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 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. 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