AD9660KR Analog Devices Inc, AD9660KR Datasheet - Page 6

• Manufacturer Part Number: AD9660KR
• Description: IC LASER DIODE DRIVER 28-SOIC
• Manufacturer: Analog Devices Inc
• Type: Laser Diode Driverr

Specifications of AD9660KR

• Number Of Channels: 1
• Rohs Status: RoHS non-compliant
• Voltage - Supply: 4.75 V ~ 5.25 V
• Current - Supply: 110mA
• Current - Modulation: 60mA
• Current - Bias: 90mA
• Operating Temperature: 0°C ~ 70°C
• Package / Case: 28-SOIC (0.300", 7.50mm Width)
• Mounting Type: Surface Mount
• Operating Temperature (max): 70C
• Operating Temperature (min): 0C
• Mounting: Surface Mount
• Operating Temperature Classification: Commercial
• Lead Free Status / RoHS Status: Compliant

AD9660
The disable circuit turns off I
voltages to their minimum levels (minimum output current)
when DISABLE = logic HIGH. It is used during initial power-
up of the AD9660 or during time periods when the laser is inac-
tive. When the AD9660 is re-enabled the control loops must be
recalibrated.
Normal operation of the AD9660 involves (in order, see figure):
1. The AD9660 is enabled (DISABLE = logic LOW).
2. The input voltages (BIAS LEVEL and WRITE LEVEL) are
3. The bias loop is closed for calibration (BIAS CAL = logic
4. The write loop is closed for calibration (WRITE PULSE and
5. While both loops are open, the laser is pulsed between the
6. The bias and write loops are periodically recalibrated as
7. The AD9660 is disabled when the laser will not be pulsed for
Control Loop Transfer Functions
The relationship between I
once the bias loop is calibrated. When the bias loop is open
(BIAS CAL = logic LOW), its output current, I
tional to the held voltage at BIAS HOLD; the external hold ca-
pacitor on this pin determines the droop error in the output bias
current between calibrations.
The relationship between I
once the write loop is calibrated. The current supplied by the write
loop output is referred to as the modulation current, I
driven to the appropriate levels to set the calibrated laser di-
ode output power levels.
HIGH), and then opened (BIAS CAL = logic LOW).
WRITE CAL = logic HIGH) and then opened.
two calibrated levels by WRITE PULSE.
needed.
an indefinite period of time.
I
I
MONITOR
MONITOR
OUTPUT POWER
WRITE PULSE
WRITE CAL
BIAS CAL
1.85 (R
1.85 (R
DISABLE
V
V
LASER
WRITE LEVEL
BIAS LEVEL
MONITOR
MONITOR
OUT
NOT IN USE
POWER-UP
OR LASER
GAIN
GAIN
CALIBRATED WRITE
CALIBRATED BIAS
and returns the hold capacitor
and V
and V
V
V
50
50
REF
REF
BIAS
TIME
CAL
BIAS LEVEL
WRITE LEVEL
)
)
WRITE
LOOP
TIME
CAL
BIAS
Figure 4. Normal Operating Mode
, is propor-
MODULATION
BIAS AND WRITE LEVELS
is
is
LASER POWER
MODULATED
WRITE LOOP
HOLD TIME
BETWEEN
RECALIBRATE WRITE LOOP
.
–6–
RECALIBRATE THE BIAS LOOP
When the write loop is open (WRITE CAL logic LOW),
I
The external hold capacitor (WRITE HOLD) determines the
droop error between calibrations. I
on and off by WRITE PULSE when the write loop is open.
The sections below discuss choosing the external components in
the feedback loops for a particular application.
Choosing R
The gain resistor, R
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, P
photo diode monitor current, I
ode transfer function is illustrated in Figure 5. R
chosen as:
The laser diode’s output power will then vary from 0 to P
for an input range of V
and WRITE LEVEL inputs.
MODULATION
Figure 5. Typical Laser Diode Current-to-Optical
Power Curve
4
3
2
1
0
R
0
GAIN
is proportional to the held voltage at WRITE HOLD.
GAIN
BIAS CALIBRATION POWER
CONSTANT WRITE POWER
20
GAIN
1.85 I
REF
, allows the user to match the feedback
FORWARD CURRENT – mA
40
to V
BIAS
1.6 V
MONITOR MAX
LD MAX
MONITOR MAX
REF
60
MODULATION
+1.6 V @ the BIAS LEVEL
, and the corresponding
80
MOD
0 C CASE
. A typical laser di-
50
may be switched
50 C CASE
100
GAIN
.
CASE
25 C
should be
120
REV. 0
LD MAX