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EL6208
Data Sheet July 23, 2003 FN7374
Dual Push-Pull Laser Driver Oscillator
The EL6208 is a dual push-pull oscillator used to reduce laser noise in twin laser diodes. It uses the standard interface to existing ROM controllers. The frequency and amplitude are both 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 activates the oscillator only when the APC current is applied. 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 waveform is filtered to reduce EMI emissions. The EL6208 operates from a signal +5V supply. Power consumption is very low. The EL6208 part is available in the space-saving 6-pin SOT-23 package and is specified for operation from 0C to +70C.
Features
* Low power dissipation * 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
* CD-DVD ROM drives
Pinout
EL6208 (6-PIN SOT-23) TOP VIEW
VDD 1 RFREQ 2 RAMP 3 6 IOUT2 5 GND 4 IOUT1
Ordering Information
PART NUMBER EL6208CW-T7 EL6208CW-T7A PACKAGE 6-Pin SOT-23 6-Pin SOT-23 TAPE & REEL 7" (3K pcs) 7" (250 pcs) PKG. DWG. # MDP0038 MDP0038
1
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 (c) Intersil Americas Inc. 2003. All Rights Reserved. Elantec is a registered trademark of Elantec Semiconductor, Inc. All other trademarks mentioned are the property of their respective owners.
EL6208
Absolute Maximum Ratings (TA = 25C)
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 . . . . . . . . . . . 0C to +70C Maximum Junction Temperature . . . . . . . . . . . . . . . . . . . . . . +150C Storage Temperature Range . . . . . . . . . . . . . . . . . .-65C to +150C Output Current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100mAPK-PK Power Dissipation (max) . . . . . . . . . . . . . . . . . . . . . . . . See Curves
Recommended Operating Conditions
VDD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5V 10% VOUT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2V - 3V RFREQ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3K (min) RAMP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.25k (min) FOSC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .60-600MHz IOUT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-100mAPK-PK
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
PARAMETER PSOR ISO ISTYP ISLO ISHI VFREQ VRAMP VCUTOFF DESCRIPTION Power Supply Operating Range Supply Current Disabled Supply Current Typical Conditions Supply Current Low Conditions Supply Current High Conditions Voltage at RFREQ Pin Voltage on RAMP Pin Monitoring Voltage of IOUT Pin
VDD = +5V, TA = 25C, RL = 10, RFREQ = 5210 (FOSC = 360MHz), RAMP = 2540 (IOUT = 50mAP-P measured at 60MHz), VOUT = 2.2V CONDITIONS MIN 4.5 VOUT < VCUTOFF RFREQ = 5.21k, RAMP = 2.54k RFREQ = 18.2k, RAMP = 12.7k RFREQ = 3.3k, RAMP = 1.27k 280 20 5.4 36.8 1.27 1.27 1.1 1.4 TYP MAX 5.5 440 23 UNIT V A mA mA mA V V V
Oscillator Characteristics
PARAMETER FOSC FHIGH FLOW TCOSC PSRROSC
VDD = +5V, TA = 25C, RL = 10, RFREQ = 5210 (FOSC = 360MHz), RAMP = 2540 (IOUT = 50mAP-P measured at 60MHz), VOUT = 2.2V CONDITIONS Unit-unit frequency variation RFREQ = 3.3k RFREQ = 18.2k 0C to +70C ambient VDD from 4.5V to 5.5V MIN 310 TYP 358 566 100 50 1 MAX 400 UNIT MHz MHz MHz ppm/C %
