EL6205 ® Data Sheet March 1, 2004 FN7220.1 Laser Driver Oscillator Features The EL6205 consists of a variable amplitude, push only, oscillator that also supplies the laser DC current. It is designed to easily interface to existing ROM controllers, reducing parts count, and power dissipation. • Low power dissipation The reduction of parts count and the small package allows the oscillator to be placed closer to the laser, thus reducing EMI. Also, the turn-on and turn-off edges are slew rate limited to reduce higher harmonics. • User-selectable amplitude from 15mAPK-PK to 100mAPK-PK controlled by 0.3mA to 2mA input current The total current drawn from the power supply can be less than the laser threshold current due to the unique push-only modulation method. The average current is less than the peak oscillator current, and can be less than half of the oscillator current. The power control current supplied from the main board is reduced to less than 2mA. One external resistor sets the oscillator frequency. A current applied to the IIN terminal determines the amplitude of the oscillator and laser DC current. If the oscillator amplitude is set very low, the output and oscillator are disabled. The part is available in the space-saving 6-pin SOT-23 package. It is specified for operation from 0°C to +70°C. • Reduced parts count from the conventional solution • User-selectable frequency from 60MHz to 600MHz 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 • Combo drives • MO drives • General purpose laser noise reduction • Local oscillator capability Ordering Information Pinout PART NUMBER EL6205 (6-PIN SOT-23) TOP VIEW 1 IOUT RFREQ 6 2 VDD GND2 5 3 GND1 IN 4 1 PACKAGE TAPE & REEL PKG. DWG. # EL6205CW-T7 6-Pin SOT-23 7” (3K pcs) MDP0038 EL6205CW-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. EL6205 Absolute Maximum Ratings (TA = 25°C) Voltages Applied to: VDD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.5V to +6.0V IOUT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.5V to +6.0V RFREQ, IN . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.5V to +6.0V Operating Ambient Temperature . . . . . . . . . . . . . . . . . 0°C to +70°C Maximum Die Operating 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), IIN = 1mA (IOUT = 50mAP-P measured at 60MHz), VOUT = 2.2V PARAMETER DESCRIPTION CONDITIONS MIN TYP MAX UNIT 5.5 V 550 750 µA 32 38 mA PSOR Power Supply Operating Range ISO Supply Current Disabled IIN ≤ 100µA ISTYP Supply Current Typical Conditions RFREQ = 5.21kΩ (includes laser current) ISLO Supply Current Low Conditions RFREQ = 30.5kΩ, IIN = 300µA (includes laser current) 10 mA ISHI Supply Current High Conditions RFREQ = 3.05kΩ, IIN = 2mA (includes laser current) 53 mA VFREQ Voltage at RFREQ Pin 1.27 V RIN Input Impedance 500 Ω Oscillator Characteristics 4.5 25 VDD = +5V, TA = 25°C, RL = 10Ω, RFREQ = 5210Ω (FOSC = 350MHz), IIN = 1mA (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), IIN = 1mA (IOUT = 50mAP-P measured at 60MHz), VOUT = 2.2V PARAMETER DESCRIPTION CONDITIONS MIN TYP MAX UNIT AMPHIGH Amplitude Range High IIN = 2mA 100 mAP-P AMPLOW Amplitude Range Low IIN = 300µA 15 mAP-P IAVG Average Output Current @ 2.2V RFREQ = 5210Ω 20 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 Input current step from 0mA to 1mA 15 us TOFF Auto Turn-off Time Input current step from 1mA to 0mA 0.5 us INOUT IOUT Current Output Noise Density RFREQ = 5490Ω, FMEASURE = 10MHz 2.5 nA/√Hz 2 EL6205 Control Table IIN IOUT ≤ 100µA OFF ≥ 300µA Normal Operation Pin Descriptions PIN NUMBER PIN NAME PIN DESCRIPTION 1 IOUT Current output to laser diode 2 VDD Positive power for chip and laser driver (4.5V - 5.5V) 3 GND1 4 IN 5 GND2 6 RFREQ Chip ground pin Set pin for output current amplitude Chip ground pin (0V for RFREQ) Set pin for oscillator frequency Recommended Operating Conditions IIN. