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WLD3393
PAGE 12
WLD3393-00400-K
STEP 10: ADJUST THE SETPOINT VOLTAGE
The setpoint controls the output of the WLD3343. In constant current mode the setpoint is directly
proportional to the laser diode current. In constant power mode the setpoint is directly proportional to
photodiode current, allowing for control of the power of the light emitted from the laser diode.
The setpoint voltage can be adjusted either by using the onboard SET trimpot, by applying an external
setpoint voltage, or by summing an external setpoint voltage with the setpoint dialed in using the SET
trimpot. The sum of the external setpoint voltage and the value dialed in using the SET trimpot can be
adjusted from 0 to 2.5 V.
To use only the onboard SET trimpot
, place the VSET SOURCE jumper on the bottom of the WLD3393
evaluation board in the “
T
” position, and do not connect an external voltage source to the SET terminal
on the terminal block. The SET trimpot will allow the setpoint to be adjusted from 0 V to 2.5 V. Figure 4
shows the jumper location.
To use an external voltage source summed with the setpoint voltage from the onboard SET trimpot
,
place the VSET SOURCE jumper on the bottom of the WLD3393 to the “
T
” position. Connect an
external voltage source to the SET terminal on the terminal block on the top of the WLD3393 evaluation
board. The resulting setpoint voltage will be the sum of the voltage dialed in using the SET trimpot, and
the voltage applied to the SET terminal. Figure 4 shows the jumper location.
To use only an external voltage source for the setpoint
, place the VSET SOURCE jumper on the
bottom of the WLD3393 board to the “
X
” position and connect the external setpoint voltage source
to the SET terminal on the terminal block on the top side of the WLD3393 evaluation board. When
the SET SOURCE jumper is in the “
X
” position, the voltage dialed in using the SET trimpot on the
WLD3393 is ignored. Figure 4 shows the jumper location.
In case an external voltage source is not available, but setpoint adjustment needs to be external, a
remotely located potentiometer can easily be connected to the WLD3393 to adjust the setpoint. To use
a remote potentiometer, connect the CW lead of the potentiometer to the terminal position marked 2.5
on the terminal block on the top of the WLD3393 board. Connect the CCW lead of the potentiometer
to the COM terminal and connect the wiper to the SET terminal and ensure that the VSET SOURCE
jumper on the bottom of the board is set to the “
X
” position. See Figure 7 for external potentiometer
wiring.
200 mA Range
2.0 Amp Range
LDI = V
SET
* 106 [ mA / V]
LDI = V
SET
* 1.2 [ A / V ]
Table 5: Laser Diode Current (LDI) vs. V
SET
200
μ
A Range
2 mA Range
PDI = V
PMON
* 100 [
μ
A / V ]
PDI = V
PMON
[ mA / V ]
Table 6: Photodiode Current (PDI) vs. V
SET
Figure 7 - External Setpoint Adjustment
(-)
(+) FAN
PMON
SET
2.5
PDM
COM
IMON
W
CW
CCW
NOTE: The 2.5 V output can source 1.5 mA with
a 5 V input. Use greater than 2 k
Ω
resistance to
prevent loading it down.
CONFIGURING THE EVALUATION BOARD
