TMP17

REV. 0

–5–

ment (

θ

°C can be derived by multiply-

ing the power dissipation by

θ

vary widely for surroundings with different heat sinking capaci-

ties, it is necessary to specify

θ

Table I shows how the magnitude of self-heating error varies

relative to the environment. In typical free air applications at

25

°C with a 5 V supply the magnitude of the error is 0.2°C or

less. A small glued-on heat sink will reduce the temperature

error in high temperature, large supply voltage situations.

Table I. Thermal Characteristics

Medium

θ

τ (sec)*

Still Air

158

52

Moving Air @ 500 FPM

60

10

Fluorinert Liquid

35

2

NOTES

*

τ is an average of one time constant (63.2% of final value). In cases where the

thermal response is not a simple exponential function, the actual thermal

response may be better than indicated.

Response of the TMP17 output to abrupt changes in ambient

temperature can be modeled by a single time constant

τ

exponential function. Figures 3 and 4 show typical response

time plots for media of interest.

The time constant,

τ, is dependent on θ

capacities of the chip and the package. Table I lists the effective

τ (time to reach 63.2% of the final value) for several different

media. Copper printed circuit board connections will sink or

conduct heat directly through the TMP17’s soldered leads.

When faster response is required a thermally conductive grease

or glue between the TMP17 and the surface temperature being

measured should be used.

MOUNTING CONSIDERATIONS

If the TMP17 is thermally attached and properly protected, it

can be used in any temperature measuring situation where the

maximum range of temperatures encountered is between

40

°C

and

105

°C. Thermally conductive epoxy or glue is recom-

mended under typical mounting conditions. In wet environ-

ments condensation at cold temperatures can cause leakage

current related errors and should be avoided by sealing the

device in nonconductive epoxy paint or conformal coating.

APPLICATIONS

Connecting several TMP17 devices in parallel adds the currents

through them and produces a reading proportional to the

average temperature. Series TMP17s will indicate the lowest

temperature because the coldest device limits the series current

flowing through the sensors. Both of these circuits are depicted

in Figure 13.

If greater accuracy is desired, initial calibration and scale factor

errors can be removed by using the TMP17 in the circuit of

Figure 11.

8.66k

Ω

R1

1k

Ω

97.6k

Ω

R2

5k

Ω

7.87k

Ω

OP196

+5V

REF43

V–

TMP17

Figure 11. Two Temperature Trim Circuit

With the transducer at 0

°C adjustment of R1 for a 0 V output

nulls the initial calibration error and shifts the output from K to

°C. Tweaking the gain of the circuit at an elevated temperature

by adjusting R2 trims out scale factor error. The only error

remaining over the temperature by adjusting R2 trims out scale

factor error. The only error remaining over the temperature

range being trimmed for its nonlinearity. A typical plot of two

trim accuracy is given in Figure 12.

SUPPLY VOLTAGE AND THERMAL ENVIRONMENT

EFFECTS

The power supply rejection characteristics of the TMP17

minimize errors due to voltage irregularity, ripple and noise. If a

supply is used other than 5 V (used in factory trimming), the

power supply error can be removed with a single temperature

trim. The PTAT nature of the TMP17 will remain unchanged.

The general insensitivity of the output allows the use of lower

cost unregulated supplies and means that a series resistance of

several hundred ohms (e.g., CMOS multiplexer, meter coil

resistance) will not degrade the overall performance.

2.0

1.0

25

105

25

0

1.0

2.0

TEMPERATURE – C

0

75

40

Figure 12. Typical Two Trim Accuracy

The thermal environment in which the TMP17 is used deter-

mines two performance traits: the effect of self-heating on

accuracy and the response time of the sensor to rapid changes in

temperature. In the first case, a rise in the IC junction tempera-

ture above the ambient temperature is a function of two

variables; the power consumption level of the circuit and the

thermal resistance between the chip and the ambient environ-