ORDERING GUIDE
Max Cal Max Error Max Nonlinearity Package
Model Error @ +25
8
C –25
8
C to +105
8
C –25
8
C to +105
8
C Option
AD592CN 0.5°C 1.0°C 0.35°C TO-92
AD592BN 1.0°C 2.0°C 0.4°C TO-92
AD592AN 2.5°C 3.5°C 0.5°C TO-92
AD592–SPECIFICATIONS
AD592AN AD592BN AD592CN
Model Min Typ Max Min Typ Max Min Typ Max Units
ACCURACY
Calibration Error @ +25°C
1
1.5 2.5 0.7 1.0 0.3 0.5 °C
T
A
= 0°C to +70°C
Error over Temperature 1.8 3.0 0.8 1.5 0.4 0.8 °C
Nonlinearity
2
0.15 0.35 0.1 0.25 0.05 0.15 °C
T
A
= –25°C to +105°C
Error over Temperature
3
2.0 3.5 0.9 2.0 0.5 1.0 °C
Nonlinearity
2
0.25 0.5 0.2 0.4 0.1 0.35 °C
OUTPUT CHARACTERISTICS
Nominal Current Output
@ +25°C (298.2K) 298.2 298.2 298.2 µA
Temperature Coefficient 1 1 1 µA/°C
Repeatability
4
0.1 0.1 0.1 °C
Long Term Stability
5
0.1 0.1 0.1 °C/month
ABSOLUTE MAXIMUM RATINGS
Operating Temperature –25 +105 –25 +105 –25 +105 °C
Package Temperature
6
–45 +125 –45 +125 –45 +125 °C
Forward Voltage (+ to –) 44 44 44 V
Reverse Voltage (– to +) 20 20 20 V
Lead Temperature
(Soldering 10 sec) 300 300 300 °C
POWER SUPPLY
Operating Voltage Range 4 30 4 30 4 30 V
Power Supply Rejection
+4 V < V
S
< +5 V 0.5 0.5 0.5 °C/V
+5 V < V
S
< +15 V 0.2 0.2 0.2 °C/V
+15 V < V
S
< +30 V 0.1 0.1 0.1 °C/V
NOTES
1
An external calibration trim can be used to zero the error @ +25°C.
2
Defined as the maximum deviation from a mathematically best fit line.
3
Parameter tested on all production units at +105°C only. C grade at –25°C also.
4
Maximum deviation between +25°C readings after a temperature cycle between –45°C and +125°C. Errors of this type are noncumulative.
5
Operation @ +125°C, error over time is noncumulative.
6
Although performance is not specified beyond the operating temperature range, temperature excursions within the package temperature range will not damage the device.
Specifications subject to change without notice.
Specifications shown in boldface are tested on all production units at final electrical test. Results from those tests are used to calculate outgoing quality levels. All min
and max specifications are guaranteed, although only those shown in boldface are tested on all production units.
(typical @ T
A
= +258C, V
S
= +5 V, unless otherwise noted)
TEMPERATURE SCALE CONVERSION EQUATIONSMETALIZATION DIAGRAM
66MILS
42MILS
V+
V–
REV. A
–2–
°R = °F +459.7
K = °C +273.15
8C =
5
9
(8F –32)
8F =
9
5
8C +32
Typical Performance Curves–AD592
Typical @ VS = +5 V
TOTAL ERROR –
o
C
TEMPERATURE –
o
C
–25 0 +25 +70 +105
+2.0
+1.5
+1.0
+0.5
0
–0.5
–1.0
–1.5
–2.0
AD592CN Accuracy Over Temperature
+2.0
+1.5
+1.0
+0.5
0
–0.5
–1.0
–1.5
–2.0 –25 0 +25 +70 +105
TEMPERATURE –
o
C
TOTAL ERROR –
o
C
AD592AN Accuracy Over Temperature
TOTAL ERROR –
o
C
TEMPERATURE –
o
C
–25 0 +25 +70 +105
+2.0
+1.5
+1.0
+0.5
0
–0.5
–1.0
–1.5
–2.0
AD592BN Accuracy Over Temperature
0.75
0.50
0.25
0
–0.25
–0.50
–0.75 0 500 1000 1500 2000
TIME – Hours
TOTAL ERROR –
o
C
Long-Term Stability @ +85
°
C and 85% Relative Humidity
REV. A –3–
0.75
0.50
0.25
0
–0.25
–0.50
–0.75 0 500 1000 1500 2000
TIME – Hours
TOTAL ERROR –
o
C
Long-Term Stability @ +125
°
C
AD592
REV. A
–4–
THEORY OF OPERATION
The AD592 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, Boltzman’s constant and q, the
charge of an electron are constant, the resulting voltage is
directly Proportional To Absolute Temperature (PTAT). In the
AD592 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 +25°C and the
temperature extremes is shown in Figure 1.
