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EL6206
Data Sheet June 10, 2004 FN7340
Laser Driver Oscillator
The EL6206 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. One external resistor sets the oscillator frequency. Another external resistor sets the oscillator amplitude. 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 bias 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. This part is pin-compatible to the EL6201. It is superior to the EL6201 in several ways: It has up to 100mA output capability, it is faster (up to 600MHz), it is more powerefficient, it has less harmonic content, and it has an auto shut-off feature activated at 1.1V. The part is available in the space-saving 5-pin SOT23 package. It is specified for operation from 0C to +85C.
Features
* Low power dissipation * User-selectable frequency from 100MHz to 600MHz controlled with a single resistor * User-specified amplitude from 10mAPK-PK to 100mAPK controlled with a single resistor * Auto turn-off threshold * Soft edges for reduced EMI * Small 5-pin SOT23 package
Applications
* DVD players * DVD-ROM drives * CD-RW drives * MO drives * General purpose laser noise reduction
Ordering Information
PART NUMBER EL6206CW-T7 EL6206CW-T7A PACKAGE 5-Pin SOT23 5-Pin SOT23 TAPE & REEL PKG. DWG. # 7" (3K pcs) 7" (250 pcs) MDP0038 MDP0038
Pinout
EL6206 (5-PIN SOT23) TOP VIEW
1 VDD RFREQ 5
2
GND
3
IOUT
RAMP
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 (c) 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.
EL6206
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 +85C Maximum Junction Temperature . . . . . . . . . . . . . . . . . . . . . . +150C Storage Temperature Range . . . . . . . . . . . . . . . . . .-65C to +150C 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 = 25C, RL = 10, RFREQ = 3.5k (FOSC = 550MHz), RAMP = 2540
(IOUT = 50mAP-P measured at 100MHz), VOUT = 2.2V PARAMETER PSOR ISO ISTYP ISLO VFREQ VRAMP VCUTOFF DESCRIPTION Power Supply Operating Range Supply Current Disabled Supply Current Typical Conditions Supply Current Low Conditions Voltage at RFREQ Pin Voltage on RAMP Pin Monitoring Voltage of IOUT Pin 1.1 VOUT < VCUTOFF RFREQ = 3.5k, RAMP = 2.54k RFREQ = 18.2k, RAMP = 12.7k CONDITIONS MIN 4.5 550 22 6 1.27 1.27 1.4 TYP MAX 5.5 750 TBD UNIT V A mA mA V V V
Oscillator Characteristics
PARAMETER FOSC FLOW TCOSC PSRROSC
VDD = +5V, TA = 25C, RL = 10, RFREQ = 3.5k (FOSC = 550MHz), RAMP = 2540 (IOUT = 50mAP-P measured at 100MHz), VOUT = 2.2V CONDITIONS Unit-unit frequency variation RFREQ = 18.2k -40C to +85C ambient VDD from 4.5V to 5.5V MIN TBD TYP 550 100 50 1 MAX TBD UNIT MHz MHz ppm/C %
DESCRIPTION Frequency Tolerance Frequency Range Low Frequency Temperature Sensitivity Frequency Change F/F
Driver Characteristics
PARAMETER AMPHIGH AMPLOW IOSNOM IOSHIGH IOSLOW IOUTP-P Duty Cycle PSRRAMP TON TOFF IOUTN
VDD = +5V, TA = 25C, RL = 10, RFREQ = 18.2k (FOSC = 100MHz), RAMP = 2540 (IOUT = 50mAP-P measured at 100MHz), VOUT = 2.2V CONDITIONS RAMP = 1.27k RAMP = 12.7k RFREQ = 3.5k, VOUT = 2.2V RFREQ = 3.5k, VOUT = 2.8V RFREQ = 3.5k, VOUT = 1.8V Defined as one standard deviation RFREQ = 3.5k VDD from 4.5V to 5.5V Output voltage step from 0V to 2.2V Output voltage step from 2.2V to 0V RFREQ = 5210, measured @ 10MHz MIN TYP 100 10 TBD TBD TBD 2 43 -54 15 0.5 2.5 MAX UNIT mAP-P mAP-P mA mA mA % % dB s s nA/Hz
DESCRIPTION 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 Auto Turn-on Time Auto Turn-off Time Output Current Noise Density
2
EL6206 Pin Descriptions
PIN NAME 1 2 3 4 5 PIN TYPE VDD GND IOUT RAMP RFREQ PIN DESCRIPTION Positive power for laser driver (4.5V - 5.5V) Chip ground pin (0V) Current output to laser diode Set pin for output current amplitude Set pin for oscillator frequency
Recommended Operating Conditions
VDD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5V 10% VOUT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2V - 3V RFREQ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3k (min) RAMP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.25k (min) FOSC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .100-600MHz IOUT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-100mAPK-PK
IOUT Control
VOUT Less than VCUTOFF More than VCUTOFF IOUT OFF Normal Operation
Typical Performance Curves
VDD = 5V, TA = 25C, RL = 10, RFREQ = 3.5k, RAMP = 2.54k, VOUT = 2.2V unless otherwise specified.
