13 shows the distortion vs. feedback
resistance characteristic. Figs. 14, 15 show the sample application circuits where R1 (R2) is 100kand 130krespec-
tively.
R1 (R2)k
62
82
100
130
150
180
C3 (C4)pF
750
620
510
390
330
270
Total gain [dB]
8.5
11
13
15
16
17..5
Output signal voltage typ [mV]
730
965
1177
1530
1766
2119
Table 2. R1 (R2), C3 (C4) – gain
No.1407–8/13
 

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