© 2018
10
LDTC2/2 LASER DIODE DRIVER AND TEMPERATURE CONTROLLER
POWER SUPPLY SELECTION
The V
DD
voltage supply input is common to both the WLD3343
and the WTC3243. This supply furnishes the voltage to the
control electronics of the devices as well as the compliance
voltage for the WLD3343 laser driver.
The supply should be capable of providing at least 3.0 A
of current in applications that use a separate V
S
supply
in the temperature control implementation. Temperature
control applications that tie V
DD
and V
S
together require a
V
DD
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
WLD3343 laser driver, plus current to an optional fan. Using
the maximum potential of the WLD and WTC will not require
more than 6.0 A.
V
S
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
compliance required by the WTC. The voltage available to
the TEC will be from between 0.5 to 1.8 V lower than V
S
. To
minimize power dissipation in the WTC, keep V
S
as low as
possible.
Calculate the maximum internal power dissipation of your
design
before applying power to the LDTC2/2
. There are
Safe Operating Calculators available on our website.
TEMPERATURE SETPOINT
Wavelength introduces a special setpoint circuit with the
LDTC2/2. An onboard trimpot (TSET) will adjust the voltage
from 0.3 to 2.5 V. Additionally, Pins 11 (R TC SET) &
12 (COM) of Connector J2 will accept a DAC voltage (from
0.3 to 2.5 V). The new feature - the “Failsafe Setpoint” will
default the setpoint to 1 V (~25°C for a 10 kΩ thermistor) if
the chosen signal (from the onboard trimpot or DAC) falls
below 0.3 V.
A jumper (ExtTset) lets you choose to use only the
on-board potentiometer or the external voltage, as shown in
below.
Use On-board
trimpot
OR
Sum ExtTset with
trimpot
CC
CP
S2
CC
CP
S2
Use External
Voltage only
ExtTset
Vset PDset
ExtTset
Vset PDset
Figure 7. Source of setpoint.
The ExtTset jumper configures the Remote Temperature
Setpoint choice. There is approximately 100 mV of
hysteresis built into the default voltage. The input impedance
of R TC SET is greater than 20 kΩ and is fully buffered. If
you use a different sensor or would prefer a different default
voltage, contact Wavelength.
MONITOR ACTUAL TEMPERATURE & SETPOINT
Pins 9 & 10 of Connector J2 are ACT T MONitor
and SET T MONitor, respectively. Measure the actual
sensor voltage across Pin 9 and Pin 12 (COM). For a 10 kΩ
thermistor with the default 100 μA bias current, the resistance
(in kΩ) is given by:
R = 10
·
V
J2_PIN9
To monitor the setpoint voltage used by the WTC, use Pins
10 and 12.
ENABLE CURRENT TO TEC
Output current is supplied to the load as soon as power is
applied to the controller. The Power LED indicator will light
GREEN when power is applied.