DESCRIPTION Frequency Tolerance Frequency Range High Frequency Range Low Frequency Temperature Sensitivity Frequency Change F/F
Driver Characteristics
PARAMETER AMPHIGH AMPLOW IOSNOM IOSHIGH IOSLOW IOUTP-P Duty Cycle PSRRAMP
VDD = +5V, TA = 25C, RL = 10, RFREQ = 30.5k (FOSC = 60MHz), RAMP = 2540 (IOUT = 50mAP-P measured at 60MHz), VOUT = 2.2V DESCRIPTION CONDITIONS RAMP = 1.27k RAMP = 12.7k RFREQ = 5210, VOUT = 2.2V RFREQ = 5210, VOUT = 2.8V RFREQ = 5210, VOUT = 1.8V Defined as one standard deviation RFREQ = 5210 VDD from 4.5V to 5.5V MIN TYP 100 10 -4 -4.8 -3.5 2 43 -54 MAX UNIT mAP-P mAP-P mA mA mA % % dB
Amplitude Range High Amplitude Range Low Offset Current @ 2.2V Offset Current @ 2.8V Offset Current @ 1.8V Output Current Tolerance Output Push Time/Cycle Time Amplitude Change of Output I/I
2
EL6208
Driver Characteristics
PARAMETER TON TOFF IOUTN VDD = +5V, TA = 25C, RL = 10, RFREQ = 30.5k (FOSC = 60MHz), RAMP = 2540 (IOUT = 50mAP-P measured at 60MHz), VOUT = 2.2V (Continued) DESCRIPTION Auto Turn-on Time Auto Turn-off Time Output Current Noise Density CONDITIONS Output voltage step from 0V to 2.2V Output voltage step from 2.2V to 0V RFREQ = 5210, measured @ 10MHz MIN TYP 15 0.5 2.5 MAX UNIT s s nA/Hz
Pin Descriptions
PIN NAME 1 2 3 4 5 6 PIN TYPE VDD RFREQ RAMP IOUT1 GND1 IOUT2 PIN DESCRIPTION Positive power for laser driver (4.5V - 5.5V) Set pin for oscillator frequency Set pin for output current amplitude Current output to laser diode Chip ground pin (0V for output) Current output to laser diode
IOUT Control
VOUT Less than VCUTOFF More than VCUTOFF IOUT OFF Normal Operation
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EL6208 Typical Performance Curves
VDD = 5V, TA = 25C, RL = 10, RFREQ = 5.21k, RAMP = 2.54k, VOUT = 2.2V unless otherwise specified.
500 400 300 200 100 0 TYPICAL PRODUCTION DISTORTION 8 7 NUMBER OF PARTS 6 5 4 3 2 1 320 328 336 344 352 360 368 376 384 392 400 6 18 30 42 54 66 78 0.3 0.8 90 0.35 0.9 0 MEASURED FROM -40C TO +85C
NUMBER OF PARTS
FREQUENCY (MHz)
FREQUENCY TC (ppm/C)
FIGURE 1. FREQUENCY DISTRIBUTION
FIGURE 2. FREQUENY DRIFT with TEMPERATURE
700 FREQ = 1824 * 1k / RFREQ (MHz) 600 FREQUENCY (MHz) FREQUENCY (MHz) 500 400 300 200 100 0 0 5 10 15 20 25 30 35 RFREQ (k)
700 FREQ = 1824 * 1k / RFREQ (MHz) 600 500 400 300 200 100 0 0 0.05 0.1 0.15 0.2 0.25 1k / RFREQ
FIGURE 3. FREQUENCY vs RFREQ
FIGURE 4. FREQUENCY vs 1 / RFREQ
180 160 OUTPUT CURRENT (mA) 140 120 100 80 60 40 20 0 0 2 4 6 8 10 12 14 RAMP (k) OUTPUT CURRENT (mA) IOUT PK-PK MEASURED @60/350/600MHz (OVER-SHOOT INCLUDED) AMPLITUDE PK-PK = 127 * 1k / RAMP (mA) MEASURED @60MHz (OVER-SHOOT NOT INCLUDED)
180 AMPLITUDE PK-PK = 127 * 1k / RAMP (mA) MEASURED 140 @60MHz (OVER-SHOOT NOT INCLUDED) 120 160 100 80 60 40 20 0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 1k / RAMP IOUT PK-PK MEASURED @60/350/600MHz (OVER-SHOOT INCLUDED)
FIGURE 5. OUTPUT CURRENT vs RAMP
FIGURE 6. OUTPUT CURRENT vs 1 / RAMP
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EL6208 Typical Performance Curves (Continued)
VDD = 5V, TA = 25C, RL = 10, RFREQ = 5.21k, RAMP = 2.54k, VOUT = 2.2V unless otherwise specified.
