www.teamWavelength.com
© 2001-2013
WLD3343
PAGE 10
WLD3343-00400-O
Example 1
Choosing R
LIM
for a Type A/B Laser Diode
with a 1.5 A Maximum Forward Current in
Constant Current Mode.
Con
fi
gure the WLD3343 so that I
LDMAX
is 2.2 A by
selecting R
SENSE
equal to 0.45
. The Normalized
Maximum Output Current then equals:
A Normalized Output Current of 0.68 (68%)
corresponds to a current limit set resistor R
LIM
of
405
.
3. CONFIGURING THE LASER DIODE
CURRENT LIMIT
The WLD3343 allows a customized current range for
a speci
fi
c application. This allows optimized set point
resolution while minimizing output noise. Table 2 (next
page) lists the scaling factors for different current limits
(R
LIM
).
To select an appropriate resistance value for the limit
resistor (R
LIM
), the laser diode type and mode of
operation, divide the maximum laser diode current
(determined in Section 1) into the desired maximum
operating current for the laser diode. This result is the
Normalized Maximum Output Current. Choose the
resistance value of the current limit set resistor (R
LIM
)
shown next to the calculated Normalized Maximum
Output Current.
Use Equation 3 to calculate a precise value
for R
LIM
.
Setting Current Limits Using Trimpots
Connect a 500
trimpot and a 150
resistor as
shown in Figure 4 to make the maximum current limit
adjustable.
Figure 4
Adjustable Current Limits
Equation 3
Calculating R
LIM
=
=
1.5 Amps
2.2 Amps
0.68
α
I
LDLIM
R
SENSE
+1
I
LDLIM
R
SENSE
+1
β
R
LIM =
β
1-
GND
7
WLD3343
R
LIM
6
LIM
CW
CCW
W
150
:
500
:
SINGLE TURN
TRIMPOT
OPERATION
Laser Diode Type / Mode
Type A/B - CC
Type A/B - CP
Type C - CC
Type C - CP
282
350
290
385
2.85
3.35
2.93
3.57
An online tool is available
to determine values for external components:
http://www.teamwavelength.com/support/tools.asp
.
