© 2022
17
WTC3243 TEMPERATURE CONTROLLER
ATTACH THE VDD AND VS POWER SUPPLIES
The V
DD
power supply is used to power the WTC3243
internal control electronics and must be capable of
sourcing a minimum of 8 mA of current. If a fan is needed,
the fan draw current on V
DD
will also need to be added
to the minimum required current. The V
S
power supply is
used to power the WTC3243 output stage and must be
capable of supplying a current greater than the Limit A
(LIMA) and Limit B (LIMB) current limit settings.
For simple operation, set the Power Supply Jumper to “1”
or Single Supply Operation (see
) and then use
the power jack. The power jack is tied to V
DD
. To separate
the supplies, set the Power Jumper to “2” or Dual Supply
Operation and use either the terminal block (TB1) alone
or a combination of the power jack and VS on TB1.
Use PGND for the power return. The common (COM)
terminal on the WTC3293 is not intended to act as a
power connection, but as a low noise ground reference
for monitor signals.
A separate power supply allows the output stage to
operate at a voltage lower than the V
DD
supply or up to the
+30 V maximum. Select V
S
approximately 1.0 Volt above
the maximum voltage drop across Output A (OUTA) and
Output B (OUTB), which is also the voltage across the
thermoelectric controller, to reduce the power dissipation
on the WTC3243 component and minimize the heatsinking
requirements. When sizing the power supply, take the
temperature controller, load, and heatsink components
into consideration.
The 2.5 mm input power jack is attached to V
DD
. You can
use the Wavelength PWRPAK power supplies with this
jack. Use either the power jack or the power inputs on
TB1, not both.
The COMMON (COM) terminal on the WTC3293 is
not intended to act as a power connection, but as a
low noise ground reference for monitor signals.
Once power is connected to the Evaluation
Board, all control electronics are powered,
however there is no drive current available to
other components until the WTC3293 Enable
switch is ON.
CONFIGURE THE HEAT AND COOL LIMITS
The WTC3293 Limit A (LIMA) and Limit B (LIMB) trimpots
independently adjust the heat and cool current limits from
zero to a full 2.2 A.
Use
to calculate the voltage at LIMA or LIMB
corresponding to the desired limit current (I
LIM
).
Equation 5.
Calculating LIMA or LIMB from I
LIM
LIM = (0.3 * I
LIM
) + 1
Where:
LIMA or LIMB is in Volts (V)
I
LIM
is the desired maximum output current, in Amps (A)
Once the LIMA and LIMB values are determined, toggle
the ENABLE to ON to apply power to V
DD
and V
S
(no load
required). Rotate LIMA or LIMB trimpot and monitor the
respective voltage at LIMA and LIMB on TB3. Use COM as
ground reference. Turn the trimpots counter-clockwise to
reduce the limits or clockwise to increase them.
Use
to determine which limit trimpot sets the heating
and cooling limits based on the sensor and load type.
Table 6. LIMA and LIMB Current Limit Trimpot Function
SENSOR TYPE
LOAD TYPE
LIMA
TRIMPOT
LIMB
TRIMPOT
Thermistor
Thermoelectric
Cool Current
Limit
Heat Current
Limit
100 Ω Platinum
RTD, LM335,
AD590
Thermoelectric
Heat Current
Limit
Cool Current
Limit
Thermistor
Resistive Heater
Turn Fully
CCW
Heat Current
Limit
100 Ω Platinum
RTD, LM335,
AD590
Resistive Heater
Heat Current
Limit
Turn Fully
CCW
!
!
