DATASHEET

EL6206
®
Data Sheet
June 10, 2004
Laser Driver Oscillator
Features
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 pickups.
• Low power dissipation
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.
FN7340
• User-selectable frequency from 100MHz to 600MHz
controlled with a single resistor
• User-specified amplitude from 10mAPK-PK to 100mAPK
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
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 powerefficient, it has less harmonic content, and it has an auto
shut-off feature activated at 1.1V.
Ordering Information
EL6206CW-T7
5-Pin SOT23
7” (3K pcs)
MDP0038
The part is available in the space-saving 5-pin SOT23
package. It is specified for operation from 0°C to +85°C.
EL6206CW-T7A
5-Pin SOT23
7” (250 pcs)
MDP0038
PART NUMBER
PACKAGE
TAPE & REEL PKG. DWG. #
Pinout
EL6206
(5-PIN SOT23)
TOP VIEW
1
VDD
2
GND
3
IOUT
1
RFREQ
5
RAMP
4
CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures.
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EL6206
Absolute Maximum Ratings (TA = 25°C)
Voltages Applied to:
VDD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.5V to +6.0V
IOUT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.5V to +6.0V
RFREQ, RAMP . . . . . . . . . . . . . . . . . . . . . . . . . -0.5V to +6.0V
Operating Ambient Temperature Range . . . . . . . . . . . 0°C to +85°C
Maximum Junction Temperature . . . . . . . . . . . . . . . . . . . . . . +150°C
Storage Temperature Range . . . . . . . . . . . . . . . . . .-65°C to +150°C
Output Current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100mAPK-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: TJ = TC = TA
Supply & Reference Voltage Characteristics VDD = +5V, TA = 25°C, RL = 10Ω, RFREQ = 3.5kΩ (FOSC = 550MHz), RAMP = 2540Ω
(IOUT = 50mAP-P measured at 100MHz), VOUT = 2.2V
PARAMETER
DESCRIPTION
CONDITIONS
MIN
TYP
UNIT
5.5
V
PSOR
Power Supply Operating Range
ISO
Supply Current Disabled
VOUT < VCUTOFF
550
750
µA
ISTYP
Supply Current Typical Conditions
RFREQ = 3.5kΩ, RAMP = 2.54kΩ
22
TBD
mA
ISLO
Supply Current Low Conditions
RFREQ = 18.2kΩ, RAMP = 12.7kΩ
6
mA
VFREQ
Voltage at RFREQ Pin
1.27
V
VRAMP
Voltage on RAMP Pin
1.27
V
VCUTOFF
Monitoring Voltage of IOUT Pin
Oscillator Characteristics
4.5
MAX
1.1
1.4
V
VDD = +5V, TA = 25°C, RL = 10Ω, RFREQ = 3.5kΩ (FOSC = 550MHz), RAMP = 2540Ω (IOUT = 50mAP-P
measured at 100MHz), VOUT = 2.2V
PARAMETER
DESCRIPTION
CONDITIONS
MIN
TYP
MAX
UNIT
TBD
550
TBD
MHz
FOSC
Frequency Tolerance
Unit-unit frequency variation
FLOW
Frequency Range Low
RFREQ = 18.2kΩ
100
MHz
TCOSC
Frequency Temperature Sensitivity
-40°C to +85°C ambient
50
ppm/°C
PSRROSC
Frequency Change ∆F/F
VDD from 4.5V to 5.5V
1
%
Driver Characteristics
VDD = +5V, TA = 25°C, RL = 10Ω, RFREQ = 18.2kΩ (FOSC = 100MHz), RAMP = 2540Ω (IOUT = 50mAP-P
measured at 100MHz), VOUT = 2.2V
PARAMETER
DESCRIPTION
CONDITIONS
MIN
TYP
MAX
UNIT
AMPHIGH
Amplitude Range High
RAMP = 1.27kΩ
100
mAP-P
AMPLOW
Amplitude Range Low
RAMP = 12.7kΩ
10
mAP-P
IOSNOM
Offset Current @ 2.2V
RFREQ = 3.5kΩ, VOUT = 2.2V
TBD
mA
IOSHIGH
