EL6207 ® Data Sheet October 10, 2002 Dual Laser Driver Oscillator Features The EL6207 is a dual push-pull oscillator used to reduce laser noise. It is optimized for 350MHz operation, allowing reduced concern for harmonic EMI. It uses the standard interface to existing ROM controllers. The frequency and amplitude are each set with a separate resistor connected to ground, for each output. The tiny package and harmonic reduction allow the part to be placed close to a laser with low RF emissions. • Low power dissipation If the voltage at both IOUT pins is less than 1.0V, the chip will be powered down and not oscillate. If the voltage at either IOUT pin is above 1.4V, the chip will be powered up and oscillating. If both IOUT pins are above 1.4V, the chip will also be powered down, and not oscillate. The current drawn by the oscillator consists of a small utility current, plus the peak oscillator amplitude in the positive cycle, which is routed to the enabled IOUT pin. In the negative cycle the oscillator subtracts peak oscillator amplitude from the laser APC current. FN7221 • User-selectable frequency from 100MHz to 600MHz controlled with a single resistor for each laser • User-specified amplitude from 10mAPK-PK to 100mAPK controlled with a single resistor for each output • Auto turn-off threshold • Soft edges for reduced EMI • Small 8-pin LPP package Applications • Combi drive using dual laser Ordering Information PART NUMBER EL6207CL PACKAGE TAPE & REEL PKG. NO. 8-Pin LPP - MDP0047 The part operates from a single 5V supply, and is specified for operation from 0°C to +85°C. Pinout EL6207 (8-PIN LPP) TOP VIEW VDD 1 8 RAMP1 IOUT1 2 7 RAMP2 6 RFREQ1 GND 3 5 RFREQ IOUT2 4 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. EL6207 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 Die Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . +150°C Storage Temperature Range . . . . . . . . . . . . . . . . . .-65°C to +150°C IOUT Current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100mAPK-PK Power Dissipation (maximum) . . . . . . . . . . . . . . . . . . . . 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 (FREQ = 360MHz), RAMP = 2540Ω (Amp = 50mAP-P measured at 95MHz), VOUT = 2.2V (One channel active) PARAMETER DESCRIPTION CONDITIONS MIN TYP UNIT 5.5 V PSOR Power Supply Operating Range ISO Supply Current Disabled VOUT1 and VOUT2 < 1.3V 550 750 µA ISTYP Supply Current Typical Conditions RFREQ = 5.21kΩ, RAMP = 2.54kΩ, VOUT1 or VOUT2 >1.4V 17 22 mA ISLO Supply Current Low Conditions RFREQ = 18.2kΩ, RAMP = 13kΩ, VOUT1 or VOUT2 >1.4V 6 mA ISHI Supply Current High Conditions RFREQ = 3.05kΩ, RAMP = 1.3kΩ, VOUT1 or VOUT2 >1.4 32 mA VCUTOFF Output Cutoff Voltage Average voltage at cutoff VFREQ Voltage at RFREQ Pin 1.27 V VRAMP Voltage on RAMP Pin 1.27 V Oscillator Characteristics 4.5 MAX 1.1 1.4 V VDD = +5V, TA = 25°C, RL = 10Ω, RFREQ = 5210Ω (FREQ = 360MHz), RAMP = 2540Ω (Amp = 50mAP-P measured at 100MHz), VOUT = 2.2V (One channel active) PARAMETER DESCRIPTION CONDITIONS MIN TYP MAX UNIT 310 360 410 MHz FOSC Frequency Tolerance Unit-unit frequency variation FHIGH Frequency Range High RFREQ = 3.0kΩ 600 MHz 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 1 % Driver Characteristics VDD from 4.5V to 5.5V VDD = +5V, TA = 25°C, RL = 10Ω, RFREQ = 18.2kΩ (FREQ = 100MHz), RAMP = 2540Ω (Amp = 50mAP-P measured at 100MHz), VOUT = 2.2V (One channel active) 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 IOFFNOM Average Output Current @ 2.2V RFREQ = 5210Ω, 10Ω load, VOUT = 2.2V -4 mA IOFFHIGH Average Output Current @ 2.8V RFREQ = 5210Ω, 10Ω load, VOUT = 3.0V -4.8 mA IOFFLOW Average Output Current @ 1.8V RFREQ = 5210Ω, 10Ω load, VOUT = 1.8V -3.5 mA IOUTP-P Output Current Tolerance Defined as on 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 EL6207 Driver Characteristics VDD = +5V, TA = 25°C, RL = 10Ω, RFREQ = 18.2kΩ (FREQ = 100MHz), RAMP = 2540Ω (Amp = 50mAP-P measured at 100MHz), VOUT = 2.2V (One channel active) (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 INOUT IOUT Current Output Noise Density RFREQ = 5210Ω, FMEASURE = 10MHz 2.5 nA/√Hz Pin Descriptions PIN NAME PIN TYPE PIN