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TMP17F

Low Cost, Current Output Temperature Transducer

Analog Devices 

TMP17

+5V

TMP17

333.3Ω

(0.1%)

VTAVG (1mV/K)

+15V

TMP17

TMP17

TMP17

10kΩ

(0.1%)

VTAVG (10mV/K)

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.

+V

TMP17

R1

TMP17 50kΩ

5MΩ

10kΩ

10kΩ

OP196

VOUT = (T1 – T2) x

(10mV/oC)

–V

Figure 14. Differential Measurements

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

devices. By increasing the gain resistor (10 kΩ) temperature

measurements can be made with higher resolution. If the

magnitude of Vϩ and VϪ 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.

MEASURING

JUNCTION

+7.5V

2.5V

REF43

10kΩ

Cu

1kΩ

TMP17

REFERENCE

Cu JUNCTION

100kΩ

THERMOCOUPLE

TYPE

J

K

T

E

S

R

APPROX.

R VALUE

52Ω

41Ω

41Ω

61Ω

6Ω

6Ω

OP193

VOUT

RG2

(1kΩ)

RG1

R

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 RG1 and RG2 for the desired noninverting

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 kΩ 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.

REF01E

TMP17

35.7kΩ

10mV/ C RT

5kΩ

17 C ≈ 4mA

33 C ≈ 20µA

1mA/ C

+20V

OP97

C

10kΩ 12.7kΩ

5kΩ 500Ω

10Ω

VT

–20V

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.

+5V

REF43

2.5V

ROFFSET

R

RCAL

ROFFSET/RGAIN

RGAIN

OP196

ROFFSET

C ≈ 9.1kΩ

F ≈ 9.8kΩ

RGAIN

100kΩ

180kΩ

VOUT = 100mV/( C OR F)

TMP17

V–

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.

–6–

REV. 0

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