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PDF AD9661A Data sheet ( Hoja de datos )
| Número de pieza | AD9661A | |
| Descripción | Laser Diode Driver with Light Power Control | |
| Fabricantes | Analog Devices | |
| Logotipo |  |
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a
Laser Diode Driver
with Light Power Control
AD9661A
FEATURES
< 2 ns Rise/Fall Times
Output Current: 120 mA
Single +5 V Power Supply
Switching Rate: 200 MHz typ
Onboard Light Power Control Loop
APPLICATIONS
Laser Printers and Copiers
GENERAL DESCRIPTION
The AD9661A is a highly integrated driver for laser diode appli-
cations such as printers and copiers. The AD9661A gets feed-
back from an external photo detector and includes an analog
feedback loop to allow users to set the power level of the laser,
and switch the laser on and off at up to 100 MHz. Output rise
and fall times are 2 ns to complement printer applications that
use image enhancing techniques such as pulse width modula-
tion to achieve gray scale and resolution enhancement. Control
signals are TTL/CMOS compatible.
The driver output provides up to 120 mA of current into an
infrared N type laser, and the onboard disable circuit turns off
the output driver and returns the light power control loop to a
safe state.
The AD9661A can also be used in closed-loop applications in
which the output power level follows an analog POWER LEVEL
voltage input. By optimizing the external hold capacitor and
the photo detector, the loop can achieve bandwidths as high as
25 MHz.
The AD9661A is offered in a 28-pin plastic SOIC for
operation over the commercial temperature range (0°C to
+70°C).
FUNCTIONAL BLOCK DIAGRAM
TTL
DISABLE
TTL
PULSE
DISABLE
CIRCUIT
*13ns DELAY ON RISING
EDGE; 0ns ON FALLING
PULSE2 TTL
HOLD
CAL TTL
*DELAY
VOLT
REF
VREF
+5V
POWER
LEVEL
ANALOG
VLEVEL SHIFT IN + VREF
LEVEL
SHIFT OUT
LEVEL
8
LEVEL
SHIFT IN
SHIFT
CIRCUIT
DAC
0–1.6V
V1
5pF
REF
3–120mA
1:10
IOUT
LASER
DIODE
OUTPUT
AD9661A
PHOTO
DETECTOR
GAIN
50Ω
CGAIN
RGAIN
POWER
MONITOR
ANALOG
VREF
1:1
IMONITOR
IMONITOR
SENSE IN
1.0V
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  
THEORY OF OPERATION
The AD9661A combines a very fast output current switch with
an onboard analog light power control loop to provide the user
with a complete laser diode driver solution. The block diagram
illustrates the key internal functions. The control loop of the
AD9661A adjusts the output current level, IOUT, so that the
photo diode feedback current, IMONITOR, into SENSE IN is pro-
portional to the analog input voltage at POWER LEVEL. Since
the monitor current is proportional to the laser diode light
power, the loop effectively controls laser power to a level pro-
portional to the analog input. The control loop should be peri-
odically calibrated (see Choosing CHOLD).
The disable circuit turns off IOUT and returns the hold capacitor
voltages to their minimum levels (minimum output current)
when DISABLE = logic HIGH. It is used during initial power
up of the AD9661A or during time periods where the laser is
inactive. When the AD9661A is re-enabled the control loop
must be recalibrated.
Normal operation of the AD9661A involves the following (in
order, see Figure 1):
1. The AD9661A is enabled (DISABLE = logic LOW).
2. The input voltage (POWER LEVEL) is driven to the
appropriate level to set the calibrated laser diode output
power level.
3. The feedback loop is closed for calibration (CAL = logic
LOW, and PULSE = logic HIGH), and then opened (CAL
= logic HIGH).
4. While the feedback loop is open, the laser is pulsed on and
off by PULSE.
5. The feedback loop is periodically recalibrated as needed.
6. The AD9661A is disabled when the laser will not be pulsed
for an indefinite period of time.
