© 2013
PAGE 7
WTC3293
www.teamwavelength.com
WTC3293-00400-I
CONFIGURING THE EVALUATION BOARD
STEP 5: ATTACHING THE V
DD
AND V
S
POWER SUPPLIES
The V
DD
power supply is used to power the WTC3243 internal control electronics and must be capable
of sourcing 100 mA of 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 LIMA and LIMB current limit settings.
For simple operation tie V
DD
to V
S
using the Power Select Jumper. See Step 1 for location. 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 V
S
power supply allows the output stage to operate at a voltage lower than the 4.5 volts
required by the V
DD
supply or up to the +30 V maximum. Select V
S
approximately 2.5 volts above
the maximum voltage drop across OUTA and OUTB to reduce the power dissipation in the WTC3243
component and minimize your heatsinking requirements.
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 Terminal Block 1, not both.
STEP 6: CONFIGURING THE HEAT AND COOL CURRENT LIMITS
The WTC3293 LIMA and LIMB trimpots independently adjust the heat and cool current limits from zero
to a full 2.2 A.
With the WTC3243 installed and power to V
S
and V
DD
(no load required), set the limits. Rotate LIMA
or LIMB trimpot and monitor the respective voltage at LIMA and LIMB on Terminal Block 3 (TB3). Use
COM as ground reference. NOTE: Unit must be enabled to adjust limit setting.
Use Table 3 to determine polarity of the limits for your sensor and load.
Use Equation 5 to calculate limit value.
LIMA or LIMB is in V.
I
LIM
is desired maximum output current in A.
Table 3 - LIMA and LIMB Current Limit Trimpot Con
fi
guration
Load Type
LIMA Trimpot
Sensor Type
LIMB Trimpot
100
Platinum RTD,
LM335, AD590
Cool Current Limit
Heat Current Limit
Thermoelectric
Thermoelectric
Thermistor
Cool Current Limit
Heat Current Limit
Thermistor
Resistive Heater
Heat Current Limit
Turn Fully CCW
Turn Fully CCW
Heat Current Limit
Resistive Heater
100
Platinum RTD,
LM335, AD590
Equation 5
Calculating LIMA or LIMB from I
LIM
LIM
=
(
0.3 * I
LIM
)
+ 1
