513
Optical disc ICs
Preservo amplifier for CD players
BA6386K
The BA6386K is a preservo amplifier for CD players. By using this paired with a ROHM DSP, a servo and main signal
system can be configured with few external components and low power consumption.
FApplications
CD players
FFeatures
1) Internal RF AGC circuits.
2) Internal APC circuit.
3) Internal auto asymmetry circuit.
4) Internal disc defect detector.
5) Internal focus protect function against disc defects.
FAbsolute maximum ratings (Ta = 25_C)
FRecommended operating conditions (Ta = 25_C)
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Optical disc ICs BA6386K
Block diagram
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Optical disc ICs BA6386K
Pin descriptions
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Optical disc ICs BA6386K
FElectrical characteristics (unless otherwise noted, Ta = 25_C and VCC = 2.5V)
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Optical disc ICs BA6386K
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Optical disc ICs BA6386K
Measurement circuit
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Optical disc ICs BA6386K
Circuit operation
(1) RF amplifier, FOK comparator
RFO is shifted downwards from VB by 0.9V.
However, the resistance between pins 23 and 24 is set
to 20kΩ and if this resistance is changed, use external
components to adjust the shift back to 0.9V. Have the
feedback resistance 10kΩ or greater.
If the DC component of RF rises 0.3V, then FOK be-
comes high.
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Optical disc ICs BA6386K
(2) FE amplifier and focus search
The voltage for focus search is obtained by the charging
and discharging of the capacitor attached to pin 8. The
charging current is I/10 and the discharging current is I.
The FEO output amplitude (VSERCH) at this time is deter-
mined by the formula given below.
VSERCH = ±I 15kΩ 2 (VB reference)
Moreover , from Fig. 3, I can be approximated by the for-
mula given below.
Set R1 1 so that I becomes 2 µA or greater . Apply biasing
to the focus error signal from pin 29. If no adjustment oc-
curs, pin 29 = VB.
The timing charts when the focus loop turns ON or OFF
are given on the next page.
VCC*1.4
65k)R11
I = 1
3
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Optical disc ICs BA6386K
(1) LOOP ON timing
When FOK turns high, the fall of FE’ is detected and the
FOCUS LOOP turns ON.
(2) LOOP OFF timing
After FOK turns low, the FOCUS LOOP turns OFF after
the delay T (s) shown in the figure below.
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Optical disc ICs BA6386K
(3) APC block and AGC block
The initial setting for V1 is 1.2V . When PL-BL (the RF AC
amplitude) exceeds a certain value (VAGC), then AGC low-
ers V1 and suppresses the laser power. The value of VAGC
is Iagc 20k, where Iagc is set by the formula given be-
low.
When R18 = 10kΩ, Iagc = 50µA and VAGC = 1V.
When defect turns high, Tr1 turns OFF.
1.2
1.4kR18
Iagc =
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Optical disc ICs BA6386K
(4) DET block
When defect is high, the bottom hold (long) charging cur-
rent is 50µA. The scratch depth (VSC) can be adjusted by
changing the resistance at pin 9.
The peak hold voltage will not go below (GND ) 0.9V)
and the bottom hold voltage will not go below (VCC *
0.9V).
1.2
R9)200
VSC = 4k
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Optical disc ICs BA6386K
Application example
External dimensions (Units: mm)
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Optical disc ICs BA6386K
Electrical characteristics curves
