INTERSIL EL6204CW-T7A

EL6204
®
Data Sheet
March 1, 2004
Laser Driver Oscillator
Features
The EL6204 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
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 utility
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.
The EL6204 part is available in the space-saving 6-pin SOT23 package and is specified for operation from 0°C to +70°C.
FN7219.1
• User-selectable frequency from 60MHz to 600MHz
controlled with a single resistor
• User-specified amplitude from 10mAPK-PK to
100mAPK-PK controlled with a single resistor
• Auto turn-off threshold
• Soft edges for reduced EMI
• Small 6-pin SOT-23 package
Applications
• DVD players
• DVD-ROM drives
• CD-RW drives
• MO drives
• General purpose laser noise reduction
• Local oscillators
Pinout
Ordering Information
EL6204
(6-PIN SOT-23)
TOP VIEW
PART NUMBER
1
IOUT
RFREQ
6
2
VDD
GND2
5
3
GND1
RAMP
4
1
PACKAGE
TAPE & REEL PKG. DWG. #
EL6204CW-T7
6-Pin SOT-23
7” (3K pcs)
MDP0038
EL6204CW-T7A
6-Pin SOT-23
7” (250 pcs)
MDP0038
CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures.
1-888-INTERSIL or 321-724-7143 | 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.
EL6204
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 +70°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 = 5210Ω (FOSC = 350MHz), RAMP =
2540Ω (IOUT = 50mAP-P measured at 60MHz), 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 = 5.21kΩ, RAMP = 2.54kΩ
18.5
22
mA
ISLO
Supply Current Low Conditions
RFREQ = 30.5kΩ, RAMP = 12.7kΩ
4.75
mA
ISHI
Supply Current High Conditions
RFREQ = 3.05kΩ, RAMP = 1.27kΩ
32
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 = 5210Ω (FOSC = 350MHz), RAMP = 2540Ω (IOUT = 50mAP-P
measured at 60MHz), VOUT = 2.2V
PARAMETER
DESCRIPTION
CONDITIONS
MIN
TYP
MAX
UNIT
300
350
400
MHz
FOSC
Frequency Tolerance
Unit-unit frequency variation
FHIGH
Frequency Range High
RFREQ = 3.05kΩ
600
MHz
FLOW
Frequency Range Low
RFREQ = 30.5kΩ
60
MHz
TCOSC
Frequency Temperature Sensitivity
0°C to +70°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 = 30.5kΩ (FOSC = 60MHz), RAMP = 2540Ω (IOUT = 50mAP-P
measured at 60MHz), 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 = 5210Ω, VOUT = 2.2V
-4
mA
IOSHIGH
Offset Current @ 2.8V
RFREQ = 5210Ω, VOUT = 2.8V
-4.8
mA
IOSLOW
Offset Current @ 1.8V
RFREQ = 5210Ω, VOUT = 1.8V
-3.5
mA
IOUTP-P
Output Current Tolerance
Defined as one standard deviation
2
%
Duty Cycle
Output Push Time/Cycle Time
RFREQ = 5210Ω
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
EL6204
Pin Descriptions
PIN NAME
PIN TYPE
PIN DESCRIPTION
1
IOUT
Current output to laser diode
2
VDD
Positive power for laser driver (4.5V - 5.5V)
3
GND1
Chip ground pin (0V for output)
4
RAMP
Set pin for output current amplitude
5
GND2
Chip ground pin (0V for RFREQ, RAMP)
6
RFREQ
Set pin for oscillator frequency
Recommended Operating Conditions
VDD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5V ±10%
VOUT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2V - 3V
RFREQ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3kΩ (min)
RAMP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.25kΩ (min)
FOSC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .60-600MHz
IOUT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-100mAPK-PK
IOUT Control
VOUT
IOUT
Less than VCUTOFF
OFF
More than VCUTOFF
Normal Operation
3
EL6204
Typical Performance Curves
VDD = 5V, TA = 25°C, RL = 10Ω, RFREQ = 5.21kΩ, RAMP = 2.54kΩ, VOUT = 2.2V unless otherwise specified.
