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© 2001-2013
WLD3343
PAGE 9
WLD3343-00400-O
1. SELECTING THE LASER DIODE
OUTPUT CURRENT RANGE
The output current range of the WLD3343
depends on the selection of resistor R
SENSE
placed between
P
in 8 (RS+) and Pin 10 (RS-) as
shown in Figure 3.
Equation 1 calculates R
SENSE
for a maximum
desired laser diode current, I
LDMAX.
Refer to
Table 1 to select R
SENSE
for common laser diode
current ranges.
2. HELPFUL HINTS FOR CHOOSING
R
SENSE
• Never use a carbon
fi
lm resistor for R
SENSE.
• Avoid resistors with high parasitic inductance.
• Select a resistor with a low temperature
coef
fi
cient (1%
≈
100ppm/
˚
C).
• Place R
SENSE
as close to Pins 8 (RS+) and
10 (RS-) on the WLD3343 as possible to
avoid parasitic resistance effects from the
PCB layout.
• Use Equation 2 for determining the power
rating of R
SENSE.
Note:
Wavelength Electronics recommends
a conservative power rating of 2 times normal
maximum for R
SENSE.
Equation 2 incorporates
this recommendation.
Table 1
Laser Diode Current Sense Resistor
R
SENSE
vs Maximum Laser Diode Current
I
LDMAX
Figure 3
Connecting R
SENSE
Equation 1
Calculating R
SENSE
Constant Power Mode
R
SENSE
=
1.25
I
LDMAX
OPERATION
Equation 2
Calculating The Power Rating
For R
SENSE
RATING = 2 * I
2
LDMAX
* R
SENSE
TYPE A / B Laser Diodes
A
B
GND
V
DD
11
9
10
14
WLD3343
LD
R
SENSE
8
7
RS+
RS-
I
LD
TYPE C Laser Diodes
A
B
GND
V
DD
11
9
10
14
WLD3343
LD
R
SENSE
8
7
RS+
RS-
I
LD
Constant Current Mode
R
SENSE
=
1.00
I
LDMAX
Constant Current
Current
Sense
Resistor,
R
SENSE
Maximum
Output
Current
I
LDMAX
Constant Power
Current
Sense
Resistor,
R
SENSE
50 mA
125 mA
250 mA
500 mA
1.25 Amps
2.2 Amps
3 Amps
25.00
10.00
5.00
2.50
1.00
0.57
0.42
20.00
8.00
4.00
2.00
0.80
0.45
0.33
An online tool is available
to determine values for external components:
http://www.teamwavelength.com/support/tools.asp
.
