1
FN7340
CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures.
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Intersil (and design) is a registered trademark of Intersil Americas Inc.
Copyright Intersil Americas Inc. 2004. All Rights Reserved. Elantec is a registered trademark of Elantec Semiconductor, Inc.
All other trademarks mentioned are the property of their respective owners.
EL6206
Laser Driver Oscillator
The EL6206 is a push-pull oscillator
used to reduce laser noise. It uses the
standard interface to existing ROM
controllers. The frequency and amplitude are each set with a
separate resistor connected to ground. The tiny package and
harmonic reduction allow the part to be placed close to a
laser with low RF emissions. An auto turn-off feature allows it
to easily be used on combo CD-RW plus DVD-ROM pick-
ups.
One external resistor sets the oscillator frequency. Another
external resistor sets the oscillator amplitude. If the APC
current is reduced such that the average laser voltage drops
to less than 1.1V, the output and oscillator are disabled,
reducing power consumption to a minimum.
The current drawn by the oscillator consists of a small bias
current, plus the peak output amplitude in the positive cycle.
In the negative cycle the oscillator subtracts peak output
amplitude from the laser APC current.
This part is pin-compatible to the EL6201. It is superior to the
EL6201 in several ways: It has up to 100mA output
capability, it is faster (up to 600MHz), it is more power-
efficient, it has less harmonic content, and it has an auto
shut-off feature activated at 1.1V.
The part is available in the space-saving 5-pin SOT23
package. It is specified for operation from 0
C to +85
C.
Pinout
EL6206
(5-PIN SOT23)
TOP VIEW
Features
Low power dissipation
User-selectable frequency from 100MHz to 600MHz
controlled with a single resistor
User-specified amplitude from 10mA
PK-PK
to 100mA
PK
controlled with a single resistor
Auto turn-off threshold
Soft edges for reduced EMI
Small 5-pin SOT23 package
Applications
DVD players
DVD-ROM drives
CD-RW drives
MO drives
General purpose laser noise reduction
1
2
3
5
4
VDD
RFREQ
GND
IOUT
RAMP
Ordering Information
PART NUMBER
PACKAGE
TAPE & REEL PKG. DWG. #
EL6206CW-T7
5-Pin SOT23
7" (3K pcs)
MDP0038
EL6206CW-T7A
5-Pin SOT23
7" (250 pcs)
MDP0038
Data Sheet
June 10, 2004
2
Absolute Maximum Ratings
(T
A
= 25C)
Voltages Applied to:
V
DD
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.5V to +6.0V
I
OUT
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.5V to +6.0V
R
FREQ
, R
AMP
. . . . . . . . . . . . . . . . . . . . . . . . . -0.5V to +6.0V
Operating Ambient Temperature Range . . . . . . . . . . . 0C to +85C
Maximum Junction Temperature . . . . . . . . . . . . . . . . . . . . . . +150C
Storage Temperature Range . . . . . . . . . . . . . . . . . . -65C to +150C
Output Current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100mA
PK-PK
Power Dissipation (max) . . . . . . . . . . . . . . . . . . . . . . . . See Curves
CAUTION: Stresses above those listed in "Absolute Maximum Ratings" may cause permanent damage to the device. This is a stress only rating and operation of the
device at these or any other conditions above those indicated in the operational sections of this specification is not implied.
