Five-Channel Dual CD/DVD Laser Driver for Ultra Combo Drives
CXA2680ER
Sony developed the CXA2680ER as a dedicated laser driver
IC that increases the number of channels to five to support
increased bit depth recording strategies. The CXA2680ER
also adds a DVD modulator amplitude switching function
to the CXA2640ER for use in dual drive systems and fea-
tures high linear velocity to follow the actuators used in
conventional CD-R/RW drives.
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CD system total maximum drive current: 370 mA
DVD system total maximum drive current: 320 mA
Rise/fall time: 1 ns
Support for strategy in all 5 channels
Read channel low noise: 1.5 nA/√Hz
High-frequency modulator frequency accuracy:
<
±10%
Built-in DVD modulator amplitude switching func-
tion
Support for a variety of timing signals
Achieving both Higher
Output and Higher Speed
While both an increased output transient
waveform speed and an increased maxi-
mum output drive current are required to
achieve increased linear velocities,
increasing the maximum output drive
current required increasing the size of the
output transistors. However, increasing the
size of the output transistors leads to
delays in the output transient waveform.
Despite this tradeoff relationship, the
CXA2680ER achieves both of the follow-
ing output current performance levels.
• CD system total maximum drive current:
370 mA (figure 1)
(V
CC
= 5 V, V
OP
= 2.5 V, T = 150
°C)
• DVD system total maximum drive
current: 320 mA (figure 2)
(V
CC
= 5 V, V
OP
= 3 V, T = 150
°C)
Thus this device can supply the required
maximum output drive current even
under severe operating conditions for both
CD and DVD. Furthermore, in the
CXA2680ER, Sony optimized the output
transient waveforms to have both higher
speed and a minimal amount of overshoot
by including a built-in waveform shaping
circuit. This allows this device to support
×8-speed
DVD recording.
Support for a Variety of
Timing Signals
The CXA2680ER provides both differen-
tial inputs (LVDS/LVPECL) for higher
speeds and single-ended inputs (3.3 V
CMOS/TTL).
Read Channel Low Noise
Sony’s painstaking low-noise design
efforts to achieve the signal-to-noise
ratio required for higher linear speeds
achieved a noise level of 1.5 nA/√Hz (at
20 MHz, 35 mA, 20 mA p-p).
Small Package with Improved
Heat Dissipation
The CXA2680ER is provided in a 32-pin
VQFN (4.8
×
4.8 mm) miniature package
that can contribute to pickup miniaturiza-
tion through reductions in the mounting
area.
Not only is the package size noteworthy,
but this package can also increase the
efficiency with which heat is dissipated,
since it allows the heat sink to be con-
nected with silicon grease to the die pads,
which are exposed at the package surface.
Since this prevents heat from escaping
through the PWB to the laser diode, PWBs
using this device are easy on the laser
diode. This also allows the IC to be con-
nected at the rear surface.
High-Frequency Modulator
Frequency Accuracy
In high-frequency modulator, which is
used to reduce noise during playback,
interference between the return light from
the disc and the laser beam due to varia-
tions in frequency causes noise to be
aggravated. The CXA2680ER cancels
frequency variations depending on the
internal resistance caused by VCO that has
the emitter junction multivibrator, thus
allowing noise to reduce.
DVD System Modulator
Amplitude Switching
Function
V
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This function allows applications to set a
modulator amplitude value that is
optimal for the DVD media used.
It’s been five years since I first
started designing laser driver ICs,
and by now I have a good idea of
what is required in laser driver ICs.
I strongly recommend that you
look into the CXA2680ER, which
was developed based on this ac-
cumulated know-how.
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SONY [ SONY CORPORATION ]
