© 2018
13
LDTC0520 / LDTC1020 LASER DIODE AND TEMPERATURE CONTROLLER
OPERATING INSTRUCTIONS
LASER DRIVER
Wavelength recommends that initial wiring and configuration
of the LDTCxx20 be performed with test loads in place of
the laser. Using test loads reduces the risk of damaging
expensive components, and can make the configuration
process simpler.
The configuration sequence is as follows:
• Connect the power supply and test load
• Set the current drive limit
• Replace the test load with your laser diode
• Adjust the laser drive setpoint
•
Configure for external or local (internal) control
• Adjust the current setpoint and monitor the driver
WIRE THE LASER DRIVER POWER SUPPLY
AND TEST LOAD
The current limit is set with the driver in Constant Current
mode and can be set in two ways; the method described
here is done with the cover on the LDTC but requires the
output current be enabled. An alternate method is presented
on
Leave in place all the components that were connected
during the temperature controller configuration, and now
wire the laser driver power supply per
.
VDD_FL
VDD_WTC
VS
GND
SP1
SP2
LD SHD (Enable LD current)
COM
EXT LD SETpoint
COM
LD P Monitor
LD I Monitor
ACT T Monitor
SET T Monitor
EXT T SETpoint
COM
J1
J2
V
DD_FL
1
1
4
12
DMM
Figure 13. Laser Driver Power Supply and
Monitor Wiring
Next wire the laser driver test load; refer to
. With
the test loads, to stay within the Safe Operating Area, VS
must not exceed 5 V.
LDC
PDA
Spare
LDA
COM
TEC+
TEC-
SEN+
SEN-
COM
J3
1
10
1N4001
(2x req’d)
1 Ω, 2 W
Figure 14. Laser Driver Test Load Wiring
SET THE LASER DRIVER CURRENT LIMIT
Refer to the laser diode datasheet to determine the maximum
allowable drive current (I
LIM
). Measure the exact resistance
of the test load (R
LOAD
), then calculate the V
LIM
voltage drop
across the test load resistor:
V
LIM
= I
LIM
· R
LOAD
(1)
Set the I SET trimpot to zero by turning fully counter-
clockwise at least 12 turns; set the I LIM trimpot to full-scale
by turning it clockwise at least 12 turns. Set the CC | CP
switch to CC.
Switch on the VDD_FL power supply; the FL POWER LED
will illuminate green. Set the onboard laser output switch
to EN to enable the current; the LD EN LED will illuminate
green.
Adjust the I SET trimpot clockwise until the voltage on the
LD I Monitor pins (pin J2‑8 to J2‑6) matches the V
LIM
value
calculated above. Now adjust the I LIM trimpot down by
turning counter-clockwise until the voltage on the voltmeter
starts to change. Now the limit is set at the maximum desired
operating current.
Measure the voltage on the LD I MON pin; it should
correspond to the desired limit current value. Refer to
for the LD I MON transfer function for your LDTC
model, and verify that the drive current is correct using this
equation:
I
LD
= V
LDMON
· Transfer Function
(2)
Adjust the I SET trimpot counter-clockwise to zero the
setpoint current. Set the enable switch to DIS to disable
the output current, and switch off the V
DD_FL
power supply.
Remove the test load.
To practice using the driver in Constant Power mode, refer to
for the Constant Power test circuit.
WIRE THE LDTC FOR YOUR LASER DRIVER
APPLICATION
If you are comfortable with the operation of the LDTC laser
driver, connect your laser diode per
This figure also shows how to connect the optional external
enable switch and external setpoint signal source. Example
setpoint circuits are shown on
. The transfer
function for the EXT LD SET input is shown in
!
Do not insert or remove the laser diode from
the circuit while power is applied to the LDTC.
The laser diode may be damaged or destroyed.