IMPORTANT NOTE: All parameters having Min/Max specifications are guaranteed. Typical values are for information purposes only. Unless otherwise noted, all tests
are at the specified temperature and are pulsed tests, therefore: T
J
= T
C
= T
A
Supply & Reference Voltage Characteristics
V
DD
= +5V, T
A
= 25C, R
L
= 10
, R
FREQ
= 3.5k
(F
OSC
= 550MHz), R
AMP
= 2540
(I
OUT
= 50mA
P-P
measured at 100MHz), V
OUT
= 2.2V
PARAMETER
DESCRIPTION
CONDITIONS
MIN
TYP
MAX
UNIT
PSOR
Power Supply Operating Range
4.5
5.5
V
I
SO
Supply Current Disabled
V
OUT
< V
CUTOFF
550
750
A
I
STYP
Supply Current Typical Conditions
R
FREQ
= 3.5k
,
R
AMP
= 2.54k
22
TBD
mA
I
SLO
Supply Current Low Conditions
R
FREQ
= 18.2k
, R
AMP
= 12.7k
6
mA
V
FREQ
Voltage at R
FREQ
Pin
1.27
V
V
RAMP
Voltage on RAMP Pin
1.27
V
V
CUTOFF
Monitoring Voltage of I
OUT
Pin
1.1
1.4
V
Oscillator Characteristics
V
DD
= +5V, T
A
= 25C, R
L
= 10
, R
FREQ
= 3.5k
(F
OSC
= 550MHz), R
AMP
= 2540
(I
OUT
= 50mA
P-P
measured at 100MHz), V
OUT
= 2.2V
PARAMETER
DESCRIPTION
CONDITIONS
MIN
TYP
MAX
UNIT
F
OSC
Frequency Tolerance
Unit-unit frequency variation
TBD
550
TBD
MHz
F
LOW
Frequency Range Low
R
FREQ
= 18.2k
100
MHz
TC
OSC
Frequency Temperature Sensitivity
-40C to +85C ambient
50
ppm/C
PSRR
OSC
Frequency Change
F/F
V
DD
from 4.5V to 5.5V
1
%
Driver Characteristics
V
DD
= +5V, T
A
= 25C, R
L
= 10
, R
FREQ
= 18.2k
(F
OSC
= 100MHz), R
AMP
= 2540
(I
OUT
= 50mA
P-P
measured at 100MHz), V
OUT
= 2.2V
PARAMETER
DESCRIPTION
CONDITIONS
MIN
TYP
MAX
UNIT
AMP
HIGH
Amplitude Range High
R
AMP
= 1.27k
100
mA
P-P
AMP
LOW
Amplitude Range Low
R
AMP
= 12.7k
10
mA
P-P
IOS
NOM
Offset Current @ 2.2V
R
FREQ
= 3.5k
,
V
OUT
= 2.2V
TBD
mA
IOS
HIGH
Offset Current @ 2.8V
R
FREQ
= 3.5k
,
V
OUT
= 2.8V
TBD
mA
IOS
LOW
Offset Current @ 1.8V
R
FREQ
= 3.5k
,
V
OUT
= 1.8V
TBD
mA
I
OUTP-P
Output Current Tolerance
Defined as one standard deviation
2
%
Duty Cycle
Output Push Time/Cycle Time
R
FREQ
= 3.5k
43
%
PSRR
AMP
Amplitude Change of Output
I/I
V
DD
from 4.5V to 5.5V
-54
dB
T
ON
Auto Turn-on Time
Output voltage step from 0V to 2.2V
15
s
T
OFF
Auto Turn-off Time
Output voltage step from 2.2V to 0V
0.5
s
IOUT
N
Output Current Noise Density
R
FREQ
= 5210
,
measured @ 10MHz
2.5
nA/
Hz
EL6206
3
Recommended Operating Conditions
V
DD
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5V 10%
V
OUT
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2V - 3V
R
FREQ
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3k
(min)
R
AMP
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.25k
(min)
F
OSC
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .100-600MHz
I
OUT
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-100mA
PK-PK
Typical Performance Curves
Block Diagram
Pin Descriptions
PIN NAME
PIN TYPE
PIN DESCRIPTION
1
VDD
Positive power for laser driver (4.5V - 5.5V)
2
GND
Chip ground pin (0V)
3
IOUT
Current output to laser diode
4
RAMP
Set pin for output current amplitude
5
RFREQ
Set pin for oscillator frequency
I
OUT
Control
V
OUT
I
OUT
Less than V
CUTOFF
OFF
More than V
CUTOFF
Normal Operation
V
DD
= 5V, T
A
= 25C, R
L
= 10
, R
FREQ
= 3.5k
, R
AMP
= 2.54k
, V
OUT
= 2.2V unless otherwise specified.
FREQ
UENCY (
M
Hz)
0
200
400
500
600
700
R
FREQ
(k
)
0
FREQUENCY vs R
FREQ
5
15
25
35
10
20
30
100
300
Frequency=1824 * 1k
/ R
FREQ
(MHz)
FREQ
UENCY (
M
Hz)
0
200
400
500
600
700
1k
/ R
FREQ
0
FREQUENCY vs 1 / R
FREQ
0.05
0.15
0.25
0.35
0.1
0.2
0.3
100
300
Frequency=1824 * 1k
/ R
FREQ
(MHz)
1
2
3
5
4
AUTO SHUT-OFF
DRIVER
REFERENCE
AND BIAS
OSCILLATOR
V
DD
GND
I
OUT
R
FREQ
R
AMP
EL6206
4
Typical Application Circuit
1
2
3
5
4
VDD1
RFREQ
GND
IOUT
RAMP
CONTROLLER
FREQUENCY
SETTING
RESISTOR
EMI
REDUCTION
SUPPLY
FILTER
GAIN
SETTING
RESISTOR
TYPICAL
ROM LASER
DRIVER
Laser Diode
PHOTO DIODE
BEAD
+5V
GND
4.7F
AMPLITUDE
SETTING
RESISTOR
0.1F
PNP
BEAD
0.1F
EMI
REDUCTION
FILTER
MAIN BOARD
ON PICKUP
FLEX
LASER OUTPUT
POWER
LASER CURRENT
0mW
~10mW
0mA
~60mA
OSCILLATOR CURRENT
LASER OUTPUT
POWER
THRESHOLD
CURRENT
IAPC
RFREQ
RAMP
IAPC
EL6206
5
Applications Information
Product Description
The EL6206 is a solid state, low-power, high-speed laser
modulation oscillator with external resistor-adjustable
operating frequency and output amplitude. It is designed to
interface easily to laser diodes to break up optical feedback
resonant modes and thereby reduce laser noise. The output
of the EL6206 is composed of a push-pull current source,
switched alternately at the oscillator frequency. The output
and oscillator are automatically disabled for power saving
when the average laser voltage drops to less than 1.1V. The
EL6206 has the operating frequency from 100MHz to
600MHz and the output current from 10mA
P-P
to 100mA
P-P
.
