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EL6205
Data Sheet March 1, 2004 FN7220.1
Laser Driver Oscillator
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. 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. 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 0C to +70C.
Features
* Low power dissipation * Reduced parts count from the conventional solution * User-selectable frequency from 60MHz to 600MHz controlled with a single resistor * User-selectable amplitude from 15mAPK-PK to 100mAPK-PK controlled by 0.3mA to 2mA input current * 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
Pinout
EL6205 (6-PIN SOT-23) TOP VIEW
Ordering Information
PART NUMBER EL6205CW-T7 EL6205CW-T7A PACKAGE 6-Pin SOT-23 6-Pin SOT-23 TAPE & REEL PKG. DWG. # 7" (3K pcs) 7" (250 pcs) MDP0038 MDP0038
1
IOUT
RFREQ
6
2
VDD
GND2
5
3
GND1
IN
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.
EL6205
Absolute Maximum Ratings (TA = 25C)
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 . . . . . . . . . . . . . . . . . 0C to +70C Maximum Die Operating 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 = 5210 (FOSC = 350MHz), IIN = 1mA
(IOUT = 50mAP-P measured at 60MHz), VOUT = 2.2V PARAMETER PSOR ISO ISTYP ISLO ISHI VFREQ RIN DESCRIPTION Power Supply Operating Range Supply Current Disabled Supply Current Typical Conditions Supply Current Low Conditions Supply Current High Conditions Voltage at RFREQ Pin Input Impedance IIN 100A RFREQ = 5.21k (includes laser current) RFREQ = 30.5k, IIN = 300A (includes laser current) RFREQ = 3.05k, IIN = 2mA (includes laser current) 25 CONDITIONS MIN 4.5 550 32 10 53 1.27 500 TYP MAX 5.5 750 38 UNIT V A mA mA mA V
Oscillator Characteristics
PARAMETER FOSC FHIGH FLOW TCOSC PSRROSC
VDD = +5V, TA = 25C, RL = 10, RFREQ = 5210 (FOSC = 350MHz), IIN = 1mA (IOUT = 50mAP-P measured at 60MHz), VOUT = 2.2V CONDITIONS Unit-unit frequency variation RFREQ = 3.05k RFREQ = 30.5k 0C to 70C ambient VDD from 4.5V to 5.5V MIN 300 TYP 350 600 60 50 1 MAX 400 UNIT MHz MHz MHz ppm/C %
DESCRIPTION Frequency Tolerance Frequency Range High Frequency Range Low Frequency Temperature Sensitivity Frequency Change F/F
Driver Characteristics
PARAMETER AMPHIGH AMPLOW IAVG IOUTP-P Duty Cycle PSRRAMP TON TOFF INOUT
VDD = +5V, TA = 25C, RL = 10, RFREQ = 30.5k (FOSC = 60MHz), IIN = 1mA (IOUT = 50mAP-P measured at 60MHz), VOUT = 2.2V DESCRIPTION CONDITIONS IIN = 2mA IIN = 300A RFREQ = 5210 Defined as one standard deviation RFREQ = 5210 VDD from 4.5V to 5.5V Input current step from 0mA to 1mA Input current step from 1mA to 0mA MIN TYP 100 15 20 2 43 -54 15 0.5 2.5 MAX UNIT mAP-P mAP-P mA % % dB us us nA/Hz
Amplitude Range High Amplitude Range Low Average Output Current @ 2.2V Output Current Tolerance Output Push Time/Cycle Time Amplitude Change of Output I/I Auto Turn-on Time Auto Turn-off Time
IOUT Current Output Noise Density RFREQ = 5490, FMEASURE = 10MHz
2
EL6205 Control Table
IIN 100A 300A IOUT OFF Normal Operation
Pin Descriptions
PIN NUMBER 1 2 3 4 5 6 PIN NAME IOUT VDD GND1 IN GND2 RFREQ Current output to laser diode Positive power for chip and laser driver (4.5V - 5.5V) Chip ground pin Set pin for output current amplitude Chip ground pin (0V for RFREQ) Set pin for oscillator frequency PIN DESCRIPTION
Recommended Operating Conditions
VDD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5V 10% VOUT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2V-3V RFREQ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3k (min) IIN. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2mA (max) FOSC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .60-600MHz IOUT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15-100mAPK-PK
Typical Performance Curves
VDD = 5V, TA = 25C, RL = 10, RFREQ = 5.21k, IIN = 1mA, VOUT = 2.2V unless otherwise specified.
