tmp17gs-reel Analog Devices, Inc., tmp17gs-reel Datasheet - Page 5

• Manufacturer Part Number: tmp17gs-reel
• Description: Low Cost, Current Output Temperature Transducer
• Manufacturer: Analog Devices, Inc.

If greater accuracy is desired, initial calibration and scale factor
errors can be removed by using the TMP17 in the circuit of
Figure 5.
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 range being trimmed for is nonlinearity.
A typical plot of two trim accuracy is given in Figure 6.
SUPPLY VOLTAGE AND THERMAL ENVIRONMENT
EFFECTS
The power supply rejection characteristics of the TMP17 mini-
mize 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.
The thermal environment in which the TMP17 is used determines
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 temperature 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 environment (
error in °C can be derived by multiplying the power dissipation
by
with different heat sinking capacities, it is necessary to specify
REV. A
JA
. Because errors of this type can vary widely for surroundings
–0.1
–0.2
–0.3
REF43
0.2
0.1
0
Figure 5. Two Temperature Trim Circuit
–40
Figure 6. Typical Two Trim Accuracy
+5V
–25
8.66k
7.87k
TMP17
0
1k
R1
TEMPERATURE – C
–
+
V–
25
97.6k
OP196
5k
R2
V
OUT
75
= 100mV/ C
+
–
JA
). Self-heating
105
JA
–5–
under several conditions. 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.
Medium
Still Air
Moving Air @ 500 FPM
Fluorinert Liquid
* is an average of one time constant (63.2% of final value). In cases where the
Response of the TMP17 output to abrupt changes in ambient
temperature can be modeled by a single time constant expo-
nential function. TPC 2 and TPC 3 show typical response time
plots for media of interest.
The time constant, , is dependent on
capacities of the chip and the package. Table I lists the effective
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 maxi-
mum range of temperatures encountered is between –40 C and
+105 C. Thermally conductive epoxy or glue is recommended
under typical mounting conditions. In wet environments, conden-
sation 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. TMP17s connected in series 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 7.
thermal response is not a simple exponential function, the actual thermal
response may be better than indicated.
(time to reach 63.2% of the final value) for several different
+
–
Figure 7. Average and Minimum Temperature
Connections
333.3
(0.1%)
+5V
+
–
Table I. Thermal Characteristics
+
–
V
TMP17
T
AVG
(1mV/1K)
(0.1%)
10k
158
60
35
JA
+15V
+
–
+
–
+
–
JA
( C/W)
TMP17
TMP17
TMP17
and on the thermal
V
T
AVG
TMP17
(10mV/1K)
52
10
2
(sec)*