AD9661A
Control Loop Transfer Function
The relationship between IMONITOR and VPOWER LEVEL is
I MONITOR
=
VPOWER LEVEL –
(RGAIN + 50
VREF
Ω)
once the loop is calibrated. When the loop is open (CAL = logic
HIGH), the output current, IOUT, is proportional to the held
voltage at HOLD; the external hold capacitor on this pin
determines the droop error in the output current between
calibrations.
The sections below discuss choosing the external components in
the feedback loop for a particular application.
Choosing RGAIN
The gain resistor, RGAIN, allows the user to match the feedback
loop’s transfer function to the laser diode/photo diode
combination.
The user should define the maximum laser diode output power
for the intended application, PLD MAX, and the corresponding
photo diode monitor current, IMONITOR MAX. A typical laser
diode transfer function is illustrated below. RGAIN should be
chosen as:
RGAIN
=
1.6V
I MONITOR MAX
– 50 Ω
4
0°C CASE
3
CONSTANT WRITE POWER
2
25°C
CASE
50°C CASE
1
0
0 20 40 60 80 100 120
FORWARD CURRENT – mA
IOUT
Figure 2. Laser Diode Current-to-Optical Power Curve
DISABLE
POWER-UP
OR LASER
NOT IN USE
CAL
CAL
TIME
RECALIBRATE
HOLD TIME
PULSE
CALIBRATED LEVEL
LASER
OUTPUT POWER
LASER POWER
MODULATED
Figure 1. Normal Operating Mode
REV. 0
–5–
5 Page 
AD9661A
AD9661A EVALUATION BOARD
The AD9661A Evaluation Board is comprised of two printed
circuit boards. The Laser Diode Driver (LDD) Resource Board
is both a digital pattern generator and an analog reference gen-
erator (see LDD Resource Board Block Diagram.) The board is
controlled by an IBM compatible personal computer through a
standard printer cable. The resource board interfaces to the
AD9661A DUT board, which contains the AD9661A, a level
shift circuit for the analog input, and a socket for an N type
laser diode. A dummy load circuit for the laser diode is in-
cluded for evaluation. Power for all the boards is provided
through the banana jacks on the AD9661A DUT board.
These should be connected to a linear, +5 V power supply.
Schematics for the LDD Resource Board, AD9661A DUT,
and Dummy Load are included, along with a bill of mate-
rial and layout information. Please contact Applications for
additional information.
STANDARD PARALLEL
PRINTER CABLE
IBM-COMPATIBLE
PC
WITH WINDOWS
PARALLEL
PRINTER PORT
P1
CENTRONICS
CONNECTOR
40MHz
CLOCK
OSCILLATOR
32K x 16
MEMORY
READBACK
LATCH
ADDRESS
COUNTER
AND
RESOURCE
CONTROLLER
DIGITAL PATTERN GENERATOR
8 DAC 1
0–2.55V
X1
8 DAC 2
X1 0–2.55V
ANALOG REFERENCE
LASER DIODE DRIVER RESOURCE BOARD
PULSE
WIDTH
MODULATOR
(AD9560)
OUTPUT
BUFFER
OUTPUT
SMB
CONNECTORS
J4 PULSE1 (JPUL)
J5 CAL (JCALB)
J7
J8
DISABLE (JDIS)
PULSE2 (JPULB)
J6
J2
UNUSED
TRIGGER
J3
INTERFACE TO
AD9661A
EVALUATION
BOARD
12
11 EXTERNAL LEVEL SHIFT CIRCUIT
AD9661A
R9 R8 LEVEL SHIFT IN
20-PIN
HEADER
17–20
+5V POWER SUPPLY
1–10
GROUND
Figure 10. LDD Resource Board Block Diagram
INPUT SMB CONNECTORS
FOR DIGITAL CONTROLS
5
AD9661A
20
20-PIN HEADER
FOR ANALOG
CONTROLS
OPTIONAL
LEVEL SHIFT
CIRCUIT
DUMMY LOAD CIRCUIT/
LASER DIODE SOCKET
AD9661A
EVALUATION BOARD
Figure 11. Evaluation Board Block Diagram
REV. 0
–11–
11 Page | ||
| Páginas | Total 12 Páginas | |
| PDF Descargar | [ Datasheet AD9661A.PDF ] | |
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