Frequency Distribution 500 Typical Production Distortion 8 7 6 Number of Parts Number of Parts 300 5 4 3 2 100 1 0 310 318 326 334 342 350 358 366 374 382 390 0 6 18 30 42 54 66 78 90 Measured from -40C to +85C Frequency Drift with Temperature
400
200
Frequency (MHz)
Frequency TC (ppm/C)
3
EL6205 Typical Performance Curves
Frequency vs RFREQ 700 Frequency=1824 * 1k / RFREQ (MHz) 600 500 Frequency (MHz) 400 300 200 100 0 0 5 10 15 20 25 30 35 Frequency (MHz) 600 500 400 300 200 100 0 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 700 Frequency=1824 * 1k / RFREQ (MHz)
(Continued) VDD = 5V, TA = 25C, RL = 10, RFREQ = 5.21k, IIN = 1mA, VOUT = 2.2V unless otherwise specified.
Frequency vs 1 / RFREQ
RFREQ (k)
1k / RFREQ
Amplitude vs IIN 100 Amplitude = 50 * IIN 80 Amplitude (mAPK-PK) 355 60 Frequency (MHz) 360
Frequency vs Supply Voltage
350
40
345 20
0 0 1 IIN (mA) 2
340 4.4
4.6
4.8
5
5.2
5.4
5.6
Supply Voltage (V)
Frequency vs Temperature 400
380 Frequency (MHz)
360
340
320
300 -50
0
50 Ambient Temperature (C)
100
150
4
EL6205 Block Diagram
IOUT 1 DRIVER OSCILLATOR 6 RFREQ
VDD
2
5
GND2
GND1
3
BANDGAP REFERENCE
AUTO SHUT-OFF
4
IN
Typical Application Circuit
Typical ROM Laser Driver Gain Setting Resistor EMI Reduction Filters Frequency Setting Resistor
PNP RFREQ 1 BEAD Laser Diode 0.1F GND optional RF Blocking Resistor Loop Compensation & Noise Reduction Capacitor 0.1F 2 VDD GND2 5 IOUT RFREQ 6
+5V Controller
3 4.7F
GND1
IN
4
Photo Diode
Main Board
Flex
On Pickup
~10mW
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 100A. 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. 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 -
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.
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: 70 reactance at 300MHz (see text) VS EL6205 GND 0.1F Chip +5V 0.1F Chip
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
FIGURE 2. RECOMMENDED SUPPLY BYPASSING
6
EL6205
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.
RFREQ RAMP Supply Bypass Sourcing Current Loop
The power dissipation can be calculated from the following equation:
P D = V SUP x I SUP1 + ( V SUP - V LAS ) x I SUP2
LOAD GND (8-Pin Package)
FIGURE 3. OUTPUT CURRENT LOOP
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 JA 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) 0.45 0.4 435mW 0.35 0.3 0.25 0.2 0.15 0.1 0.05 0 0 25 50 75 85 100 125 150 SOT23-5/6 JA=230C/W JEDEC JESD51-7 HIGH EFFECTIVE THERMAL CONDUCTIVITY TEST BOARD
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.
AMBIENT TEMPERATURE (C) JEDEC JESD51-3 LOW EFFECTIVE THERMAL CONDUCTIVITY TEST BOARD 391mW
SO =2
Power Dissipation
POWER DISSIPATION (W)
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 = ------------------------------------------- JA
0.45 0.4 0.35 0.3 0.25 0.2 0.15 0.1 0.05 0
JA
T2 3 56 -5-6 C /W
0
25
50
75 85 100
125
150
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 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 x 1k I SUP1 = ---------------------------------- + 0.5mA R FREQ I SUP2 = 50 x I IN x 0.5
AMBIENT TEMPERATURE (C)
FIGURE 4. PACKAGE POWER DISSIPATION vs AMBIENT TEMPERATURE
7
EL6205
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