Frequency Distribution
Frequency Drift with Temperature
500
8
Typical
Production
Distortion
400
Measured from
-40°C to +85°C
7
Number of Parts
Number of Parts
6
300
200
5
4
3
2
100
1
Frequency (MHz)
90
78
66
Frequency vs 1 / RFREQ
700
700
Frequency=1824 * 1kΩ / RFREQ (MHz)
Frequency=1824 * 1kΩ / RFREQ (MHz)
600
500
500
Frequency (MHz)
600
400
300
400
300
200
200
100
100
0
0
0
5
10
15
20
25
30
35
0
0.05
0.1
RFREQ (kΩ)
0.15
0.2
0.25
0.3
0.35
1kΩ / RFREQ
Output Current vs RAMP
Output Current vs 1 / RAMP
180
180
160
IOUT PK-PK measured @60/350/600MHz
160
IOUT PK-PK measured @60/350/600MHz
140
(over-shoot included)
140
(over-shoot included)
Output Current (mA)
Output Current (mA)
54
Frequency TC (ppm/°C)
Frequency vs RFREQ
Frequency (MHz)
42
30
18
6
390
382
374
366
358
350
342
334
326
318
0
310
0
120
100
Amplitude PK-PK=127 * 1kΩ / RAMP (mA)
measured @60MHz
80
(over-shoot not included)
60
120
100
80
60
40
40
20
20
0
0
Amplitude PK-PK=
127 * 1kΩ / RAMP (mA)
measured @60MHz
(over-shoot not included)
0
2
4
6
8
RAMP (kΩ)
4
10
12
14
0
0.1
0.2
0.3
0.4
0.5
1kΩ / RAMP
0.6
0.7
0.8
0.9
EL6204
Typical Performance Curves
(Continued)
Supply Current vs RFREQ
Supply Current vs RAMP
25
35
Supply Current (mA)
Supply Current (mA)
30
20
15
25
20
15
10
0
0
0
5
10
15
20
25
30
35
0
5
10
15
RFREQ (kΩ)
Frequency vs Supply Voltage
25
30
35
Peak-to-Peak Output Current vs Supply Voltage
360
100
355
95
IOUT PK-PK (mA)
Frequency (MHz)
20
RAMP (kΩ)
350
345
90
85
340
4.4
4.6
4.8
5
5.2
5.4
80
4.4
5.6
4.6
4.8
Supply Voltage (V)
5
5.2
5.4
5.6
Supply Voltage (V)
Supply Current vs Supply Voltage
Frequency vs Temperature
21
400
380
Frequency (MHz)
Supply Current (mA)
20
19
360
340
18
320
17
4.4
4.6
4.8
5
5.2
Supply Voltage (V)
5
5.4
5.6
300
-50
0
50
Ambient Temperature (°C)
100
150
EL6204
Typical Performance Curves
(Continued)
Peak-to-Peak Output Current vs Temperature
Supply Current vs Temperature
95
30
90
25
Supply Current (mA)
80
75
70
20
15
65
60
-50
0
50
100
10
-50
150
0
Ambient Temperature (°C)
Output Current @ 60MHz
40mA
50
100
150
Ambient Temperature (°C)
Output Current @ 350MHz
4.0ns
40mA
RFREQ=30.3kΩ
RAMP=2.54kΩ
1.0ns
RFREQ=2.51kΩ
RAMP=2.54kΩ
Output Spectrum-Wideband
Output Current @ 600MHz
10
40mA
0.4ns
-10
Relative Amplitude (dB)
IOUT PK-PK (mA)
85
-30
-50
-70
RFREQ=3.03kΩ
RAMP=2.54kΩ
-90
340
344
348
352
Frequency (MHz)
6
356
360
EL6204
Block Diagram
IOUT
1
VDD
2
GND1
3
DRIVER
OSCILLATOR
REFERENCE
AND BIAS
AUTO SHUT-OFF
6
RFREQ
5
GND2
4
RAMP
Typical Application Circuit
Typical
ROM Laser
Driver
Gain
Setting
Resistor
EMI
Reduction
Filters
IAPC
BEAD
Frequency
Setting
Resistor
PNP
RFREQ
0.1µF
1
IOUT
RFREQ
6
2
VDD
GND2
5
3
GND1
RAMP
4
BEAD
Laser
Diode
+5V
Controller
4.7µF
0.1µF
RAMP
0.1µF
GND
RF
Blocking
Resistor
Main Board
Flex
~10mW
Amplitude
Setting
Resistor
Photo Diode
On Pickup
Laser Output
Power
Laser Output Power
Threshold Current
IAPC
0mW
0mA
~60mA
Laser Current
Oscillator Current
7
EL6204
Applications Information
Product Description
The EL6204 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 EL6204 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
EL6204 has the operating frequency from 60MHz to
600MHz and the output current from 10mAP-P to 100mAP-P.
The supply current is only 18.5mA for the output current of
50mAP-P at the operating frequency of 350MHz.
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,
8
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 EL6204'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 EL6204's local environment from
propagating to the modulation source, and it will keep
parasitic capacitance at the pin minimized.
EL6204
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.
The maximum power dissipation allowed in a package is
determined according to:
T JMAX - T AMAX
P DMAX = -------------------------------------------Θ JA
where
PDMAX = Maximum power dissipation in the package
L Series: 70Ω reactance at 300MHz
VS
0.1µF
Chip
TAMAX = Maximum ambient temperature
0.1µF
Chip
θJA = Thermal resistance of the package
GND
FIGURE 2. RECOMMENDED SUPPLY BYPASSING
Also important is circuit-board layout. At the EL6204'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.
RFREQ
× 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
Supply
Bypass
RAMP
GND
The supply current of the EL6204 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:
Sourcing Current Loop
Sinking Current Loop
Laser
Diode
FIGURE 3. OUTPUT CURRENT LOOPS
For the pushing current loop, the current flows through the
bypass capacitor, into the EL6204 supply pin, out the IOUT
pin to the laser, and from the laser back to the decoupling
capacitor. This loop should be small.
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.
Power Dissipation
With the high output drive capability, the EL6204 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.
9
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.
Package Power Dissipation vs Ambient Temperature
JEDEC JESD51-3 Low Effective Thermal Conductivity Test Board
0.6
0.5
Power Dissipation (W)
EL6204
TJMAX = Maximum junction temperature
+5V
488mW
0.4
6P
θ
JA
=
0.3
in
SO
T-2
25
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
EL6204
Package Power Dissipation vs Ambient Temperature
JEDEC JESD51-7 High Effective Thermal Conductivity Test Board
0.6
Power Dissipation (W)
0.5
543mW
θ
6Pi
n
SO
T23
23
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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