– 66 –
CXA2550M/N
• LASER POWER CONTROL (LPC)
The RF level is stabilized by attaching an offset to the APC V
L
and controlling the laser power in sync with the
RF level fluctuations.
The RF O and RF I levels are compared and the larger of the two is smoothed by the RFTC's external CR.
This signal is then compared with the reference level.
The laser power is controlled by attaching an offset to V
L
according to the results of comparison with the
reference level.
Set the reference level to 670mV. (center voltage reference)
When the reference level is changed, connect the external resistor to the AGCVTH pin (Pin 1). The reference
level can be lowered by connecting the resistor between Pin 1 and the center output voltage or between Pin
20 and V
CC
.
The AGCCONT pin (pin 18) is used to switch the level of the laser power control circuit; OFF, ON (laser power
limit of 30%) and ON (laser power limit of 50%)
Note) For the laser power limit, 50% is recommended for PD IC; 30% for LC.
Notes on Operation
1. Power supply
The CXA2550M/N can be used either at dual power supply or single power supply. The table below shows the
connection of power supply for each case.
2. RF amplifier
In this circuit, the IC internal phase compensation value is set so as to support the voltage output-type pickup.
Therefore, when the current output-type pickup is used, the capacitance of optical pickup and leads etc. are
attached to PD1 and PD2 pins and oscillation may occur.
3. laser power control
The RF level is stabilized by attaching an offset to the APC V
L
and controlling the laser power in sync with the
RF level fluctuations. Therefore, use this circuit in the state where the focus servo is applied.
The laser life is shortened by increasing the laser power when the less light is reflected from the disc. It is
recommended that the typical laser power value is set lower to maintain the laser life.
Take care of the laser maximum ratings when using the laser power control circuit.
AGCCONT
H (V
CC
)
M (VC or OPEN)
L (V
EE
)
LPC
OFF
ON
ON
LPC limit
—
30%
50%
V
L
variable range
Approximately 1.27V
Approximately 1.27V ± 350mV
Approximately 1.27V ± 570mV
Dual power supply
Single power supply
V
CC
+power supply
Power supply
V
EE
–power supply
GND
VC
GND
OPEN
Summary of Contents for PV420S
Page 1: ...SERVICE MANUAL PV420S WWW BBK RU ...
Page 72: ... 69 CXD3068Q Block Diagram ...
Page 73: ... 70 CXD3068Q Pin Configuration ...
Page 122: ... 119 CXD3068Q Timing Chart 1 3 ...
Page 123: ... 120 CXD3068Q Timing Chart 1 4 ...
Page 124: ... 121 CXD3068Q Timing Chart 1 5 ...
Page 129: ... 126 CXD3068Q Timing Chart 2 1 ...
Page 130: ... 127 CXD3068Q Block Diagram 2 2 ...
Page 131: ... 128 CXD3068Q Timing Chart 2 3 ...
Page 134: ... 131 CXD3068Q Timing Chart 2 6 ...
Page 138: ... 135 CXD3068Q VCO C Mode Fig 3 3 Access Flow Chart Using VCO Control ...
Page 140: ... 137 CXD3068Q Block Diagram 4 1 ...
Page 143: ... 140 CXD3068Q Timing Chart 4 4 ...
Page 147: ... 144 CXD3068Q Fig 4 6 a Auto Focus Flow Chart Fig 4 6 b Auto Focus Timing Chart ...
Page 148: ... 145 CXD3068Q Fig 4 7 a 1 Track Jump Flow Chart Fig 4 7 b 1 Track Jump Timing Chart ...
Page 149: ... 146 CXD3068Q Fig 4 8 a 10 Track Jump Flow Chart Fig 4 8 b 10 Track Jump Timing Chart ...
Page 150: ... 147 CXD3068Q Fig 4 9 a 2N Track Jump Flow Chart Fig 4 9 b 2N Track Jump Timing Chart ...
Page 151: ... 148 CXD3068Q Fig 4 10 a Fine Search Flow Chart Fig 4 10 b Fine Search Timing Chart ...
Page 152: ... 149 CXD3068Q Fig 4 11 a M Track Move Flow Chart Fig 4 11 b M Track Move Timing Chart ...
Page 157: ... 154 CXD3068Q Fig 4 15 CD TEXT Data Timing Chart ...
Page 162: ... 159 CXD3068Q Fig 5 3a Fig 5 3b ...
Page 196: ... 193 CXD3068Q Description of Data Readout ...
Page 200: ... 197 CXD3068Q ...
Page 201: ... 198 CXD3068Q ...
Page 202: ... 199 CXD3068Q ...
Page 207: ... 204 CXD3068Q Package Outline Unit mm ...
Page 208: ...This data sheet has been made from recycled paper to help protect the environment 205 ...