SUPPLY VOLTAGE – Volts
378
248
061
I
OUT
– µA
2345
298
+105
o
C
+25
o
C
–25
o
C
UP TO
30V
Figure 1. V-I Characteristics
Factory trimming of the scale factor to 1 µA/K is accomplished
at the wafer level by adjusting the AD592’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 5 V supply. The device is then packaged
and automatically temperature tested to specification.
FACTORS AFFECTING AD592 SYSTEM PRECISION
The accuracy limits given on the Specifications page for the
AD592 make it easy to apply in a variety of diverse applications.
To calculate a total error budget in a given system it is impor-
tant to correctly interpret the accuracy specifications, non-
linearity errors, the response of the circuit to supply voltage
variations and the effect of the surrounding thermal environ-
ment. As with other electronic designs external component se-
lection will have a major effect on accuracy.
CALIBRATION ERROR, ABSOLUTE ACCURACY AND
NONLINEARITY SPECIFICATIONS
Three primary limits of error are given for the AD592 such that
the correct grade for any given application can easily be chosen
for the overall level of accuracy required. They are the calibra-
tion accuracy at +25°C, and the error over temperature from
0°C to +70°C and –25°C to +105°C. These specifications cor-
respond to the actual error the user would see if the current out-
put of an AD592 were converted to a voltage with a precision
resistor. Note that the maximum error at room temperature,
over the commercial IC temperature range, or an extended
range including the boiling point of water, can be directly read
from the specifications table. All three error limits are a combi-
nation of initial error, scale factor variation and nonlinearity de-
viation from the ideal 1 µA/K output. Figure 2 graphically
depicts the guaranteed limits of accuracy for an AD592CN.
TEMPERATURE – oC
+1.0
+0.5
–25 +1050 +25 +70
0
–0.5
–1.0
TOTAL ERROR – oC
MAXIMUM ERROR
OVER TEMPERATURE
TYPICAL ERROR
CALIBRATION
ERROR LIMIT
MAXIMUM ERROR
OVER TEMPERATURE
Figure 2. Error Specifications (AD592CN)
The AD592 has a highly linear output in comparison to older
technology sensors (i.e., thermistors, RTDs and thermo-
couples), thus a nonlinearity error specification is separated
from the absolute accuracy given over temperature. As a maxi-
mum deviation from a best-fit straight line this specification rep-
resents the only error which cannot be trimmed out. Figure 3 is
a plot of typical AD592CN nonlinearity over the full rated tem-
perature range.
TYPICAL NONLINEARITY
+0.2
+0.1
–25 +1050 +25 +70
0
–0.1
–0.2
TEMPERATURE – oC
NONLINEARITY – oC
Figure 3. Nonlinearity Error (AD592CN)
TRIMMING FOR HIGHER ACCURACY
Calibration error at 25°C can be removed with a single tempera-
ture trim. Figure 4 shows how to adjust the AD592’s scale fac-
tor in the basic voltage output circuit.
