Voltage Output Temperature Sensor
a
FEATURES
200°C Temperature Span
Accuracy Better than 62% of Full Scale
Linearity Better than 61% of Full Scale
Temperature Coefficient of 22.5 mV/8C
Output Proportional to Temperature 3 V+
Single Supply Operation
Reverse Voltage Protection
Minimal Self Heating
High Level, Low Impedance Output
APPLICATIONS
HVAC Systems
System Temperature Compensation
Board Level Temperature Sensing
Electronic Thermostats
MARKETS
Industrial Process Control
Instrumentation
Automotive
with Signal Conditioning
AD22100*
SIMPLIFIED BLOCK DIAGRAM
V+
Ι
R
T
V
OUT
GENERAL DESCRIPTION
The AD22100 is a monolithic temperature sensor with on-chip
signal conditioning. It can be operated over the temperature
range –50°C to +150°C, making it ideal for use in numerous
HVAC, instrumentation and automotive applications.
The signal conditioning eliminates the need for any trimming,
buffering or linearization circuitry, greatly simplifying the system
design and reducing the overall system cost.
The output voltage is proportional to the temperature times the
supply voltage (ratiometric). The output swings from 0.25V at
–50°C to +4.75 V at +150°C using a single +5.0V supply.
Due to its ratiometric nature, the AD22100 offers a cost effective solution when interfacing to an analog-to-digital converter.
This is accomplished by using the ADC’s +5V power supply as
a reference to both the ADC and the AD22100 (See Figure 1),
eliminating the need for and cost of a precision reference.
*
Protected by U.S. Patent Nos. 5030849 and 5243319
.
AD22100
–50°C TO +150°C
+5V
REFERENCE
SIGNAL OUTPUT
DIRECT TO ADC
V
O
1kΩ
Figure 1. Application Circuit
0.1µF
INPUT
ANALOG TO
DIGITAL
CONVERTER
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.
© Analog Devices, Inc., 1994
One Technology Way, P.O. Box 9106, Norwood. MA 02062-9106, U.S.A.
Tel: 617/329-4700 Fax: 617/326-8703
AD22100
AD22100–SPECIFICATIONS
(TA = +25°C and V+ = +4 V to +6 V unless otherwise noted)
AD22100K AD22100A AD22100S
Parameter Min Typ Max Min Typ Max Min Typ Max Units
TRANSFER FUNCTION V
= (V+/5 V) × [1.375 V + (22.5 mV/°C) × TA]V
OUT
TEMPERATURE COEFFICIENT (V+/5 V) × 22.5 mV/°C
TOTAL ERROR
Initial Error
T
= +25°C ±0.5 ±2.0 ±1.0 ±2.0 ±1.0 ±2.0 °C
A
Error over Temperature
T
A = TMIN
T
A = TMAX
±0.75 ±2.0 ±2.0 ±3.7 ±3.0 ±4.0 °C
±0.75 ±2.0 ±2.0 ±3.0 ±3.0 ±4.0 °C
Nonlinearity
TA = T
MIN to TMAX
0.5 0.5 1.0 % FS
OUTPUT CHARACTERISTICS
Nominal Output Voltage
V+ = 5.0 V, T
V+ = 5.0 V, T
V+ = 5.0 V, T
V+ = 5.0 V, T
V+ = 5.0 V, T
= 0°C 1.375 V
A
= +100°C 3.625 V
A
= –40°C 0.475 V
A
= +85°C 3.288 V
A
= –50°C 0.250 V
A
V+ = 5.0 V, TA = +150°C 4.750 V
POWER SUPPLY
Operating Voltage +4.0 +5.0 +6.0 +4.0 +5.0 +6.0 +4.0 +5.0 +6.0 V
Quiescent Current 500 650 500 650 500 650 µA
TEMPERATURE RANGE
Guaranteed Temperature Range 0 +100 –40 +85 –50 +150 °C
Operating Temperature Range –50 +150 –50 +150 –50 +150 °C
1
PACKAGE TO-92 TO-92 TO-92
SOIC SOIC SOIC
Specifications subject to change without notice.
CHIP SPECIFICATIONS
(TA = +25°C and V+ = +5.0 V unless otherwise noted)
Parameter Min Typ Max Units
TRANSFER FUNCTION V
= (V+/5 V) × [1.375 + 22.5 mV/°C × TA]V
OUT
TEMPERATURE COEFFICIENT (V+/5V) × 22.5 mV/°C
OUTPUT CHARACTERISTICS
Error
T
= +25°C ±0.5 ±2.0 °C
A
Nominal Output Voltage
TA = +25°C 1.938 V
POWER SUPPLY
Operating Voltage +4.0 +5.0 +6.0 V
Quiescent Current 500 650 µA
TEMPERATURE RANGE
Guaranteed Temperature Range 25 °C
Operating Temperature Range –50 +150 °C
NOTES
1
FS (Full Scale) is defined as that of the operating temperature range, –50°C to +150°C. The listed max specification limit applies to the guaranteed temperature
range. For example, the AD22100K has a nonlinearity of (0.5%) × (200°C) = 1 °C over the guaranteed temperature range of 0°C to +100°C.
Specifications subject to change without notice.
–2–
–2–
REV. B
REV. B
AD22100
WARNING!
