© 2018
15
LDTC2/2 LASER DIODE DRIVER AND TEMPERATURE CONTROLLER
CHANGING THE LASER DIODE OUTPUT
CURRENT RANGE
The output current range of the WLD3343 depends on
the selection of resistor R
SENSE
. Two 2520-sized resistors
combine in series to produce this total R
SENSE
resistance
(R14 & R15). See
for their location.
R
SENSE
= R
14
+ R
15
The LDTC2/2 defaults the maximum range to 2.2 A. To
change the range, and the sensitivity of the setpoint voltage,
use
, or
, and install the
appropriate R
SENSE
resistance.
Table 5. Laser Diode Current Sense Resistor R
SENSE
vs.
Maximum Laser Diode Current I
LDMAX
MAXIMUM OUTPUT
CURRENT
I
LDMAX
CONSTANT
POWER
R
SENSE
CONSTANT
CURRENT
R
SENSE
50 mA
25.00 Ω
20.00 Ω
125 mA
10.00 Ω
8.00 Ω
250 mA
5.00 Ω
4.00 Ω
500 mA
2.50 Ω
2.00 Ω
1.25 Amps
1.00 Ω
0.80 Ω
2.2 Amps
0.57 Ω
0.45 Ω
Equation 7. Calculating R
SENSE
for Constant Power Mode.
R
SENSE
=
1.25
I
LDMAX
Equation 8. Calculating R
SENSE
for Constant Current Mode.
R
SENSE
=
1.00
I
LDMAX
Helpful hints for choosing R
SENSE
:
•
Never use a carbon film resistor for R
SENSE
.
• Avoid resistors with high parasitic inductance.
•
Select a resistor with a low temperature coefficient (1%,
<100 ppm/°C).
• Use
for determining the power rating of
R
SENSE
.
Equation 9. Calculating the Power Rating for R
SENSE
.
RATING = 1.25
·
(I
LDMAX
)
2
·
R
SENSE
1
J2
12
11
10
9
8
7
6
5
4
3
2
1
R
SENSE
= R
14
+ R
15
R14
R15
Figure 12. Location of R
SENSE