AD592
REV. A –5–
+V
AD592
R
100Ω
950Ω
VOUT = 1mV/K
Figure 4. Basic Voltage Output (Single Temperature Trim)
To trim the circuit the temperature must be measured by a ref-
erence sensor and the value of R should be adjusted so the out-
put (V
OUT
) corresponds to 1 mV/K. Note that the trim
procedure should be implemented as close as possible to the
temperature highest accuracy is desired for. In most applications
if a single temperature trim is desired it can be implemented
where the AD592 current-to-output voltage conversion takes
place (e.g., output resistor, offset to an op amp). Figure 5 illus-
trates the effect on total error when using this technique.
AFTER SINGLE
TEMPERATURE
CALIBRATION
ACCURACY
WITHOUT TRIM
+1.0
+0.5
–25 +105+25
0
–0.5
–1.0
TEMPERATURE –
o
C
TOTAL ERROR –
o
C
Figure 5. Effect of Scale Factor Trim on Accuracy
If greater accuracy is desired, initial calibration and scale factor
errors can be removed by using the AD592 in the circuit of
Figure 6.
8.66kΩ
R1
1kΩ
97.6kΩ
R2
5kΩ
7.87kΩ
AD741
V
OUT
= 100mV/
o
C
+5V
AD1403
V–
AD592
Figure 6. 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 range being trimmed for is
nonlinearity. A typical plot of two trim accuracy is given in
Figure 7.
SUPPLY VOLTAGE AND THERMAL ENVIRONMENT
EFFECTS
The power supply rejection characteristics of the AD592 mini-
mizes 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 AD592 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 –
o
C
TOTAL ERROR –
o
C
0 +75
Figure 7. Typical Two Trim Accuracy
The thermal environment in which the AD592 is used deter-
mines two performance traits: the effect of self-heating on accu-
racy 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 vari-
ables; the power consumption level of the circuit and the
thermal resistance between the chip and the ambient environ-
ment (θ
JA
). Self-heating error in °C can be derived by multiply-
ing the power dissipation by θ
JA
. Because errors of this type can
vary widely for surroundings with different heat sinking capaci-
ties it is necessary to specify θ
JA
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
common clip-on heat sink will reduce the error by 25% or more
in critical high temperature, large supply voltage situations.
Table I. Thermal Characteristics
Medium θ
JA
(°C/watt) τ (sec)*
Still Air
Without Heat Sink 175 60
With Heat Sink 130 55
Moving Air
Without Heat Sink 60 12
With Heat Sink 40 10
Fluorinert Liquid 35 5
Aluminum Block** 30 2.4
NOTES
*τ is an average of five time constants (99.3% of final value). In cases where the
thermal response is not a simple exponential function, the actual thermal re-
sponse may be better than indicated.
**With thermal grease.
AD592
REV. A
–6–
V
T
AVG
(1mV/K)
AD592
+5V
333.3Ω
(0.1%)
V
T
AVG
(10mV/K)
10kΩ
(0.1%)
+15V
AD592
AD592
AD592
Figure 9. Average and Minimum Temperature
Connections
The circuit of Figure 10 demonstrates a method in which a
voltage output can be derived in a differential temperature
measurement.
R1
50kΩ
10kΩ
AD741
V
OUT
= (T
1
– T
2
) x
(10mV/
o
C)
10kΩ
5MΩ
–V
+V
AD592
AD592
Figure 10. 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 magni-
tude of V+ and V– is not the same, the difference in power con-
sumption between the two devices can cause a differential
self-heating error.
Cold junction compensation (CJC) used in thermocouple signal
conditioning can be implemented using an AD592 in the circuit
configuration of Figure 11. Expensive simulated ice baths or
hard to trim, inaccurate bridge circuits are no longer required.
AD OP07E
REFERENCE
JUNCTION
100kΩ
10kΩ
V
OUT
+7.5V
MEASURING
JUNCTION
1kΩ
AD592
R
THERMOCOUPLE
TYPE APPROX.