The supply current is only 22mA for the output current of
50mA
P-P
at the operating frequency of 550MHz.
Theory of Operation
A typical semiconductor laser will emit a small amount of
incoherent light at low values of forward laser current. But
after the threshold current is reached, the laser will emit
coherent light. Further increases in the forward current will
cause rapid increases in laser output power. A typical
threshold current is 35mA and a typical slope efficiency is
0.7mW/mA.
When the laser is lasing, it will often change its mode of
operation slightly, due to changes in current, temperature, or
optical feedback into the laser. In a DVD-ROM, the optical
feedback from the moving disk forms a significant noise
factor due to feedback-induced mode hopping. In addition to
the mode hopping noise, a diode laser will roughly have a
constant noise level regardless of the power level when a
threshold current is exceeded.
The oscillator is designed to produce a low noise oscillating
current that is added to the external DC current. The
effective AC current is to cause the laser power to change at
the oscillator frequency. This change causes the laser to go
through rapid mode hopping. The low frequency component
of laser power noise due to mode hopping is translated up to
sidebands around the oscillator frequency by this action.
Since the oscillator frequency can be filtered out of the low
frequency read and serve channels, the net result is that the
laser noise seems to be reduced. The second source of
laser noise reduction is caused by the increase in the laser
power above the average laser power during the pushing-
current time. The signal-to-noise ratio (SNR) of the output
power is better at higher laser powers because of the almost
constant noise power when a threshold current is exceeded.
In addition, when the laser is off during the pulling-current
time, the noise is also very low.
R
AMP
and R
FREQ
Value Setting
The laser should always have a forward current during
operation. This will prevent the laser voltage from collapsing,
and ensure that the high frequency components reach the
junction without having to charge the junction capacitance.
Generally it is desirable to make the oscillator currents as
large as possible to obtain the greatest reduction in laser
noise. But it is not a trivial matter to determine this critical
value. The amplitude depends on the wave shape of the
oscillator current reaching the laser junction.
If the output current is sinusoidal, and the components in the
output circuit are fixed and linear, then the shape of the
current will be sinusoidal. But the amount of current reaching
the laser junction is a function of the circuit parasitics. These
parasitics can result in a resonant increase in output
depending on the frequency due to the junction capacitance
and layout. Also, the amount of junction current causing
laser emission is variable with frequency due to the junction
capacitance. In conclusion, the sizes of the R
AMP
and
R
FREQ
resistors must be determined experimentally. A good
starting point is to take a value of R
AMP
for a peak-to-peak
current amplitude less than the minimum laser threshold
current and a value of R
FREQ
for an output current close to a
sinusoidal wave form (refer to the proceeding performance
curves).
R
AMP
and R
FREQ
Pin Interfacing
Figure 1 shows an equivalent circuit of pins associated with
the R
AMP
and R
FREQ
resistors. V
REF
is roughly 1.27V for
both R
AMP
and R
FREQ
. The R
AMP
and R
FREQ
resistors
should be connected to the non-load side of the power
ground to avoid noise pick-up. These resistors should also
return to the EL6206's ground very directly to prevent noise
pickup. They also should have minimal capacitance to
ground. Trimmer resistors can be used to adjust initial
operating points.
External voltage sources can be coupled to the R
AMP
and
R
FREQ
pins to effect frequency or amplitude modulation or
adjustment. It is recommended that a coupling resistor of 1k
be installed in series with the control voltage and mounted
directly next to the pin. This will keep the inevitable high-
frequency noise of the EL6206's local environment from
propagating to the modulation source, and it will keep
parasitic capacitance at the pin minimized.
-
+
PIN
V
REF
FIGURE 1. R
AMP
AND R
FREQ
PIN INTERFACE
EL6206
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