AD9660KR Analog Devices Inc, AD9660KR Datasheet - Page 9

• 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

REV. 0
Example Calculations
The example below (in addition to the one included in the sec-
tions above) should guide users in choosing R
hold capacitor values, and worst case calibration times.
System Requirements:
Laser diode/photo diode characteristics:
Bias laser power: 4 mW Bias
Write laser power: 25 mW
Bias Hold Time: 1 ms
Write Hold Time: 1 s
Laser efficiency 0.5 mA/mA
Monitor current: 5 A/mA
From the laser power requirements and efficiency we can
estimate:
Choosing hold caps based on these:
and
The bias loop initial calibration time for a <1% error:
5 = 5
Bias loop recalibration for a 1% error after 5% droop (need to
correct within 20%):
2 = 2
The write loop initial calibration time for <0.1% error:
7 = 7
Write loop re-calibration for a 0.1% error after 0.5% droop
(need to correct within 20%):
2 = RC = 2
C
C
and
I
I
WRITE HOLD
BIAS HOLD
WRITE MAX
BIAS MAX
RC = 5
RC = 2
RC = 7
4 mW
18 10
140
25 mW
18 10
550
140
550
400 A
250 A
(5%) / 0.5
9
72 pF = 20.2 ns
9
1 ms
0.5% / 0.5
0.045 F = 123.75 s
0.045 F = 12.6 s
72 pF = 277.2 ns
1 s
0.5%
5%
0.045 F
72 pF
mW
mA
mW
mA
GAIN
400.0 A
, C
250 A
GAIN
, the
–9–
Driving the Analog Inputs
The BIAS LEVEL and WRITE LEVEL inputs of the AD9660
drive the track and hold amplifiers and allow the user to adjust
the amount of output current as described above. The input
voltage range on both inputs is V
the user to create an offset of V
The circuit in Figure 9 will perform the level shift and scale the
output of a DAC whose output is from ground to a positive
voltage. This solution is attractive because both the DAC and
the op amp can run off a single +5 V supply, and the op amp
doesn’t have to swing rail to rail.
From the monitor current specification and the max power
C
specified:
and
I
R
MONITOR MAX
GAIN
GAIN
DAC1
DAC2
would be chosen as 2 pF (see Table I).
1.85 I
Figure 9. Driving the Analog Inputs
V
V
DAC2
DAC1
R3
R1
25 mW
MONITOR MAX
1.6 V
R2
R4
R3
R1
5 A
mW
REF
REF
OP291
OP291
V
V
R2
R4
REF
REF
for a ground based signal.
+5V
125 A
to V
50
+ V
+ V
DAC1
DAC2
REF
R2
R1
R4
R3
+ 1.6 V, requiring
6.9 k
= V
= V
AD9660
BIAS LEVEL
V
WRITE LEVEL
BIAS LEVEL
WRITE LEVEL
REF
AD9660