© 2022
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WTC32ND TEMPERATURE CONTROLLER
SAFETY INFORMATION
& THERMAL DESIGN
CONSIDERATIONS
SAFE OPERATING AREA — DO NOT EXCEED
INTERNAL POWER DISSIPATION LIMITS
!
To ensure safe operation of the WTC32ND
Temperature Controller, it is imperative
that you determine that the unit will be
operating within the internal heat dissipation
Safe Operating Area (SOA).
Visit the Wavelength Electronics website for the most
accurate, up-to-date, and easy to use SOA calculator:
www.teamwavelength.com/support/design-tools/soa-tc-calculator/
For more information on Safe Operating Area, see our
Application Note
AN-LDTC01: The Principle of the Safe
.
PREVENT DAMAGE FROM ELECTROSTATIC
DISCHARGE
Before proceeding, it is critical that you take precautions to
prevent electrostatic discharge (ESD) damage to the driver
and your laser. ESD damage can result from improper
handling of sensitive electronics, and is easily preventable
with simple precautions.
For more information on ESD, see Application Note
AN-LDTC06: Basics: Electrostatic Discharge (ESD)
We recommend that you always observe ESD precautions
when handing the WTC controller.
THEORY OF OPERATION
The WTC32ND is a linear temperature controller that delivers
bidirectional current to Peltier Effect thermoelectric coolers
(TEC), or unidirectional current to resistive heaters.
The fundamental operating principle is that the controller
adjusts the TEC drive current in order to change the
temperature of the sensor that is connected to the thermal
load. The goal is to make the voltage across the sensor match
the setpoint voltage, and then keep them equal in spite of
changes to ambient conditions and variations in thermal load.
The controller measures the load temperature by driving a
current through the temperature sensor and measuring the
voltage drop across it. It may be useful to remember that you
do not directly adjust the setpoint temperature. Rather, you
adjust a voltage signal that represents the sensor voltage at
the desired temperature setpoint.
While the output is enabled the controller continuously
compares the setpoint voltage and the actual sensor voltage.
If there is a difference between the two signals the controller
adjusts the output current—thereby driving the TEC or heater
to change temperature—until the difference is zero.
Once the actual sensor voltage equals the setpoint voltage,
the controller makes minor adjustments to the output
current in order to keep the difference at zero. If the ambient
temperature changes, for example, the controller will adjust
the drive current accordingly.
The controller includes features that help protect the load
from damage, and also make it more versatile in a wide array
of applications. These features are explained in detail in
Operating Instructions — W EVAL BOARD on
• Current limit:
Independent heating and cooling current
limits avoid over-driving and damaging the TEC or heater.
•
External or Onboard temperature setpoint control:
for
prototyping and benchtop applications the temperature
setpoint can be adjusted with the onboard trimpot on the
evaluation board. When the controller is integrated into an
automated control system, the temperature setpoint can
be adjusted by an external voltage signal.
• Local Enable on WTC32ND-EV Evaluation Board:
the
controller can be configured so that the output is always
on whenever power is applied to the unit.
• Control loop:
the controller employs a smart Proportional-
Integrating control loop to adjust the drive current. The
proportional term is user-adjustable, and when properly
configured will quickly settle the load to temperature with
minimal overshoot and ringing.
