EL6208 ® Data Sheet July 23, 2003 Dual Push-Pull Laser Driver Oscillator Features 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. • 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 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 0°C to +70°C. FN7374 • 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 PACKAGE TAPE & REEL PKG. DWG. # EL6208CW-T7 6-Pin SOT-23 7” (3K pcs) MDP0038 EL6208CW-T7A 6-Pin SOT-23 7” (250 pcs) MDP0038 PART NUMBER 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 © 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 = 25°C) Recommended Operating Conditions 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 VDD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5V ±10% VOUT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2V - 3V RFREQ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3KΩ (min) RAMP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.25kΩ (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 VDD = +5V, TA = 25°C, RL = 10Ω, RFREQ = 5210Ω (FOSC = 360MHz), 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 280 440 µA ISTYP Supply Current Typical Conditions RFREQ = 5.21kΩ, RAMP = 2.54kΩ 20 23 mA ISLO Supply Current Low Conditions RFREQ = 18.2kΩ, RAMP = 12.7kΩ 5.4 mA ISHI Supply Current High Conditions RFREQ = 3.3kΩ, RAMP = 1.27kΩ 36.8 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 = 360MHz), RAMP = 2540Ω (IOUT = 50mAP-P measured at 60MHz), VOUT = 2.2V PARAMETER DESCRIPTION CONDITIONS MIN TYP MAX UNIT 310 358 400 MHz FOSC Frequency Tolerance Unit-unit frequency variation FHIGH Frequency Range High RFREQ = 3.3kΩ 566 MHz FLOW Frequency Range Low RFREQ = 18.2kΩ 100 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 2 EL6208 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 (Continued) PARAMETER DESCRIPTION CONDITIONS MIN TYP MAX UNIT 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 Pin Descriptions PIN NAME PIN TYPE PIN DESCRIPTION 1 VDD 2 RFREQ 3 RAMP Set pin for output current amplitude 4 IOUT1 Current output to laser diode 5 GND1 Chip ground pin (0V for output) 6 IOUT2 Current output to laser diode Positive power for laser driver (4.5V - 5.5V) Set pin for oscillator frequency IOUT Control VOUT IOUT Less than VCUTOFF OFF More than VCUTOFF Normal Operation 3 EL6208 Typical Performance Curves VDD = 5V, TA = 25°C, RL = 10Ω, RFREQ = 5.21kΩ, RAMP = 2.54kΩ, VOUT = 2.2V unless otherwise specified. 400 8 TYPICAL PRODUCTION DISTORTION 7 NUMBER OF PARTS NUMBER OF PARTS 500 300 200 100 MEASURED FROM -40°C TO +85°C 6 5 4 3 2 FREQUENCY (MHz) 90 78 66 54 FIGURE 2. FREQUENY DRIFT with TEMPERATURE 700 700 FREQ = 1824 * 1kΩ / RFREQ (MHz) FREQ = 1824 * 1kΩ / RFREQ (MHz) 600 FREQUENCY (MHz) 600 500 400 300 200 500 400 300 200 100 100 0 0 0 5 10 15 20 25 30 0 35 0.05 0.1 0.15 0.2 0.25 0.3 0.35 1kΩ / RFREQ RFREQ (kΩ) FIGURE 4. FREQUENCY vs 1 / RFREQ FIGURE 3. FREQUENCY vs RFREQ 180 180 IOUT PK-PK MEASURED @60/350/600MHz (OVER-SHOOT INCLUDED) 140 120 AMPLITUDE PK-PK = 127 * 1kΩ / RAMP (mA) MEASURED @60MHz (OVER-SHOOT NOT INCLUDED) 100 80 AMPLITUDE PK-PK = 127 * 1kΩ / RAMP (mA) MEASURED 140 @60MHz (OVER-SHOOT NOT INCLUDED) 120 160 OUTPUT CURRENT (mA) 160 OUTPUT CURRENT (mA) 42 FREQUENCY TC (ppm/°C) FIGURE 1. FREQUENCY DISTRIBUTION FREQUENCY (MHz) 30 18 6 0 400 392 384 376 368 360 352 344 336 328 0 320 1 60 40 100 80 60 20 20 0 0 0 2 4 6 8 10 12 RAMP (kΩ) FIGURE 5. OUTPUT CURRENT vs RAMP 4 14 IOUT PK-PK MEASURED @60/350/600MHz 40 (OVER-SHOOT INCLUDED) 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 1kΩ / RAMP FIGURE 6. OUTPUT CURRENT vs 1 / RAMP 0.9 EL6208 Typical Performance Curves (Continued) VDD = 5V, TA = 25°C, RL = 10Ω, RFREQ = 5.21kΩ, RAMP = 2.54kΩ, VOUT = 2.2V unless otherwise specified. 