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TMP17FSZ
Low Cost, Current Output Temperature Transducer
REV. A
Low Cost, Current Outputemperature Transducer
FEATURES
Operating Temperature Range: –40�C to +105�C
Single-Supply Operation: 4 V to 30 V
Excellent Repeatability and Stability
High Level Output: 1 �A/K
Monolithic IC: Temperature In/Current Out
Minimal Self-Heating Errors
APPLICATIONS
Appliance Temperature Sensor
Automotive Temperature Measurement and Control
HVAC System Monitoring
Industrial Temperature Control
Thermocouple Cold Junction Compensation
GENERAL DESCRIPTIONThe TMP17 is a monolithic integrated circuit temperature trans-
ducer that provides an output current proportional to absolute
temperature. For a wide range of supply voltages, the transducer
acts as a high impedance temperature dependent current source
of 1 µA/K. Improved design and laser wafer trimming of the
IC’s thin-film resistors allow the TMP17 to achieve absolute
accuracy levels and nonlinearity errors previously unattainable
at a comparable price.
The TMP17 can be employed in applications from –40�C to
+105�C where conventional temperature sensors (i.e., thermistor,
RTD, thermocouple, diode) are currently being used. Expensive
linearization circuitry, precision voltage references, bridge
components, resistance measuring circuitry, and cold junction
compensation are not required with the TMP17.
The TMP17 is available in a low cost SOIC-8 surface-mount
package.
PRODUCT HIGHLIGHTSA wide operating temperature range (–40�C to +105�C) and
highly linear output make the TMP17 an ideal substitute for
older, more limited sensor technologies (i.e., thermistors, RTDs,
diodes, thermocouples).The TMP17 is electrically rugged; supply irregularities and
variations or reverse voltages up to 20 V will not damage
thedevice.Because the TMP17 is a temperature dependent current
source, it is immune to voltage noise pickup and IR drops in
the signal leads when used remotely.
*. Patent No. 4,123,698
FUNCTIONAL BLOCK DIAGRAM
PACKAGE DIAGRAM
SOIC-8The high output impedance of the TMP17 provides greater
than 0.5�C/V rejection of supply voltage drift and ripple.Laser wafer trimming and temperature testing ensures that
TMP17 units are easily interchangeable.Initial system accuracy will not degrade significantly over time.
The TMP17 has proven long term performance and repeat-
ability advantages inherent in integrated circuit design and
construction.
Figure 1.Transfer Characteristic
(VS = 5.0 V, –40�C ≤ TA ≤ 105�C, unless otherwise noted.)OUTPUT
POWER SUPPLY
NOTESAn external calibration trim can be used to zero the error @ 25�C.Defined as the maximum deviation from a mathematically best fit line.Maximum deviation between 25�C readings after a temperature cycle between –40�C and +105�C. Errors of this type are noncumulative.Operation at 150�C. Errors of this type are noncumulative.
Specifications subject to change without notice.
ABSOLUTE MAXIMUM RATINGS*Maximum Supply Voltage . . . . . . . . . . . . . . . . . . . . . . . . .30 V
Operating Temperature Range . . . . . . . . . . .–40�C to +105�C
Maximum Forward Voltage (1 to 2) . . . . . . . . . . . . . . . . .44 V
Maximum Reverse Voltage (2 to 1) . . . . . . . . . . . . . . . . . .20 V
Dice Junction Temperature . . . . . . . . . . . . . . . . . . . . . .175�C
Storage Temperature Range . . . . . . . . . . . . .–65�C to +160�C
Lead Temperature (Soldering, 10 sec) . . . . . . . . . . . . .300�C
*Stresses above those listed under Absolute Maximum Ratings may cause perma-
nent damage to the device. This is a stress rating only and functional operation at
or above this specification is not implied. Exposure to the above maximum rating
conditions for extended periods may affect device reliability.
TEMPERATURE SCALE CONVERSION EQUATIONS
METALLIZATION DIAGRAM
CAUTIONESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000V readily
TMP17F/G–SPECIFICATIONS
ORDERING GUIDE
TPC 1.Accuracy vs. Temperature
TPC 2.Thermal Response in Stirred Oil Bath
TPC 3.Thermal Time Constant in Forced Air
TPC 4.V-I Characteristics
TPC 5.Output Turn-On Settling Time
TMP17
THEORY OF OPERATIONThe TMP17 uses a fundamental property of silicon transistors
to realize its temperature proportional output. If two identical
transistors are operated at a constant ratio of collector current
densities, r, then the difference in base-emitter voltages will be
(kT/q)(ln r). Since both k, Boltzmann’s constant, and q, the
charge of an electron, are constant, the resulting voltage is
directly Proportional to Absolute Temperature (PTAT). In the
TMP17, this difference voltage is converted to a PTAT current
by low temperature coefficient thin film resistors. This PTAT
current is then used to force the total output current to be pro-
portional to degrees Kelvin. The result is a current source with
an output equal to a scale factor times the temperature (K) of
the sensor. A typical V-I plot of the circuit at 125�C and the
temperature extremes is shown in TPC 4.
