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AD592 Schematic ( PDF Datasheet ) - Analog Devices

Teilenummer AD592
Beschreibung Low Cost / Precision IC Temperature Transducer
Hersteller Analog Devices
Logo Analog Devices Logo 




Gesamt 9 Seiten
AD592 Datasheet, Funktion
a
FEATURES
High Precalibrated Accuracy: 0.5؇C max @ +25؇C
Excellent Linearity: 0.15؇C max (0؇C to +70؇C)
Wide Operating Temperature Range: –25؇C to +105؇C
Single Supply Operation: +4 V to +30 V
Excellent Repeatability and Stability
High Level Output: 1 A/K
Two Terminal Monolithic IC: Temperature In/
Current Out
Minimal Self-Heating Errors
Low Cost, Precision IC
Temperature Transducer
AD592
CONNECTION DIAGRAM
PIN 3 PIN 2 PIN 1
(–)
(NC)
(+)
* PIN 2 CAN BE EITHER ATTACHED OR UNCONNECTED
BOTTOM VIEW
PRODUCT DESCRIPTION
The AD592 is a two terminal monolithic integrated circuit tem-
perature transducer that provides an output current propor-
tional 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 allows the AD592
to achieve absolute accuracy levels and nonlinearity errors previ-
ously unattainable at a comparable price.
The AD592 can be employed in applications between –25°C
and +105°C where conventional temperature sensors (i.e., ther-
mistor, RTD, thermocouple, diode) are currently being used.
The inherent low cost of a monolithic integrated circuit in a
plastic package, combined with a low total parts count in any
given application, make the AD592 the most cost effective tem-
perature transducer currently available. Expensive linearization
circuitry, precision voltage references, bridge components, resis-
tance measuring circuitry and cold junction compensation are
not required with the AD592.
Typical application areas include: appliance temperature sens-
ing, automotive temperature measurement and control, HVAC
(heating/ventilating/air conditioning) system monitoring, indus-
trial temperature control, thermocouple cold junction compen-
sation, board-level electronics temperature diagnostics,
temperature readout options in instrumentation, and tempera-
ture correction circuitry for precision electronics. Particularly
useful in remote sensing applications, the AD592 is immune to
voltage drops and voltage noise over long lines due to its high
impedance current output. AD592s can easily be multiplexed;
the signal current can be switched by a CMOS multiplexer or
the supply voltage can be enabled with a tri-state logic gate.
The AD592 is available in three performance grades: the
AD592AN, AD592BN and AD592CN. All devices are pack-
aged in a plastic TO-92 case rated from –45°C to +125°C. Per-
formance is specified from –25°C to +105°C. AD592 chips are
also available, contact the factory for details.
PRODUCT HIGHLIGHTS
1. With a single supply (4 V to 30 V) the AD592 offers
0.5°C temperature measurement accuracy.
2. A wide operating temperature range (–25°C to +105°C)
and highly linear output make the AD592 an ideal sub-
stitute for older, more limited sensor technologies (i.e.,
thermistors, RTDs, diodes, thermocouples).
3. The AD592 is electrically rugged; supply irregularities
and variations or reverse voltages up to 20 V will not
damage the device.
4. Because the AD592 is a temperature dependent current
source, it is immune to voltage noise pickup and IR
drops in the signal leads when used remotely.
5. The high output impedance of the AD592 provides
greater than 0.5°C/V rejection of supply voltage drift and
ripple.
6. Laser wafer trimming and temperature testing insures
that AD592 units are easily interchangeable.
7. Initial system accuracy will not degrade significantly over
time. The AD592 has proven long term performance
and repeatability advantages inherent in integrated cir-
cuit design and construction.
378
343
1µA/oK
273
248
–45 –25 0
+70 +105 +125
TEMPERATURE – oC
REV. B
Information furnished by Analog Devices is believed to be accurate and
reliable. However, no responsibility is assumed by Analog Devices for its
use, nor for any infringements of patents or other rights of third parties
which may result from its use. No license is granted by implication or
otherwise under any patent or patent rights of Analog Devices.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781/329-4700
Fax: 781/461-3113






AD592 Datasheet, Funktion
AD592
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.
100
A
C
90 B
D
80
E
70
F
60
50
40
30
20
10
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)
0 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300
TIME – sec
Figure 8. Thermal Response Curves
The time constant, τ, is dependent on θJA 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.
+5V
AD592
333.3
(0.1%)
VTAVG (1mV/K)
+15V
AD592
AD592
AD592
10k
(0.1%)
VTAVG (10mV/K)
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.
+V
AD592
AD592
R1
50k
5M
10k
10k
AD741
VOUT = (T1 – T2) x
(10mV/oC)
–V
Figure 10. Differential Measurements
R1 can be used to trim out the inherent offset between the two
devices. By increasing the gain resistor (10 k) 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.
MEASURING
JUNCTION
+7.5V
AD1403
2.5V
10k
Cu 1k
AD592
REFERENCE
Cu JUNCTION
100k
THERMOCOUPLE
TYPE
J
K
T
E
S
R
APPROX.
R VALUE
52
41
41
61
6
6
AD OP07E
VOUT
RG2
(1k)
RG1
R
Figure 11. Thermocouple Cold Junction Compensation
–6– REV. B

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