50 SUPPLY CURRENT (mA) 40 30 RAMP=2.54k 20 10 RAMP=20k 0 0 5 10 15 RFREQ (k) 20 25 30 RAMP=5k RAMP=10k RAMP=1k SUPPLY CURRENT (mA) 45 40 35 30 25 20 15 10 5 0 0 5 10 15 RAMP (k) 20 25 30 RFREQ=10k RFREQ=30k RFREQ=5.21k RFREQ=20k RFREQ=2.9k
FIGURE 7. SUPPLY CURRENT vs RFREQ
FIGURE 8. SUPPLY CURRENT vs RAMP
360
100
FREQUENCY (MHz)
IOUT PK-PK (mA)
355
95
350
90
345
85
340 4.4
4.6
4.8
5
5.2
5.4
5.6
80 4.4
4.6
4.8
5
5.2
5.4
5.6
SUPPLY VOLTAGE (V)
SUPPLY VOLTAGE (V)
FIGURE 9. FREQUENCY vs SUPPLY VOLTAGE
FIGURE 10. PEAK-TO-PEAK OUTPUT CURRENT vs SUPPLY VOLTAGE
21 SUPPLY CURRENT (mA)
400 380 360 340 320 300 -50
20
19
18
17 4.4
FREQUENCY (MHz)
4.6
4.8
5
5.2
5.4
5.6
0
50
100
150
SUPPLY VOLTAGE (V)
AMBIENT TEMPERATURE (C)
FIGURE 11. SUPPLY CURRENT vs SUPPLY VOLTAGE
FIGURE 12. FREQUENCY vs TEMPERATURE
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EL6208 Typical Performance Curves (Continued)
VDD = 5V, TA = 25C, RL = 10, RFREQ = 5.21k, RAMP = 2.54k, VOUT = 2.2V unless otherwise specified.
95 SUPPLY CURRENT (mA) 0 50 100 150 90 IOUT PK-PK (mA) 85 80 75 70 65 60 -50 30
25
20
15
10 -50
0
50
100
150
AMBIENT TEMPERATURE (C)
AMBIENT TEMPERATURE (C)
FIGURE 13. PEAK-TO-PEAK OUTPUT CURRENT vs TEMPERATURE
FIGURE 14. SUPPLY CURRENT vs TEMPERATURE
40mA
5ns
40mA
1ns
RFREQ=30.3k RAMP=2.54k
RFREQ=5.21k RAMP=2.54k
FIGURE 15. OUTPUT CURRENT @60MHz
FIGURE 16. OUTPUT CURRENT @350MHz
10 40mA 0.5ns RELATIVE AMPLITUDE (dB) -10 -30 -50 -70 -90 340
RFREQ=3.03k RAMP=2.54k
344
348
352
356
360
FREQUENCY (MHz)
FIGURE 17. OUTPUT CURRENT @600MHz
FIGURE 18. OUTPUT SPECTRUM - WIDEBAND
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EL6208 Block Diagram
VDD 1 OSCILLATOR DRIVER 6 IOUT1 AUTO SHUTOFF
RFREQ 2
5 GND
RAMP 3
DRIVER
4 IOUT1
Typical Application Diagram
EMI REDUCTION FILTERS IAPC2 TWIN ROM LASER DRIVER
PNP
BEAD +5V RFREQ 2 RFREQ LASER POWER CONTROL 4.7F PNP AMPLITUDE SETTING RESISTOR BEAD 0.1F 0.1F RAMP 3 RAMP IOUT1 4 GND 5 1 VDD IOUT2 6
BEAD LASER DIODE LASER DIODE
GAIN SETTING RESISTORS
FREQUENCY SETTING RESISTOR
0.1F
GND
PHOTO DIODE
MAIN BOARD
FLEX
ON PICKUP
Typical Waveforms
~10mW LASER OUTPUT POWER THRESHOLD CURRENT IAPC 0mW 0mA ~60mA LASER CURRENT
LASER OUTPUT POWER
OSCILLATOR CURRENT
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EL6208 Applications Information
Product Description
The EL6208 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 EL6208 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 EL6208 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. 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).