R VALUE
J
K
T
E
S
R
52Ω
41Ω
41Ω
61Ω
6Ω
6Ω
2.5V
AD1403
R
G1
R
G2
(1kΩ)
Cu
Cu
Figure 11. Thermocouple Cold Junction Compensation
Response of the AD592 output to abrupt changes in ambient
temperature can be modeled by a single time constant
τ
expo-
nential function. Figure 8 shows typical response time plots for
several media of interest.
PERCENT OF FINAL TEMPERATURE
TIME – sec
100
80
60
50
40
30
20
10
90
70
ABCD
E
F
0 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300
A ALUMINUM BLOCK
B FLUORINERT LIQUID
C MOVING AIR (WITH HEAT SINK)
D MOVING AIR (WITHOUT HEAT SINK)
E STILL AIR (WITH HEAT SINK)
F STILL AIR (WITHOUT HEAT SINK)
Figure 8. Thermal Response Curves
The time constant, τ, is dependent on θ
JA
and the thermal ca-
pacities 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 where ne-
glected in the analysis, however, they will sink or conduct heat
directly through the AD592’s solder dipped Kovar leads. When
faster response is required a thermally conductive grease or glue
between the AD592 and the surface temperature being mea-
sured should be used. In free air applications a clip-on heat sink
will decrease output stabilization time by 10-20%.
MOUNTING CONSIDERATIONS
If the AD592 is thermally attached and properly protected, it
can be used in any temperature measuring situation where the
maximum range of temperatures encountered is between –25°C
and +105°C. Because plastic IC packaging technology is em-
ployed, excessive mechanical stress must be safeguarded against
when fastening the device with a clamp or screw-on heat tab.
Thermally conductive epoxy or glue is recommended under
typical mounting conditions. In wet or corrosive environments,
any electrically isolated metal or ceramic well can be used to
shield the AD592. Condensation at cold temperatures can cause
leakage current related errors and should be avoided by sealing
the device in nonconductive epoxy paint or dips.
APPLICATIONS
Connecting several AD592 devices in parallel adds the currents
through them and produces a reading proportional to the aver-
age temperature. Series AD592s will indicate the lowest tem-
perature because the coldest device limits the series current
flowing through the sensors. Both of these circuits are depicted
in Figure 9.
AD592
REV. A –7–
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 AD592 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
G1
and R
G2
for the desired noninverting
gain. The offset adjustment shown simply references the AD592
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 AD592 offers a noise immune current output, it is
not compatible with process control/industrial automation cur-
rent loop standards. Figure 12 is an example of a temperature to
4–20 mA transmitter for use with 40 V, 1 kΩ systems.
In this circuit the 1 µA/K output of the AD592 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 AD592 may be chosen.
AD592
AD581
35.7kΩ
10mV/oC
10kΩ12.7kΩ5kΩ500Ω
+20V
–20V
VT
10Ω
C
RT
5kΩ
1mA/oC
208
17°C ≈ 4mA
33°C ≈ 20µA
Figure 12. Temperature to 4–20 mA Current Transmitter
Reading temperature with an AD592 in a microprocessor based
system can be implemented with the circuit shown in Figure 13.
AD1403
950Ω
9kΩ
1kΩ
100Ω
+5V
AD592
SPAN
TRIM CENTER
POINT
TRIM
FORMAT
BPO/UPO
200Ω
µP CONTROL
GND
V
IN HI
V
I HI
N
V
I LO
N
V
I LO
N
8 BITS
OUT
AD670
ADCPORT
R/W CS CE
V
CC
Figure 13. 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 130°C span the AD592 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 AD592 in the circuit of Figure 14.
