DATASHEET

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.
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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.
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