© 2018
11
WLD SERIES LASER DIODE DRIVERS
CONFIGURE THE LASER DIODE CURRENT
LIMIT
The WLD3343 allows a customized current range for
a specific application. This allows optimized setpoint
resolution while minimizing output noise. The current limit
is set by properly choosing the limit resistor (R
LIM
) and
installing it between Pins 6 and 7.
There are two methods of choosing the appropriate
resistance value R
LIM
. The first uses the
normalized
maximum output current
. The second is a
calculation using
Equation
. Both methods depend on
the laser diode type and mode of operation.
Method 1:
To find the normalized maximum output current, divide the
desired laser diode current limit (I
LDLIM
) by the maximum
laser diode current (I
LDMAX
), as shown in
Equation
.
Then, choose the resistance value of R
LIM
shown next to the
calculated normalized maximum output current in
I
MAX,NORM
=
I
LDLIM
(6)
I
LDMAX
For example, consider using a Type A/B laser diode in
Constant Current mode. If the WLD is configured to output
a maximum current of 2.2 A, and the user wishes to set the
limit current at 1.5 A, then the normalized maximum output
current is 0.68 (1.5/2.2). This value then yields a value of
R
LIM
equal to 405 Ω (from
)
Method 2:
To precisely calculate the value of R
LIM
, use
Equation
,
R
LIM
=
α
I
LDLIM
R
SENSE
+1
(7)
β
1-
I
LDLIM
R
SENSE
+1
β
LASER DIODE TYPE
–
MODE
α
β
Type A/B – CC
282
2.85
Type A/B – CP
350
3.35
Type C – CC
290
2.93
Type C – CP
385
3.57
Table 4. Values of
α
and
β
to calculate R
LIM
given laser
type and operation mode.
Setting Current Limits Using Trimpots
Connect a 500 Ω trimpot and a 150 Ω resistor as shown in
to make the maximum current limit adjustable.
GND
7
WLD3343
R
LIM
6
LIM
CW
CCW
W
150
Ω
500
Ω
SINGLE TURN
TRIMPOT
Figure 5.
Use the configuration shown for adjustable current
limits.
I
MAX,NORM
TYPE A/B
CC
R
LIM
(
Ω
)
TYPE A/B
CP
R
LIM
(
Ω
)
TYPE C
CC
R
LIM
(
Ω
)
TYPE C
CP
R
LIM
(
Ω
)
0.00
152
149
150
150
0.04
162
160
160
160
0.08
172
171
169
171
0.12
183
183
179
183
0.16
194
195
190
195
0.20
205
208
201
207
0.24
217
222
213
220
0.28
230
236
225
234
0.32
243
251
238
248
0.36
257
267
251
263
0.40
272
284
265
279
0.44
288
301
280
295
0.48
305
320
296
313
0.52
322
340
313
331
0.56
341
361
330
350
0.60
361
383
349
370
0.64
382
406
369
392
0.68
405
432
390
414
0.72
429
459
412
438
0.76
455
488
436
463
0.80
483
519
462
490
0.84
514
552
490
519
0.88
547
588
519
550
0.92
582
627
551
583
0.96
621
670
586
618
1.00
664
716
624
656
Table 5. Choose R
LIM
as a function of normalized
maximum output current, laser diode type, and operation
mode.
Use the online WLD Circuit Calculator to automatically determine
values for external components.