Offset Current @ 2.8V
RFREQ = 3.5kΩ, VOUT = 2.8V
TBD
mA
IOSLOW
Offset Current @ 1.8V
RFREQ = 3.5kΩ, VOUT = 1.8V
TBD
mA
IOUTP-P
Output Current Tolerance
Defined as one standard deviation
2
%
Duty Cycle
Output Push Time/Cycle Time
RFREQ = 3.5kΩ
43
%
PSRRAMP
Amplitude Change of Output ∆I/I
VDD from 4.5V to 5.5V
-54
dB
TON
Auto Turn-on Time
Output voltage step from 0V to 2.2V
15
µs
TOFF
Auto Turn-off Time
Output voltage step from 2.2V to 0V
0.5
µs
IOUTN
Output Current Noise Density
RFREQ = 5210Ω, measured @ 10MHz
2.5
nA/√Hz
2
EL6206
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
Recommended Operating Conditions
VDD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5V ±10%
VOUT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2V - 3V
RFREQ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3kΩ (min)
RAMP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.25kΩ (min)
FOSC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .100-600MHz
IOUT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-100mAPK-PK
IOUT Control
VOUT
IOUT
Less than VCUTOFF
OFF
More than VCUTOFF
Normal Operation
Typical Performance Curves
VDD = 5V, TA = 25°C, RL = 10Ω, RFREQ = 3.5kΩ, RAMP = 2.54kΩ, VOUT = 2.2V unless otherwise specified.
FREQUENCY vs RFREQ
FREQUENCY vs 1 / RFREQ
700
700
Frequency=1824 * 1kΩ / RFREQ (MHz)
600
600
500
500
FREQUENCY (MHz)
FREQUENCY (MHz)
Frequency=1824 * 1kΩ / RFREQ (MHz)
400
300
200
100
400
300
200
100
0
0
0
5
10
15
20
25
30
35
0
0.05
RFREQ (kΩ)
0.1
0.15
0.2
1kΩ / RFREQ
Block Diagram
VDD
1
GND
2
IOUT
3
3
DRIVER
OSCILLATOR
5
RFREQ
AUTO SHUT-OFF
REFERENCE
AND BIAS
4
RAMP
0.25
0.3
0.35
EL6206
Typical Application Circuit
TYPICAL
ROM LASER
DRIVER
EMI
REDUCTION
SUPPLY
FILTER
GAIN
SETTING
RESISTOR
+5V
BEAD
4.7µF
0.1µF
PNP
IAPC
VDD1
2
GND
3
IOUT
RFREQ
5
RFREQ
BEAD
CONTROLLER
GND
0.1µF
EMI
REDUCTION
FILTER
MAIN BOARD
1
FLEX
RAMP
4
RAMP
Laser Diode
PHOTO DIODE
AMPLITUDE
SETTING
RESISTOR
ON PICKUP
~10mW
LASER OUTPUT
POWER
LASER OUTPUT
POWER
THRESHOLD
CURRENT
IAPC
0mW
0mA
~60mA
LASER CURRENT
OSCILLATOR CURRENT
4
FREQUENCY
SETTING
RESISTOR
EL6206
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 10mAP-P to 100mAP-P.
The supply current is only 22mA for the output current of
50mAP-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 pushingcurrent 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.
RAMP and RFREQ Value Setting
The laser should always have a forward current during
operation. This will prevent the laser voltage from collapsing,
5
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 RAMP and
RFREQ resistors must be determined experimentally. A good
starting point is to take a value of RAMP for a peak-to-peak
current amplitude less than the minimum laser threshold
current and a value of RFREQ for an output current close to a
sinusoidal wave form (refer to the proceeding performance
curves).
RAMP and RFREQ Pin Interfacing
Figure 1 shows an equivalent circuit of pins associated with
the RAMP and RFREQ resistors. VREF is roughly 1.27V for
both RAMP and RFREQ. The RAMP and RFREQ 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.