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 Pin Interfacing
Figure 19 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 EL6208'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 19. RAMP AND RFREQ PIN INTERFACE
RAMP and RFREQ Value Setting
The laser should always have a forward current during operation. This will prevent the laser voltage from collapsing,
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 EL6208's local environment from propagating to the modulation source, and it will keep parasitic capacitance at the pin minimized.
Supply Bypassing and Grounding
The resistance of bypass-capacitors and the inductance of bonding wires prevent perfect bypass action, and 150mVP-P
8
EL6208
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 20 shows the typical connection.
L SERIES: 70 REACTANCE AT 300MHz VS 0.1F CHIP GND EL6208 +5V 0.1F CHIP
where: PDMAX = Maximum power dissipation in the package TJMAX = Maximum junction temperature TAMAX = Maximum ambient temperature JA = Thermal resistance of the package The supply current of the EL6208 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:
31.25mA x 1k 30mA x 1k I SUP = ------------------------------------------ + ---------------------------------- + 0.6mA R FREQ R AMP
FIGURE 20. RECOMMENDED SUPPLY BYPASSING
Also important is circuit-board layout. At the EL6208's operating frequencies, even the ground plane is not lowimpedance. High frequency current will create voltage drops in the ground plane. Figure 21 shows the output current loops.
RFREQ RAMP SUPPLY BYPASS SOURCING CURRENT LOOP
The power dissipation can be calculated from the following equation:
P D = V SUP x I SUP
GND
SINKING CURRENT LOOP
LASER DIODE
FIGURE 21. OUTPUT CURRENT LOOPS
For the pushing current loop, the current flows through the bypass capacitor, into the EL6208 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.
Here, VSUP is the supply voltage. Figures 22 and 23 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 22 and 23. A flex circuit may have a higher JA, and lower power dissipation would then be required.
JEDEC JESD51-3 LOW EFFECTIVE THERMAL CONDUCTIVITY TEST BOARD 0.6 POWER DISSIPATION (W) 0.5 0.4 0.3 0.2 0.1 0 0 25 50 75 85 100 125 150 AMBIENT TEMPERATURE (C) 488mW
6Pi n SO =2 T23 56 C/ W
JA
Power Dissipation
With the high output drive capability, the EL6208 is possible to exceed the 125C "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. The maximum power dissipation allowed in a package is determined according to:
T JMAX - T AMAX P DMAX = ------------------------------------------- JA
FIGURE 22. PACKAGE POWER DISSIPATION vs AMBIENT TEMPERATURE
9
EL6208
JEDEC JESD51-7 HIGH EFFECTIVE THERMAL CONDUCTIVITY TEST BOARD 0.6 POWER DISSIPATION (W) 0.5 543mW 0.4 0.3 0.2 0.1 0 0 25 50 75 85 100 125 150 AMBIENT TEMPERATURE (C)
6-
JA
Pi n SO =2 T30 23 C/ W
FIGURE 23. PACKAGE POWER DISSIPATION vs AMBIENT TEMPERATURE
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Intersil products are sold by description only. Intersil Corporation reserves the right to make changes in circuit design, software and/or specifications at any time without notice. Accordingly, the reader is cautioned to verify that data sheets are current before placing orders. Information furnished by Intersil is believed to be accurate and reliable. However, no responsibility is assumed by Intersil or its subsidiaries for its use; nor for any infringements of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Intersil or its subsidiaries.
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