FREQUENCY vs RFREQ 700 Frequency=1824 * 1k / RFREQ (MHz) 600 500 400 300 200 100 0 0 5 10 15 20 25 30 35 600 500 400 300 200 100 0 700
FREQUENCY vs 1 / RFREQ
Frequency=1824 * 1k / RFREQ (MHz)
FREQUENCY (MHz)
FREQUENCY (MHz)
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
RFREQ (k)
1k / RFREQ
Block Diagram
VDD
1
DRIVER
OSCILLATOR
5
RFREQ
GND
2
IOUT
3
AUTO SHUT-OFF
REFERENCE AND BIAS
4
RAMP
3
EL6206 Typical Application Circuit
TYPICAL ROM LASER DRIVER GAIN SETTING RESISTOR EMI REDUCTION SUPPLY FILTER
+5V
BEAD
4.7F
0.1F
PNP
1
VDD1
RFREQ
5
2 IAPC CONTROLLER GND BEAD 3 0.1F
GND
RFREQ
IOUT
RAMP
4 RAMP
Laser Diode
EMI REDUCTION FILTER
PHOTO DIODE
AMPLITUDE SETTING RESISTOR
FREQUENCY SETTING RESISTOR
MAIN BOARD
FLEX
ON PICKUP
~10mW
LASER OUTPUT POWER LASER OUTPUT POWER THRESHOLD CURRENT
IAPC 0mW 0mA ~60mA LASER CURRENT
OSCILLATOR CURRENT
4
EL6206 Applications Information
Product Description
The EL6206 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 EL6206 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 EL6206 has the operating frequency from 100MHz to 600MHz and the output current from 10mAP-P to 100mAP-P. The supply current is only 22mA for the output current of 50mAP-P at the operating frequency of 550MHz. 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 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 EL6206'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
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 EL6206's local environment from propagating to the modulation source, and it will keep parasitic capacitance at the pin minimized.
5
EL6206
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.
L Series: 70 reactance at 300MHz VS EL6206 GND 0.1F Chip +5V 0.1F Chip
The maximum power dissipation allowed in a package is determined according to:
T JMAX - T AMAX P DMAX = ------------------------------------------- JA
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 EL6206 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:
------------------------------------------ 30mA x 1k I SUP = 31.25mA x 1k + --------------------------------- + 0.6mA R AMP R FREQ
FIGURE 2. RECOMMENDED SUPPLY BYPASSING
Also important is circuit-board layout. At the EL6206'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 RAMP
The power dissipation can be calculated from the following equation:
P D = V SUP x I SUP
SUPPLY BYPASS
SOURCING CURRENT LOOP
GND
SINKING CURRENT LOOP
LASER DIODE
FIGURE 3. OUTPUT CURRENT LOOPS
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 JA, and lower power dissipation would then be required.
JEDEC JESD51-3 LOW EFFECTIVE THERMAL CONDUCTIVITY TEST BOARD
0.6
For the pushing current loop, the current flows through the bypass capacitor, into the EL6206 supply pin, out the IOUT pin to the laser, and from the laser back to the decoupling capacitor. This loop should be small.
POWER DISSIPATION (W)
0.5
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.
488mW 0.4
5Pi n 25
JA =
0.3
SO T2 3 6 C/ W
Power Dissipation
With the high output drive capability, the EL6206 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.
0.2
0.1
0 0 25 50 75 85 100 125 150
AMBIENT TEMPERATURE (C)
FIGURE 4. PACKAGE POWER DISSIPATION VS AMBIENT TEMPERATURE
6
EL6206
JEDEC JESD51-7 HIGH EFFECTIVE THERMAL CONDUCTIVITY TEST BOARD
0.6
0.5 POWER DISSIPATION (W)
543mW
5Pi n
JA =
0.4
SO T2 23 3 0 C/ W
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
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