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ADT45 Schematic ( PDF Datasheet ) - Analog Devices

Teilenummer ADT45
Beschreibung (ADT45 / ADT50) Temperature Sensors
Hersteller Analog Devices
Logo Analog Devices Logo 




Gesamt 12 Seiten
ADT45 Datasheet, Funktion
a
FEATURES
Low Voltage Operation (2.7 V to 12 V)
Calibrated Directly in ؇C
10 mV/؇C Scale Factor
؎2؇C Accuracy Over Temperature (typ)
؎0.5؇C Linearity (typ)
Stable with Large Capacitive Loads
Specified –40؇C to +125؇C, Operation to +150؇C
Less than 60 mA Quiescent Current
Low Self-Heating
APPLICATIONS
Environmental Control Systems
Thermal Protection
Industrial Process Control
Fire Alarms
Power System Monitors
CPU Thermal Management
GENERAL DESCRIPTION
The ADT45 and ADT50 are low voltage, precision centigrade
temperature sensors. They provide a voltage output that is lin-
early proportional to the Celsius (Centigrade) temperature. The
ADT45/ADT50 do not require any external calibration to pro-
vide typical accuracies of ± 1°C at +25°C and ± 2°C over the
–40°C to +125°C temperature range. The low output imped-
ance of the ADT45/ADT50, linear output and precise calibra-
tion simplify interfacing to temperature control circuitry and
A/D converters. All three devices are intended for single supply
operation from 2.7 V to 12 V maximum. Supply current runs
well below 60 µA providing very low self-heating—less than
0.1°C in still air. The ADT45/ADT50 are functionally and pin
compatible with LM45/LM50 respectively. The ADT45 pro-
vides a 250 mV output at +25°C and reads temperature from
0°C to +100°C. The ADT50 is specified from –40°C to +125°C,
provides a 750 mV output at +25°C and operates to +125°C
from a single 2.7 V supply. Both the ADT45 and ADT50 have
an output scale factor of +10 mV/°C. Operation extends to
+150°C with reduced accuracy for all devices when operating
from a 12 V supply.
The ADT45/ADT50 are available in the low cost 3-lead
SOT-23 surface mount package.
Low Voltage SOT-23
Temperature Sensors
ADT45/ADT50
FUNCTIONAL BLOCK DIAGRAM
+Vs (2.7V to 12V)
ADT45
ADT50
VOUT
PACKAGE TYPES AVAILABLE
SOT-23
+VS 1
TOP VIEW 3 GND
(Not to Scale)
VOUT 2
REV. 0
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 World Wide Web Site: http://www.analog.com
Fax: 781/326-8703
© Analog Devices, Inc., 1997
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ADT45 Datasheet, Funktion
ADT45/ADT50
120
100
80
60
SOT-23 SOLDERED TO 0.338" ؋ 0.307" Cu PCB
V؉ = 2.7V TO 5V, NO LOAD
40
20
0
0 1 2 3 4 5 6 7 8 9 10
TIME – Sec
Figure 14. Thermal Response Time in Stirred Oil Bath
10mV
100
90
1mS
10
0%
TIME/DIVISION
Figure 15. Temperature Sensor Wideband Output Noise
Voltage. Gain = 100, BW = 157 kHz
APPLICATIONS SECTION
Mounting Considerations
If the ADT45/ADT50 temperature sensors are thermally at-
tached and protected, they can be used in any temperature mea-
surement application where the maximum temperature range of
the medium is between –40°C to +125°C. Properly cemented or
glued to the surface of the medium, these sensors will be within
0.01°C of the surface temperature. Caution should be exercised
as any wiring to the device can act as heat pipes, introducing
errors if the surrounding air-surface interface is not isothermal.
Avoiding this condition is easily achieved by dabbing the leads of
the temperature sensor and the hookup wires with a bead of
thermally conductive epoxy. This will ensure that the ADT45/
ADT50 die temperature is not affected by the surrounding air
temperature.
These temperature sensors, as well as any associated circuitry,
should be kept insulated and dry to avoid leakage and corrosion.
In wet or corrosive environments, any electrically isolated metal
or ceramic well can be used to shield the temperature sensors.
Condensation at very cold temperatures can cause errors and
should be avoided by sealing the device using electrically non-
conductive epoxy paints or dips, or any one of many printed
circuit board coatings and varnishes.
Thermal Environment Effects
The thermal environment in which the ADT45/ADT50 sensors
are used determines two important characteristics: self-heating
effects and thermal response time. Illustrated in Figure 17 is
a thermal model of the ADT45/ADT50 temperature sensors,
which is useful in understanding these characteristics.
TJ JC TC CA
PD CCH
CC
+
TA
2400
2200
2000
1800
1600
1400
1200
ADT45/ADT50
1000
800
600
400
200
0
10
100 1k
FREQUENCY – Hz
10k
Figure 16. Voltage Noise Spectral Density vs. Frequency
Figure 17. ADT45/ADT50 Thermal Circuit Model
In the SOT-23 package, the thermal resistance junction-to-case,
θJC, is 180°C/W. The thermal resistance case-to-ambient, θCA, is
the difference between θJA and θJC, and is determined by the
characteristics of the thermal connection. The temperature
sensor’s power dissipation, represented by PD, is the product of
the total voltage across the device and its total supply current
(including any current delivered to the load). The rise in die
temperature above the medium’s ambient temperature is given
by:
( )T J = PD × θJC + θCA +T A
Thus, the die temperature rise of an ADT45 “RT” package
mounted into a socket in still air at 25°C and driven from a
+5 V supply is less than 0.04°C.
The transient response of the ADT45/ADT50 sensors to a step
change in the temperature is determined by the thermal resistances
and the thermal capacities of the die, CCH, and the case, CC. The
thermal capacity of the case, CC, varies with the measurement
medium since it includes anything that is in direct contact with the
package. In all practical cases, the thermal capacity of the case is
the limiting factor in the thermal response time of the sensor and
can be represented by a single-pole RC-time constant response.
–6– REV. 0
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ADT45 pdf, datenblatt
ADT45/ADT50
As a result of this operation, the lifetime of an integrated circuit
is significantly accelerated due to the increase in rates of reac-
tion within the semiconductor material. A well-understood, and
universal, model used by the semiconductor industry is the
Arrhenius model, which relates the change in rates of reaction
to a change in elevated temperatures. From the Arrhenius model,
an acceleration factor can be calculated and applied to the
specified parameter. For example, this acceleration factor can
be used to reduce a temperature sensor’s long-term stability
(e.g., 0.4°C after 1000 hours at TJ = +150°C) to an observed
shift in that parameter at +25°C. For any semiconductor de-
vice, the acceleration factor is expressed as:
F
=