+
VREF
-
PIN
FIGURE 1. RAMP AND RFREQ PIN INTERFACE
External voltage sources can be coupled to the RAMP and
RFREQ 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 highfrequency noise of the EL6206's local environment from
propagating to the modulation source, and it will keep
parasitic capacitance at the pin minimized.
EL6206
Supply Bypassing and Grounding
The resistance of bypass-capacitors and the inductance of
bonding wires prevent perfect bypass action, and 150mVP-P
noise on the power lines is common. There needs to be a
lossy bead inductance and secondary bypass on the supply
side to control signals from propagating down the wires.
Figure 2 shows the typical connection.
L Series: 70Ω reactance at 300MHz
EL6206
0.1µF
Chip
T JMAX – T AMAX
P DMAX = -------------------------------------------Θ JA
where
PDMAX = Maximum Power Dissipation in the Package
TJMAX = Maximum Junction Temperature
+5V
VS
The maximum power dissipation allowed in a package is
determined according to:
TAMAX = Maximum Ambient Temperature
0.1µF
Chip
θJA = Thermal Resistance of the Package
GND
The supply current of the EL6206 depends on the peak-topeak output current and the operating frequency which are
determined by resistors RAMP and RFREQ. The supply
current can be predicted approximately by the following
equation:
FIGURE 2. RECOMMENDED SUPPLY BYPASSING
Also important is circuit-board layout. At the EL6206's
operating frequencies, even the ground plane is not lowimpedance. High frequency current will create voltage drops
in the ground plane. Figure 3 shows the output current loops.
× 1kΩ- + --------------------------------30mA × 1kΩ- + 0.6mA
-----------------------------------------I SUP = 31.25mA
R AMP
R FREQ
The power dissipation can be calculated from the following
equation:
P D = V SUP × I SUP
RFREQ
SUPPLY
BYPASS
RAMP
SOURCING CURRENT LOOP
SINKING CURRENT LOOP
GND
LASER
DIODE
FIGURE 3. OUTPUT CURRENT LOOPS
Here, VSUP is the supply voltage. Figures 4 and 5 provide a
convenient way to see if the device will overheat. The
maximum safe power dissipation can be found graphically,
based on the package type and the ambient temperature. By
using the previous equation, it is a simple matter to see if PD
exceeds the device's power derating curve. To ensure proper
operation, it is important to observe the recommended
derating curve shown in Figures 4 and 5. A flex circuit may
have a higher θJA, and lower power dissipation would then
be required.
For the pushing current loop, the current flows through the
bypass capacitor, into the EL6206 supply pin, out the IOUT
pin to the laser, and from the laser back to the decoupling
capacitor. This loop should be small.
JEDEC JESD51-3 LOW EFFECTIVE THERMAL
CONDUCTIVITY TEST BOARD
0.6
Power Dissipation
With the high output drive capability, the EL6206 is possible
to exceed the 125°C “absolute-maximum junction
temperature” under certain conditions. Therefore, it is
important to calculate the maximum junction temperature for
the application to determine if the conditions need to be
modified for the oscillator to remain in the safe operating
area.
6
POWER DISSIPATION (W)
0.5
For the pulling current loop, the current flows into the IOUT
pin, out of the ground pin, to the laser cathode, and from the
laser diode back to the IOUT pin. This loop should also be
small.
488mW
0.4
θ
5Pi
n
JA
=
25
0.3
SO
T2
3
6°
C/
W
0.2
0.1
0
0
25
50
75 85
100
125
150
AMBIENT TEMPERATURE (°C)
FIGURE 4. PACKAGE POWER DISSIPATION VS AMBIENT
TEMPERATURE
EL6206
JEDEC JESD51-7 HIGH EFFECTIVE THERMAL
CONDUCTIVITY TEST BOARD
0.6
POWER DISSIPATION (W)
0.5
543mW
θ
5Pi
n
SO
T2
23
3
0°
C/
W
JA
=
0.4
0.3
0.2
0.1
0
0
25
50
75 85
100
125
150
AMBIENT TEMPERATURE (°C)
FIGURE 5. PACKAGE POWER DISSIPATION VS AMBIENT
TEMPERATURE
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