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2mA (max) FOSC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .60-600MHz IOUT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-100mAPK-PK VDD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5V ±10% VOUT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2V-3V RFREQ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3kΩ (min) Typical Performance Curves VDD = 5V, TA = 25°C, RL = 10Ω, RFREQ = 5.21kΩ, IIN = 1mA, VOUT = 2.2V unless otherwise specified. Frequency Distribution Frequency Drift with Temperature 500 400 8 Typical Production Distortion 7 Measured from -40°C to +85°C Number of Parts 300 200 5 4 3 2 100 1 Frequency (MHz) 3 Frequency TC (ppm/°C) 90 78 66 54 42 30 18 6 390 382 374 366 358 350 342 334 326 0 318 0 310 Number of Parts 6 EL6205 Typical Performance Curves (Continued) VDD = 5V, TA = 25°C, RL = 10Ω, RFREQ = 5.21kΩ, IIN = 1mA, VOUT = 2.2V unless otherwise specified. Frequency vs RFREQ Frequency vs 1 / RFREQ 700 700 Frequency=1824 * 1kΩ / RFREQ (MHz) 600 600 500 500 Frequency (MHz) Frequency (MHz) Frequency=1824 * 1kΩ / RFREQ (MHz) 400 300 400 300 200 200 100 100 0 0 0 5 10 15 20 25 30 35 0 0.05 0.1 0.15 RFREQ (kΩ) 0.2 0.25 0.3 0.35 1kΩ / RFREQ Amplitude vs IIN Frequency vs Supply Voltage 360 100 Amplitude = 50 * IIN Frequency (MHz) 355 60 40 350 345 20 0 0 1 340 4.4 2 4.6 4.8 Frequency vs Temperature 400 380 360 340 320 300 -50 0 50 Ambient Temperature (°C) 4 5 5.2 Supply Voltage (V) IIN (mA) Frequency (MHz) Amplitude (mAPK-PK) 80 100 150 5.4 5.6 EL6205 Block Diagram IOUT 1 VDD 2 GND1 3 DRIVER OSCILLATOR BANDGAP REFERENCE AUTO SHUT-OFF 6 RFREQ 5 GND2 4 IN Typical Application Circuit Typical ROM Laser Driver Gain Setting Resistor EMI Reduction Filters Frequency Setting Resistor PNP RFREQ 1 IOUT RFREQ 6 2 VDD GND2 5 3 GND1 IN 4 BEAD Laser Diode +5V Controller 4.7µF 0.1µF 0.1µF GND optional RF Blocking Resistor Main Board Flex ~10mW Loop Compensation & Noise Reduction Capacitor Photo Diode On Pickup Laser Output Power Laser Output Power Threshold Current 0mW 0mA ~60mA Laser Current Oscillator Current 5 EL6205 Applications Information Product Description The EL6205 is a solid state, low-power, high-speed laser modulation oscillator with external resistor-adjustable operating frequency. 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 EL6205 is composed of a push current source switched at the oscillator frequency. The output and oscillator are automatically disabled for power saving when the average input current drops to less than 100µA. The EL6205 has the operating frequency from 60-600MHz and the output current from 10mAP-P to 100mAP-P. The supply current is only 30mA (includes laser current) 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 provided to the laser diode. The 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 pushing-current time. The signal-tonoise 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 no output current time, the noise is also very low. oscillator takes on the role of supplying the total laser current. The IIN current is the previous read current (reduced in amplitude). Thus it does not need to be set, since it is within the control loop. The current capability of the external source for IIN should be made large enough to power the worst, hottest old laser. RFREQ Pin Interfacing Figure 1 shows an equivalent circuit of pins associated with the RFREQ resistor. VREF is roughly 1.27V. The resistor RFREQ should be connected to the non-load side of the power ground to avoid noise. This resistor should also return to the EL6202’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. RFREQ PIN INTERFACE External voltage sources can be coupled to the RFREQ pin to effect frequency 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 high-frequency noise of the EL6205'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 noise on the power lines is common. There needs to be a lossy series bead inductance and secondary bypass on the supply side to control signals from propagating down the wires. Figure 2 shows the typical connection. L Series: 70Ω reactance at 300MHz (see text) VS EL6205 +5V 0.1µF Chip 0.1µF Chip GND Setting the IIN Current By looking the typical application circuit, it can be seen that the push only oscillator is more efficient at the laser than the conventional push-pull oscillator. The significant current from the main board is reduced to be IIN (≤2mA), while the 6 FIGURE 2. RECOMMENDED SUPPLY BYPASSING EL6205 RFREQ Supply Bypass RAMP Sourcing Current Loop LOAD GND (8-Pin Package) FIGURE 3. OUTPUT CURRENT LOOP For the current loop, the current flows through the supply bypass-capacitor. The ground end of the bypass thus should be connected directly to the EL6205 ground pin and laser ground. A long ground return path will cause the bypass capacitor currents to generate voltage drops in the ground plane of the circuit board, and other components (such as RFREQ) will pick this up as an interfering signal. Similarly, the ground return of the load should be considered, as noisy and other grounded components should not connect to this path. Slotting the ground plane around the load's return will reduce adjacent grounded components from seeing the noise. The power dissipation can be calculated from the following equation: P D = V SUP × I SUP1 + ( V SUP - V LAS ) × I SUP2 Here, VSUP is the supply voltage and VLAS is the average voltage of the laser diode. Figure 4 provides a convenient way to see if the device may overheat. The maximum safe power dissipation can be found graphically, based on the ambient temperature and JEDEC standard single layer PCB. For flex circuits, the θJA could be higher. By using the previous equation, it is possible to estimate if PD exceeds the device's power derating curve. To ensure proper operation, it is important to observe the recommended derating curve shown in Figure 4. 0.5 POWER DISSIPATION (W) Also important is circuit-board layout. At the EL6205'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 loop. 0.45 0.4 435mW 0.35 SOT23-5/6 0.3 θJA=230°C/W 0.25 0.2 0.15 0.1 0.05 0 T JMAX - T AMAX P DMAX = -------------------------------------------Θ JA where: 0.45 POWER DISSIPATION (W) The maximum power dissipation allowed in a package is determined according to: 0 25 50 75 85 100 125 150 AMBIENT TEMPERATURE (°C) Power Dissipation 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. JEDEC JESD51-7 HIGH EFFECTIVE THERMAL CONDUCTIVITY TEST BOARD JEDEC JESD51-3 LOW EFFECTIVE THERMAL CONDUCTIVITY TEST BOARD 391mW 0.4 0.35 θ 0.3 JA 0.25 0.2 SO =2 T2 3 56 -5-6 °C /W 0.15 0.1 0.05 0 0 25 50 75 85 100 125 150 AMBIENT TEMPERATURE (°C) PDMAX = Maximum power dissipation in the package TJMAX = Maximum junction temperature TAMAX = Maximum ambient temperature θJA = Thermal resistance of the package The supply current of the EL6205 depends on the peak-topeak output current and the operating frequency which are determined by resistor RFREQ. The supply current can be predicted approximately by the following equations: 35mA × 1kΩ I SUP1 = ---------------------------------- + 0.5mA R FREQ I SUP2 = 50 × I IN × 0.5 7 FIGURE 4. PACKAGE POWER DISSIPATION vs AMBIENT TEMPERATURE EL6205 All Intersil U.S. products are manufactured, assembled and tested utilizing ISO9000 quality systems. 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