© 2023
9
WHY5640 TEMPERATURE CONTROLLER
Table 3. Current Limit Set Resistor vs Maximum Output
Current
Maximum
Output
Current
(Amps)
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1.1
1.2
1.3
1.4
1.5
1.6
1.7
1.8
1.9
2.0
2.1
2.2
2.3
Current
Limit Set
Resistor
(kΩ)
R
A
, R
B
1.60
1.69
1.78
1.87
1.97
2.08
2.19
2.31
2.44
2.58
2.72
2.88
3.05
3.23
3.43
3.65
3.88
4.13
4.42
4.72
5.07
5.45
5.88
6.36
shows the circuit for adjustable current limits.
Figure 6. Independently Adjustable Heat and Cool Current
Limits
CCW
1
2
3
AGND
WHY5640
LIMA
LIMB
R
A
R
B
CW
W
CCW
CW
W
1.5 kΩ
1.5 kΩ
5 kΩ
SINGLE TURN
TRIMPOT
5 kΩ
SINGLE TURN
TRIMPOT
STEP 2
Disabling Output Current - Pins 1 - 3
Use a Double Pole-Single Throw (DPST) switch to enable
and disable the output current as shown in
Figure 7. Enable/Disable Output Current Circuit
STEP 3
Sensors - Pins 1, 6, & 7
Use one of the sensors in the sections listed below:
SENSOR SELECTION
Select a temperature sensor that is responsive around the
desired operating temperature. The temperature sensor
should produce a large sensor output for small changes in
temperature. Sensor selection should maximize the voltage
change per ºC for best stability.
Table 4 compares temperature sensors versus their ability to
maintain stable load temperatures with the WHY5640.
Table 4. Temperature Sensor Comparison of voltage change
per degree Celsius
SENSOR
Thermistor
RTD
AD590
LM335
RATING
Best
Poor
Good
Good
Operating instructions for external voltage setpoint using the
previously described sensors can be found in the
Technical Information on page 17
THERMISTOR
Connect a setpoint resistor, R
S
, (or trimpot) across
Pins 1 (AGND) and 7 (SENS). Connect a NTC (Negative
Temperature Coefficient) thermistor, R
T
across Pins 6 (ERR)
and 7 (SENS).
shows the thermistor operation
circuit.
1
2
3
AGND
WHY5640
LIMA
LIMB
R
A
R
B
1.5 kΩ
DISABLE
R
B
-
1.5 kΩ
1.5 kΩ
R
A
-
1.5 kΩ
ENABLE
DPST SWITCH
