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PDF AD9660 Data sheet ( Hoja de datos )
| Número de pieza | AD9660 | |
| Descripción | 200 MHz Laser Diode Driver with Light Power Control | |
| Fabricantes | Analog Devices | |
| Logotipo |  |
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a
FEATURES
1.5 ns Rise/2.0 ns Fall Times
Output Current: 180 mA @ 3 V, 200 mA @ 2.5 V
Bias Current: 90 mA @ 3 V
Modulation Current: 60 mA @ 3 V
Offset Current: 30 mA @ 3 V
Single +5 V Power Supply
Switching Rate: 200 MHz
Onboard Light Power Control Loops
APPLICATIONS
Laser Printers and Copiers
Optical Disk Drives
FO Datacomm
200 MHz Laser Diode Driver
with Light Power Control
AD9660
FUNCTIONAL BLOCK DIAGRAM
WRITE
PULSE
WRITE
CALIBRATE
WRITE
LEVEL
BIAS
LEVEL
BIAS
CAL
T/H V:1
OUTPUT
DRIVER
TRANSIMPEDANCE
AMPLIFIER
BIAS
T/H
V:1
OUTPUT
DRIVER
AD9660
OUTPUT
SENSE
INPUT
PHOTO
DETECTOR
DIODE
LASER
DIODE
GENERAL DESCRIPTION
The AD9660 is a highly integrated driver for laser diode appli-
cations such as optical disk drives, printers, and copiers. The
AD9660 gets feedback from an external photo detector and in-
cludes two analog feedback loops to allow users to set “bias”
and “write” (for optical disk drives) power levels of the laser,
and switch between the two power levels at up to 200 MHz.
Output rise and fall times are typically 1.5 ns and 2.0 ns to
complement printer applications that use image enhancing tech-
niques such as pulse width modulation to achieve gray scale,
and allow disk drive applications to improve density and take
advantage of pulsed write formats. Control signals are TTL/
CMOS compatible.
The driver output provides up to 180 mA of current @ 3 V,
90 mA of BIAS current, 60 mA of modulation current, and
30 mA of offset current. The onboard disable circuit turns off
the output drivers and returns the light power control loops to a
safe state.
The AD9660 can also be used in closed loop applications in
which the output power level follows an analog WRITE LEVEL
voltage input. By optimizing the external hold capacitor, and
the photo detector, the write loop can achieve bandwidths as
high as 25 MHz.
The AD9660 is offered in a 28-pin plastic SOIC for operation
over the commercial temperature range (0°C to +70°C).
REV. 0
Information furnished by Analog Devices is believed to be accurate and
reliable. However, no responsibility is assumed by Analog Devices 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 Analog Devices.
© Analog Devices, Inc., 1995
One Technology Way, P.O. Box 9106, Norwood. MA 02062-9106, U.S.A.
Tel: 617/329-4700
Fax: 617/326-8703
1 page  
Typical Performance Characteristics–AD9660
6.25mV
–193.8mV
20mV
2ns
ML64116R
OUTPUT
TEK 11802
50Ω O'SCOPE
AD9660
–120V
ANTEL
ARS1
PHOTO DETECTOR
50Ω
Figure 1. Driving ML64116R Laser @ 30 mW
35
30
25
20
15
10
5
0
0 5 10 15 20
ROFFSET – kΩ
Figure 2. IOFFSET vs. ROFFSET
25
THEORY OF OPERATION
The AD9660 combines a very fast output current switch with
onboard analog light power control loops to provide the user
with a complete laser diode driver solution. The block diagram
illustrates the key internal functions. The control loops of the
AD9660, the bias loop and the write loop, adjust the output
current level, IOUT, so that the photo diode feedback current,
IMONITOR, out of SENSE IN is proportional to the analog input
voltage at BIAS LEVEL or WRITE LEVEL. Since the monitor
current is proportional to the laser diode light power, the loops
effectively control laser power to a level proportional to the ana-
log inputs. The control loops should be periodically calibrated
independently (see Choosing CBIAS HOLD and CWRITE HOLD).
The offset current generator produces an open loop output cur-
rent, IOFFSET. Its level is controlled by an external set resistor or
a current out DAC (see Figure 2). While IOFFSET is not cali-
brated as the currents from the bias and write loops are, it can
be very versatile (see Offset Current below).
WRITE HOLD
DISABLE
WRITE PULSE
TTL
TTL
TTL
WRITE CAL
WRITE LEVEL
ANALOG
CGAIN
GAIN
50
RGAIN
POWER
MONITOR
ANALOG
BIAS LEVEL
ANALOG
TTL
BIAS CAL
BIAS HOLD
TTL
OFFSET PULSE
DISABLE
CIRCUIT
AD9660
VOLT
REF
VREFOUT
*
DELAY
5pF V:1
VREF
IMODULATION
1:10
IOUT
OUTPUT
2* IMONITOR
TZA
VREF
1.85:1
4.0V SENSE IN
IMONITOR
VREF
5pF
V:1
IBIAS
1:10
WRITE LOOP
LASER
DIODE
PHOTO
DETECTOR
BIAS LOOP
1:10
IOFFSET
1.4V
Figure 3. Functional Block Diagram
OFFSET CURRENT
SET
+VS
* 10ns DELAY ON RISING
EDGE; 0ns ON FALLING
REV. 0
–5–
5 Page 
AD9660
The trace from the output pins of the AD9660 to the anode of
the laser (send trace) should be several millimeters wide and
should be as direct as possible. The return current will choose
the path of least resistance. If the return path is the ground
plane, it should have an unbroken path, under the output trace,
from the laser cathode back to the AD9660. If the return path is
not the ground plane (such as on a two layer board, or on the
+VS plane), it should still be on the board plane adjacent to the
plane of the output trace. If the current cannot return along a
path that follows the output trace, the inductance will be drasti-
cally increased and performance will be degraded.
Optimizing the Feedback Layout
In applications where the dynamic performance of the analog
feedback loop is important, it is necessary to optimize the layout
of the gain resistor, RGAIN, as well as the monitor current path to
SENSE IN. Such applications include MOD systems which
recalibrate the write loop on pulses as short as 25 ns, and closed
loop applications.
The best possible TZA settling will be achieved by using a
single carbon surface mount resistor (usually 5% tolerance) for
RGAIN and small surface mount capacitor for CGAIN. Because the
GAIN pin (Pin 9) is essentially connected to the inverting input
of the TZA, it is very sensitive to stray capacitance. RGAIN
should be placed between Pin 9 and Pin 10, as close as possible
to Pin 9. Small traces should be used, and the ground and +VS
planes adjacent to the trace should be removed to further mini-
mize stray capacitance.
The trace from SENSE IN to the cathode of the PIN photo-
detector should be thin and routed away from the laser anode
trace.
+VS PIN CONNECTIONS
5
AD9660
OUTPUT PIN CONNECTIONS
PIN ASSIGNMENTS
MUTUAL COUPLING
REDUCES INDUCTANCE
25
24
23
22
21
20
19
4
BYPASS CAPS
GROUND PIN
CONNECTIONS
GROUND PLANE
LASER DIODE CURRENT
PATH SEGMENTS
(SEE TEXT)
1
3
2
Figure 11. Laser Diode Current Loop
REV. 0
–11–
11 Page | ||
| Páginas | Total 12 Páginas | |
| PDF Descargar | [ Datasheet AD9660.PDF ] | |
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