© 2023
10
WHY5640 TEMPERATURE CONTROLLER
+0.5 V
SENSOR BRIDGE AMPLIFIER
R
S
R
T
1
7
6
THERMISTOR
SETPOINT
TRIMPOT
WHY5640
ERR
AGND
SENS
Figure 8. Thermistor Operation Circuit
Select setpoint resistor, R
S
, equal to the thermistor resistance
at the desired operating temperature.
When the setpoint resistor, R
S
, and thermistor, R
T
, are equal
resistance values, the Sensor Bridge Amplifier is balanced
and the voltage on Pin 6 (ERR) will equal 1 V with reference
to Pin 1 (AGND).
If the setpoint resistor, R
S
, is larger than the thermistor
resistance, R
T
, then the control loop will produce a cooling
current (OUTB) since the temperature sensed by the
thermistor is above (hotter than) the setpoint temperature.
If the setpoint resistor, R
S
, is smaller than the thermistor
resistance, R
T
, then the control loop will produce a heating
current (OUTA) since the temperature sensed by the
thermistor is below (cooler than) the setpoint temperature.
RTDs
illustrates how to connect the WHY5640 for
operation with PTC (Positive Temperature Coefficient) RTD
sensors. Resistors, R
2
, should be chosen large enough to
prevent self heating of the RTD due to the current flowing
through it. Most applications generally only require R
2
to be
double the resistance of the RTD.
+0.5 V
SENSOR BRIDGE AMPLIFIER
R
S
R
RTD
1
7
6
RTD
SETPOINT
TRIMPOT
WHY5640
ERR
AGND
SENS
R
2
R
2
Figure 9. RTD Operation Circuit
Select setpoint resistor, R
S
, equal to the RTD resistance,
R
RTD
, at the desired operating temperature.
When the setpoint resistor, R
S
, and RTD, R
RTD
, are equal
in value, the Sensor Bridge Amplifier is balanced and the
voltage on Pin 6 (ERR) will equal 1 V with reference to Pin 1
(AGND).
If the setpoint resistor, R
S
, is larger than the RTD resistance,
R
RTD
, then the control loop will produce a heating current
since the temperature sensed by the RTD is below (cooler
than) the setpoint temperature.
If the setpoint resistor, R
S
, is smaller than the RTD resistance,
R
RTD
, then the control loop will produce a cooling current
since the temperature sensed by the RTD is above (hotter
than) the setpoint temperature.
LM335s AND AD590s
Operating instructions can be found in the
Technical Information on page 17
TEMPERATURE SENSOR MOUNTING
The temperature sensor should be in good thermal contact
with the device being temperature controlled. This requires
that the temperature sensor be mounted using thermal
epoxy or some form of mechanical mounting and thermal
grease.
Avoid placing the temperature sensor physically far from the
thermoelectric. This is typically the cause for long thermal
lag and creates a sluggish thermal response that produces
considerable temperature overshoot.
STEP 4
Control Loop Proportional Gain &
Integrator Time Constant - Pins 1, 3, 5, & 6
Adjust the control loop parameters by setting the values
of the two resistors and capacitors (R
G
, R
L
, and C
L
; refer
to
). All three components interact to set the
proportional gain and the integrator time constant.
Recommended values for the three components are shown
in
for common sensor and load combinations. A
“fast” load can change temperature quickly; conversely
a “slow” load is slower to respond to temperature change
commands.
Equations for determining the proportional gain and
integrator time constant are also provided in order to tune
the controller to a variety of load conditions not covered in
.
The relationship between the three components is
summarized by the gain-integrator product, k
T
, in
Equation 3
.