DESCRIPTION 1 VDD 2 IOUT1 3 GND 4 IOUT1 Current output to laser anode 5 RFREQ2 Set pin for oscillator frequency 6 RFREQ1 Set pin for oscillator frequency 7 RAMP2 Amplitude control input pin 8 RAMP1 Amplitude control input pin Positive power for laser driver (4.5V - 5.5V) Current output to laser anode Chip ground pin (0V) Recommended Operating Conditions VDD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5V ±10% VOUT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2V - 3V RFREQ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3kΩ (min) RAMP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.3kΩ (min) FOSC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .80-600MHz AOSC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-100mAPK-PK IOUT Control VOUT1 VOUT2 IOUT IOUT Less than VCUTOFF Less than VCUTOFF OFF OFF Less than VCUTOFF More than VCUTOFF OFF Normal Operation More than VCUTOFF Less than VCUTOFF Normal Operation OFF More than VCUTOFF More than VCUTOFF OFF OFF 3 EL6207 Block Diagram Gain Setting Resistor Typical ROM Laser Driver EMI Reduction Supply Filter +5V BEAD 4.7µF EMI Reduction Filters Controller 0.1uF 0.1uF PNP Amplitude Setting Resistors 1 VDD RAMP1 8 2 IOUT1 RAMP2 7 3 GND RFREQ1 6 4 IOUT2 RFREQ2 5 BEAD PNP 0.1uF BEAD 0.1uF Laser GND Rear Photodiode Frequency Setting Resistor Calibration Pots Flex Main Board 4 On Pickup EL6207 Block Diagram VDD IOUT 1 (Continued) BAND GAP REFERENCE 1 3 DRIVER AMPLIFIER AMPLIFIER GND RAMP 1 7 RAMP 2 6 RFREQ 1 5 RFREQ 2 2 OSCILLATOR SELECT ENABLE LOGIC IOUT 2 8 4 DRIVER 5 EL6207 Laser Output Power ~10mW Laser Output Power Threshold Current 0mW 0mA ~60mA Laser Current Oscillator Current External Read Current FIGURE 1. Amplitude vs RAMP Frequency vs RFREQ 600 100 Amplitude = 127x1k / RAMP mAPK-PK Frequency = 1840 x1k/ RFREQ MHz 500 Frequency MHz Amplitude (mA pk-pk) 80 60 40 20 400 300 200 100 0 0 0 4k 8k RAMP Value 6 12k 16k 0 4k 8k 12k RFREQ 16k 20k EL6207 Applications Information 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 forward current will cause rapid increases in laser output power. A typical threshold current is 30mA 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 typically have a noise level above threshold that is almost constant regardless of the power level. The signal-to-noise ratio of the output power can be defined by the DC power level divided by the laser noise power. Because of the almost constant noise power above threshold, higher level of output power have higher SNR (signal-to-noise ratio). Generally it is desirable to make the oscillator current 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 waveshape 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. Also, the amount of junction current causing laser emission is variable with frequency due to the junction capacitance. But even this easy case is not available because the output impedance of the oscillator changes somewhat with output voltage. In conclusion, the size of the RAMP resistor must be determined experimentally. But, a good starting point is to use a peak amplitude that is less than the minimum laser threshold current. The RF oscillator is designed to produce a low noise oscillating current that is added to the external DC current. The effect of the AC current is to cause the laser power to change at twice the oscillator frequency. This changing power level causes the laser to go through rapid mode hopping. The low frequency component of laser power noise due to mode hoping 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 servo 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 on cycle. The SNR is better at higher laser powers. In addition, when the laser is off, the noise is also very low. Setting the RAMP Resistor The laser should always have a forward current during operation. This will prevent the laser voltage from collapsing, and ensure that the high frequency components reach the junction without having to charge the junction capacitance. By looking at Figure 1, it can be seen that the applied DC current should be larger than the peak oscillator current. 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 7