Factory trimming of the scale factor to 1µA/K is accomplished at
the wafer level by adjusting the TMP17’s temperature reading
so it corresponds to the actual temperature. During laser trim-
ming, the IC is at a temperature within a few degrees of 25�C
and is powered by a 5V supply. The device is then packaged and
automatically temperature tested to specification.
FACTORS AFFECTING TMP17 SYSTEM PRECISIONThe accuracy limits in the Specifications table make the TMP17
easy to apply in a variety of diverse applications. To calculate a
total error budget in a given system, it is important to correctly
interpret the accuracy specifications, nonlinearity errors, the
response of the circuit to supply voltage variations, and the effect
of the surrounding thermal environment. As with other electronic
designs, external component selection will have a major effect
on accuracy.
CALIBRATION ERROR, ABSOLUTE ACCURACY, AND
NONLINEARITY SPECIFICATIONSTwo primary limits of error are given for the TMP17 such that
the correct grade for any given application can easily be chosen
for the overall level of accuracy required. They are the calibration
accuracy at +25�C and the error over temperature from –40�C
to +105�C. These specifications correspond to the actual error
the user would see if the current output of a TMP17 were
converted to a voltage with a precision resistor. Note that the
maximum error at room temperature or over an extended range,
including the boiling point of water, can be read directly from
the Specifications table. The error limits are a combination of
initial error, scale factor variation, and nonlinearity deviation
from the ideal 1µA/K output. TPC 1 graphically depicts the
guaranteed limits of accuracy for a TMP17GS.
The TMP17 has a highly linear output in comparison to older
technology sensors (i.e., thermistors, RTDs, and thermocouples),
thus a nonlinearity error specification is separated from the
absolute accuracy given over temperature. As a maximum deviation
from a best-fit straight line, this specification represents the only
error that cannot be trimmed out. Figure 2 is a plot of typical
TMP17 nonlinearity over the full rated temperature range.
Figure 2.Nonlinearity Error
TRIMMING FOR HIGHER ACCURACYCalibration error at 25�C can be removed with a single tem-
perature trim. Figure 3 shows how to adjust the TMP17’s scale
factor in the basic voltage output circuit.
Figure 3.Basic Voltage Output (Single Temperature Trim)
To trim the circuit, the temperature must be measured by a refer-
ence sensor and the value of R should be adjusted so the output
(VOUT) corresponds to 1mV/K. Note that the trim procedure
should be implemented as close as possible to the temperature
for which highest accuracy is desired. In most applications, if a
single temperature trim is desired, it can be implemented where
the TMP17 current-to-output voltage conversion takes place
(e.g., output resistor, offset to an op amp). Figure 4 illustrates
the effect on total error when using this technique.
If greater accuracy is desired, initial calibration and scale factor
errors can be removed by using the TMP17 in the circuit of
Figure 5.
TMP17
REF43
+5V
97.6k�
5k�Figure 5.Two Temperature Trim Circuit
With the transducer at 0�C, adjustment of R1 for a 0V output
nulls the initial calibration error and shifts the output from Kto �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.typical plot of two trim accuracy is given in Figure 6.
Figure 6.Typical Two Trim Accuracy
SUPPLY VOLTAGE AND THERMAL ENVIRONMENT
EFFECTSThe power supply rejection characteristics of the TMP17 mini-
mize errors due to voltage irregularity, ripple, and noise. If a
supply is used other than 5V (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 (�JA). Self-heating
error in °C can be derived by multiplying the power dissipation
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 5V 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*� 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 � expo-
nential function. TPC 2 and TPC 3 show typical response time
plots for media of interest.
The time constant, �, is dependent on �JA and on the thermal
capacities of the chip and the package. Table I lists the effective
� (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 CONSIDERATIONSIf 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.
APPLICATIONSConnecting 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.
The circuit in Figure 8 demonstrates a method in which a voltage
output can be derived in a differential temperature measurement.
Figure 8.Differential Measurements
R1 can be used to trim out the inherent offset between the two
devices. By increasing the gain resistor (10kΩ), temperature mea-
surements can be made with higher resolution. If the magnitude
of V1 and V2 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 9. Expensive simulated ice baths or hard
to trim, inaccurate bridge circuits are no longer required.
Figure 9. Thermocouple Cold Junction Compensation
The circuit shown can be optimized for any ambient temperature
range or thermocouple type by simply selecting the correct value
for the scaling resistor R. The TMP17 output (1µA/K) � 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 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 10 is an example of a temperature4–20mA transmitter for use with 40V, 1kΩ systems.
In this circuit the 1µA/K output of the TMP17 is amplified tomA/°C and offset so that 4mA is equivalent to 17°C and 20mA
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.
Figure 10.Temperature to 4–20mA Current Transmitter
Reading temperature with a TMP17 in a microprocessor based
system can be implemented with the circuit shown in Figure 11.
Figure 11.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.
A variable temperature controlling thermostat can easily be built
using the TMP17 in the circuit in Figure 12.
Figure 12.Variable Temperature Thermostat
TMP17