exp 
Ea
k

×

1
T1
1
T 2

where F = Calculated acceleration factor;
Ea = Activation energy in eV = 0.7 eV;
k = Boltzmann’s constant = 8.63 × 10–5 eV/K;
T1 = Test temperature in Kelvin, TJ = +150°C = 423.15K;
and
T 2 = Desired operating temperature in Kelvin,
TJ = +25°C = 298.15K
For example, if the desired operating temperature of an IC is
+25°C and has been subjected to test temperature of +150°C,
the acceleration factor is:
F = 3.23 × 10–4
With this background information, the ADT45/ADT50’s long-
term stability can be mapped to what its equivalent observed
shift would be at TA = +25°C. As quoted in the data sheet, the
long-term stability of these temperature sensors after 1000 hours
at +150°C is 0.4°C. This shift is equivalent to 0.01°C/day at
TJ = +150°C. To determine what the observed shift would be at
TA = +25°C is a matter of applying the acceleration factor calcu-
lated above to this result:
0.01°C/day × 3.23 × 10–4 = 0.003 m°C/day @ +25°C
Thus, if any of the ADT45/ADT50 devices were to be used at
25°C, then the observed shift would be no more than 0.003 m°C
per day, or 0.1 m°C per month. Calculating the observed shift
for any other operating temperature is simply a matter of calcu-
lating a new acceleration factor.
OUTLINE DIMENSIONS
Dimensions shown in inches and (mm).
3-Lead Plastic Surface Mount Package
RT-3 (SOT-23)
0.1200 (3.048)
0.1102 (2.799)
0.0550 (1.397)
3 0.1040 (2.642)
0.0470 (1.194)
1
0.0827 (2.101)
2
PIN 1
0.0236 (0.599)
0.0177 (0.450)
0.0040 (0.102)
0.0005 (0.013)
SEATING
PLANE
0.0807 (2.050)
0.0701 (1.781)
0.0413 (1.049)
0.0374 (0.950)
0.0440 (1.118)
0.0320 (0.813)
0.0210 (0.533)
0.0146 (0.371)
0.0100 (0.254)
0.0050 (0.127)
0.0059 (0.150)
0.0034 (0.086)
0.027 (0.686)
REF
–12–
REV. 0
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