AD592
10kΩ
R
HYST
R
PULL-UP
+15V
COMPARATOR
(OPTIONAL)
C
R
HIGH
62.7kΩ
R
SET
10kΩ
C
TEMP > SETPOINT
OUTPUT HIGH
TEMP < SETPOINT
OUTPUT LOW
R
LOW
27.3kΩ
AD581
Figure 14. Variable Temperature Thermostat
R
HIGH
and R
LOW
determine the limits of temperature controlled
by the potentiometer R
SET
. The circuit shown operates over the
full temperature range (–25°C to +105°C) the AD592 is rated
for. The reference maintains a constant set point voltage and
insures that approximately 7 V appears across the sensor. If it is
necessary to guardband for extraneous noise hysteresis can be
added by tying a resistor from the output to the ungrounded
end of R
LOW.
Multiple remote temperatures can be measured using several
AD592s with a CMOS multiplexer or a series of 5 V logic gates
because of the device’s current-mode output and supply-voltage
compliance range. The on-resistance of a FET switch or output
impedance of a gate will not affect the accuracy, as long as 4 V
is maintained across the transducer. MUXs and logic driving
circuits should be chosen to minimize leakage current related
errors. Figure 15 illustrates a locally controlled MUX switching
the signal current from several remote AD592s. CMOS or TTL
gates can also be used to switch the AD592 supply voltages,
with the multiplexed signal being transmitted over a single
twisted pair to the load.
AD7501
D
E
C
O
D
E
R
/
D
R
I
V
E
R
T
8
T
2
T
1
REMOTE
AD592s S1
S2
S8
E
N
TTL DTL TO
CMOS I/O
CHANNEL
SELECT
+15V –15V
V
OUT
10kΩ
Figure 15. Remote Temperature Multiplexing
AD592
REV. A
–8–
To minimize the number of MUXs required when a large num-
ber of AD592s are being used, the circuit can be configured in a
matrix. That is, a decoder can be used to switch the supply volt-
age to a column of AD592s while a MUX is used to control
which row of sensors are being measured. The maximum num-
ber of AD592s which can be used is the product of the number
of channels of the decoder and MUX.
An example circuit controlling 80 AD592s is shown in Figure
16. A 7-bit digital word is all that is required to select one of
the sensors. The enable input of the multiplexer turns all the
sensors off for minimum dissipation while idling.
+15V
COLUMN
SELECT
4028 BCD TO DECIMAL DECODER ROW
SELECT
E
N
+15V
–15V
80 – AD592s
10kΩ
V
OUT
AD7501
8-CHANNEL MUX
Figure 16. Matrix Multiplexer
To convert the AD592 output to °C or °F a single inexpensive
reference and op amp can be used as shown in Figure 17. Al-
though this circuit is similar to the two temperature trim circuit
shown in Figure 6, two important differences exist. First, the
gain resistor is fixed alleviating the need for an elevated tem-
perature trim. Acceptable accuracy can be achieved by choosing
an inexpensive resistor with the correct tolerance. Second, the
AD592 calibration error can be trimmed out at a known conve-
nient temperature (i.e., room temperature) with a single pot ad-
justment. This step is independent of the gain selection.
R
R
OFFSET
/R
GAIN
AD741
V
OUT
= 100mV/(
o
C OR
o
F)
+5V
AD1403
V–
o
C
o
F≈ 9.1kΩ
≈ 9.8kΩ100kΩ
180kΩ
R
GAIN
R
OFFSET
AD592
R
CAL
2.5V
R
GAIN
R
OFFSET
Figure 17. Celsius or Fahrenheit Thermometer
PRINTED IN U.S.A. C819b–2–7/93
OUTLINE DIMENSIONS
Dimensions shown in inches and (mm).
0.105 (2.66)
0.080 (2.42)
0.105 (2.66)
0.080 (2.42)
0.165 (4.19)
0.125 (3.94)
SQUARE
0.019 (0.482)
0.016 (0.407)
0.105 (2.66)
0.095 (2.42)
0.055 (1.39)
0.045 (1.15)
SEATING
PLANE
0.500
(12.70)
MIN
0.205 (5.20)
0.175 (4.96)
0.210 (5.33)
0.170 (4.32)
123
BOTTOM VIEW
0.135
(3.43)
MIN
0.050
(1.27)
MAX
