TMP17

REV. 0

–6–

TMP17

AVG

(1mV/K)

TMP17

+5V

333.3

Ω

(0.1%)

AVG

(10mV/K)

10k

Ω

(0.1%)

+15V

TMP17

TMP17

Figure 13. Average and Minimum Temperature

Connections

The circuit of Figure 14 demonstrates a method in which a

voltage output can be derived in a differential temperature

measurement.

R1

50k

Ω

10k

Ω

OP196

10k

Ω

5M

Ω

–V

+V

TMP17

TMP17

Figure 14. Differential Measurements

R1 can be used to trim out the inherent offset between the two

devices. By increasing the gain resistor (10 k

Ω) temperature

measurements can be made with higher resolution. If the

magnitude of V

and V

is not the same, the difference in

power consumption between the two devices can cause a

differential self-heating error.

Cold junction compensation (CJC) used in thermocouple signal

conditioning can be implemented using a TMP17 in the circuit

configuration of Figure 15. Expensive simulated ice baths or

hard to trim, inaccurate bridge circuits are no longer required.

OP193

REFERENCE

JUNCTION

100k

Ω

10k

Ω

+7.5V

MEASURING

JUNCTION

1k

Ω

TMP17

R

THERMOCOUPLE

TYPE

APPROX.

R VALUE

J

K

T

E

S

R

52

Ω

41

Ω

41

Ω

61

Ω

6

Ω

6

Ω

2.5V

REF43

(1k

Ω)

Cu

Cu

Figure 15. Thermocouple Cold Junction Compensation

The circuit shown can be optimized for any ambient tempera-

ture range or thermocouple type by simply selecting the correct

value for the scaling resistor – R. The TMP17 output (1

µA/K)

times R should approximate the line best fit to the thermocouple

curve (slope in V/

°C) over the most likely ambient temperature

range. Additionally, the output sensitivity can be chosen by

selecting the resistors R

gain. The offset adjustment shown simply references the

TMP17 to

°C. Note that the TC’s of the reference and the

resistors are the primary contributors to error. Temperature

rejection of 40 to 1 can be easily achieved using the above

technique.

Although the TMP17 offers a noise immune current output, it

is not compatible with process control/industrial automation

current loop standards. Figure 16 is an example of a tempera-

ture to 4–20 mA transmitter for use with 40 V, 1 k

Ω systems.

In this circuit the 1

µA/K output of the TMP17 is amplified to

1 mA/

°C and offset so that 4 mA is equivalent to 17°C and

20 mA is equivalent to 33

°C. Rt is trimmed for proper reading

at an intermediate reference temperature. With a suitable choice

of resistors, any temperature range within the operating limits of

the TMP17 may be chosen.

TMP17

REF01E

35.7k

Ω

10mV/ C

10k

Ω

12.7k

Ω

5k

Ω

500

Ω

+20V

–20V

10

Ω

C

5k

Ω

1mA/ C

OP97

17 C

≈ 4mA

33 C

≈ 20µA

Figure 16. Temperature to 4–20 mA Current Transmitter

Reading temperature with a TMP17 in a microprocessor based

system can be implemented with the circuit shown in Figure 17.

R

OP196

+5V

REF43

V–

C

F

≈ 9.1kΩ

≈ 9.8kΩ

100k

Ω

180k

Ω

TMP17

2.5V

Figure 17. Temperature to Digital Output

By using a differential input A/D converter and choosing the

current to voltage conversion resistor correctly, any range of

temperatures (up to the 145

°C span the TMP17 is rated for)

centered at any point can be measured using a minimal number

of components. In this configuration the system will resolve up

to 1

°C.