50 45 RFREQ=2.9kΩ SUPPLY CURRENT (mA) SUPPLY CURRENT (mA) 40 RAMP=1kΩ 40 30 RAMP=2.54kΩ 20 RAMP=10kΩ RAMP=5kΩ 10 35 RFREQ=5.21kΩ 30 25 RFREQ=10kΩ 20 15 10 0 0 5 10 15 20 25 30 0 5 10 RFREQ (kΩ) 355 95 IOUT PK-PK (mA) 100 350 345 4.6 4.8 5 25 30 5.2 5.4 90 85 80 4.4 5.6 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 400 FREQUENCY (MHz) 21 20 19 18 17 4.4 20 FIGURE 8. SUPPLY CURRENT vs RAMP 360 340 4.4 15 RAMP (kΩ) FIGURE 7. SUPPLY CURRENT vs RFREQ FREQUENCY (MHz) RFREQ=30kΩ 5 RAMP=20kΩ 0 SUPPLY CURRENT (mA) RFREQ=20kΩ 380 360 340 320 4.6 4.8 5 5.2 5.4 5.6 SUPPLY VOLTAGE (V) FIGURE 11. SUPPLY CURRENT vs SUPPLY VOLTAGE 5 300 -50 0 50 100 150 AMBIENT TEMPERATURE (°C) FIGURE 12. FREQUENCY vs TEMPERATURE EL6208 Typical Performance Curves (Continued) VDD = 5V, TA = 25°C, RL = 10Ω, RFREQ = 5.21kΩ, RAMP = 2.54kΩ, VOUT = 2.2V unless otherwise specified. 95 30 SUPPLY CURRENT (mA) IOUT PK-PK (mA) 90 85 80 75 70 65 60 -50 0 50 100 25 20 15 10 -50 150 0 AMBIENT TEMPERATURE (°C) FIGURE 13. PEAK-TO-PEAK OUTPUT CURRENT vs TEMPERATURE 40mA 50 100 150 AMBIENT TEMPERATURE (°C) FIGURE 14. SUPPLY CURRENT vs TEMPERATURE 40mA 5ns 1ns RFREQ=5.21kΩ RAMP=2.54kΩ RFREQ=30.3kΩ RAMP=2.54kΩ FIGURE 15. OUTPUT CURRENT @60MHz FIGURE 16. OUTPUT CURRENT @350MHz 10 0.5ns RELATIVE AMPLITUDE (dB) 40mA RFREQ=3.03kΩ RAMP=2.54kΩ -10 -30 -50 -70 -90 340 344 348 352 356 360 FREQUENCY (MHz) FIGURE 17. OUTPUT CURRENT @600MHz 6 FIGURE 18. OUTPUT SPECTRUM - WIDEBAND EL6208 Block Diagram VDD 1 OSCILLATOR DRIVER 6 IOUT1 RFREQ 2 RAMP 3 AUTO SHUTOFF 5 GND DRIVER 4 IOUT1 Typical Application Diagram EMI REDUCTION FILTERS TWIN ROM LASER DRIVER IAPC2 GAIN SETTING RESISTORS FREQUENCY SETTING RESISTOR BEAD PNP BEAD LASER DIODE +5V 1 VDD IOUT2 6 RFREQ 2 RFREQ 4.7µF LASER POWER CONTROL 0.1µF 0.1µF GND 5 RAMP LASER DIODE 3 RAMP IOUT1 4 AMPLITUDE SETTING RESISTOR GND MAIN BOARD 0.1µF PHOTO DIODE FLEX ON PICKUP Typical Waveforms ~10mW LASER OUTPUT POWER THRESHOLD CURRENT LASER OUTPUT POWER IAPC 0mW 0mA ~60mA LASER CURRENT OSCILLATOR CURRENT 7 BEAD PNP 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. 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 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 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 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. TJMAX = Maximum junction temperature θJA = Thermal resistance of the package +5V 0.1µF CHIP PDMAX = Maximum power dissipation in the package TAMAX = Maximum ambient temperature L SERIES: 70Ω REACTANCE AT 300MHz VS where: 0.1µF CHIP GND EL6208 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. 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 × 1kΩ 30mA × 1kΩ I SUP = ------------------------------------------- + ---------------------------------- + 0.6mA R FREQ R AMP The power dissipation can be calculated from the following equation: P D = V SUP × I SUP RFREQ SUPPLY BYPASS GND SOURCING CURRENT LOOP 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. Power Dissipation With the high output drive capability, the EL6208 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. The maximum power dissipation allowed in a package is determined according to: T JMAX - T AMAX P DMAX = --------------------------------------------Θ JA 9 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 θJA, and lower power dissipation would then be required. JEDEC JESD51-3 LOW EFFECTIVE THERMAL CONDUCTIVITY TEST BOARD 0.6 POWER DISSIPATION (W) RAMP 488mW 0.5 0.4 θ 6- JA 0.3 Pi n SO =2 T23 56 C/ W 0.2 0.1 0 0 25 50 75 85 100 125 150 AMBIENT TEMPERATURE (°C) FIGURE 22. PACKAGE POWER DISSIPATION vs AMBIENT TEMPERATURE EL6208 JEDEC JESD51-7 HIGH EFFECTIVE THERMAL CONDUCTIVITY TEST BOARD POWER DISSIPATION (W) 0.6 0.5 543mW θ 6- JA 0.4 0.3 Pi n SO =2 T30 23 C/ W 0.2 0.1 0 0 25 50 75 85 100 125 150 AMBIENT TEMPERATURE (°C) FIGURE 23. PACKAGE POWER DISSIPATION vs AMBIENT TEMPERATURE All Intersil U.S. products are manufactured, assembled and tested utilizing ISO9000 quality systems. Intersil Corporation’s quality certifications can be viewed at www.intersil.com/design/quality 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. For information regarding Intersil Corporation and its products, see www.intersil.com 10