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LDTC0520 / LDTC1020
PAGE 14
LDTC1020-00400-A Rev B
WTC OPERATION, continued
4. PROPORTIONAL GAIN AND
INTEGRATOR TIME CONSTANT -
PI
TERMS
The default settings of The LDTC are confi gured
to the mid-range positions appropriate for most
laser diode loads. To adjust these parameters to
optimize the temperature control system time to
temperature or stability, contact Wavelength.
5. Attaching VDD_WTC and VS
Power Supplies
The VDD_WTC input supplies voltage to the
control electronics of the WTC only. Separate
inputs are provided for both the FL control
electronics and the output stage of the WTC.
The supply should be capable of providing at
least 200 mA of current in applications that
use separate VS and VDD_FL supplies in the
temperature control implementation. Temperature
control applications that tie the three supply inputs
together require current capacity that equals
the sum of the maximum TEC or Resistive
Heater current, plus the maximum laser diode
current, plus approximately 200 mA for the
control electronics of the WTC3243 Temperature
Controller and the FL500 Laser Driver, plus
current to an optional fan. The maximum current
required by the LDTC will be 3.5 amps or less.
VS is the voltage that is applied to the TEC
or resistive heater. This voltage should be high
enough to supply the voltage required by the TEC
or resistive heater plus the voltage drop across
the WTC. The voltage available to the TEC will
be from between 0.5 to 1.8V lower than VS,
depending on the output current. To minimize
power dissipation in the WTC, keep VS as low as
possible.
An online Safe Operating Area (SOA) calculator
is available for the WTC3243. Calculate the
maximum power dissipation of your design at
http://www.teamwavelength.com/toolscalculator/
soa/defaulttc.htm
before applying power to the
LDTC.
6. TEMPERATURE SETPOINT
The temperature setpoint can be either remotely
or locally controlled. An on-board trimpot (TSET)
will adjust the voltage from 0.3V to 2.5V.
Additionally, Pin 11 (EXT T SET) & 12 (COM) of
Connector 2 will accept an external voltage (from
0.3 to 2.5V). The “Failsafe Setpoint” will default
the setpoint to 1V (~25°C for a 10k
Ω
thermistor)
if the chosen signal (from potentiometer or remote
setpoint) falls below 0.3V. There is about 100mV
of hysteresis built into the default voltage.
A dip switch set lets you choose to use only the
on-board potentiometer or the external voltage.
Position 3 on the switchbank above J3 confi gures
the Remote Temperature Setpoint choice.
The input impedance of the EXT T SET is greater
than 20k
Ω
and is fully buffered.
If you use a different sensor or would prefer a
different default voltage, contact Wavelength.
Figure 6
Source of setpoint
LDREF
C
C
| CP
TREF
EXT
INT
LDREF
C
C
| CP
TREF
EXT
INT
Use Onboard
Trimpot Only
Use External
Voltage Only