ESD SENSITIVE DEVICE
50
12000
100
150
200
800400
FLOW RATE – CFM
θ
JA
– °C/W
(SOIC)
250
(T0-92)
ABSOLUTE MAXIMUM RATINGS
1
Supply Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . +10 V
Reversed Continuous Supply Voltage . . . . . . . . . . . . . . –10 V
Operating Temperature . . . . . . . . . . . . . . . . –50°C to +150°C
Storage Temperature . . . . . . . . . . . . . . . . . . –65°C to +160°C
Output Short Circuit to V+ or Ground . . . . . . . . . . Indefinite
Lead Temperature (Soldering, 10 sec) . . . . . . . . . . . . . +300°C
1
Stresses above those listed under “Absolute Maximum Ratings” may cause
permanent damage to the device. This is a stress rating only; the functional
operation of the device at these or any other conditions above those indicated in the
operation sections of this specification is not implied. Exposure to absolute
maximum rating conditions for extended periods may affect device reliability.
ORDERING GUIDE
Guaranteed
Temperature Package Package
Model/Grade Range Description* Option
AD22100 KT 0°C to 100°C TO-92 TO-92
AD22100 KR 0°C to 100°C SOIC SO-8
AD22100 AT –40°C to +85°C TO-92 TO-92
AD22100 AR –40°C to +85°C SOIC SO-8
AD22100 ST –50°C to +150°C TO-92 TO-92
AD22100 SR –50°C to +150°C SOIC SO-8
AD22100KChips +25°C N/A N/A
*Minimum purchase quantities of 100 pieces for all chip orders.
PIN DESCRIPTION
Mnemonic Function
V+ Power Supply Input
V
O
Device Output
GND Ground Pin must be connected to 0 V.
NC No Connect
PIN CONFIGURATIONS
TO-92
BOTTOM VIEW
(Not to Scale)
PIN 2 PIN 1
PIN 3
GND V
V+
O
SOIC
1
V+
V
2
O
3
NC
(Not to Scale)
GND
4
NC = NO CONNECT
AD22100
TOP VIEW
8
NC
7
NC
6
NC
5
NC
CAUTION
ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily
accumulate on the human body and test equipment and can discharge without detection.
Although the AD22100 features proprietary ESD protection circuitry, permanent damage may
occur on devices subjected to high energy electrostatic discharges. Therefore, proper ESD
precautions are recommended to avoid performance degradation or loss of functionality.
Typical Performance Curves
16
14
12
T (T0-92)
8
6
T (SOIC)
4
2
0
FLOW RATE – CFM
800400
Figure 2. Thermal Response vs. Flow Rate
1200
Figure 3. Thermal Resistance vs. Flow Rate
10
– Sec
τ
REV. B
–3–
AD22100
THEORY OF OPERATION
The AD22100 is a ratiometric temperature sensor IC whose
output voltage is proportional to power supply voltage. The
heart of the sensor is a proprietary temperature-dependent resistor, similar to an RTD, which is built into the IC. Figure 4
shows a simplified block diagram of the AD22100.
V+
Ι
V
OUT
R
T
Figure 4. Simplified Block Diagram
The temperature-dependent resistor, labeled RT, exhibits a
change in resistance that is nearly linearly proportional to temperature. This resistor is excited with a current source that is
proportional to power supply voltage. The resulting voltage
across R
is therefore both supply voltage proportional and lin-
T
early varying with temperature. The remainder of the AD22100
consists of an op amp signal conditioning block that takes the
voltage across R
and applies the proper gain and offset to
T
achieve the following output voltage function:
V
= (V+/5 V) × [1.375 V + (22.5 mV/°C) × TA]
OUT
ABSOLUTE ACCURACY AND NONLINEARITY SPECIFICATIONS
Figure 5 graphically depicts the guaranteed limits of accuracy
for the AD22100 and shows the performance of a typical part.
As the output is very linear, the major sources of error are offset,
i.e., error at room temperature, and span error, i.e., deviation
from the theoretical 22.5 mV/°C. Demanding applications can
achieve improved performance by calibrating these offset and
gain errors so that only the residual nonlinearity remains as a
significant source of error.
OUTPUT STAGE CONSIDERATIONS
As previously stated, the AD22100 is a voltage output device. A
basic understanding of the nature of its output stage is useful for
proper application. Note that at the nominal supply voltage of
5.0 V, the output voltage extends from 0.25V at –50°C to
+4.75 V at +150°C. Furthermore, the AD22100 output pin is
capable of withstanding an indefinite short circuit to either
ground or the power supply. These characteristics are provided
by the output stage structure shown in Figure 6.
V+
V
OUT
Ι
Figure 6. Output Stage Structure
The active portion of the output stage is a PNP transistor with
its emitter connected to the V+ supply and collector connected
to the output node. This PNP transistor sources the required
amount of output current. A limited pull-down capability is
provided by a fixed current sink of about –80 µA. (Here,
“fixed” means the current sink is fairly insensitive to either supply voltage or output loading conditions. The current sink capability is a function of temperature, increasing its pull-down
capability at lower temperatures.)
Due to its limited current sinking ability, the AD22100 is incapable of driving loads to the V+ power supply and is instead intended to drive grounded loads. A typical value for short circuit
current limit is 7 mA, so devices can reliably source 1mA or
2 mA. However, for best output voltage accuracy and minimal
internal self-heating, output current should be kept below 1mA.
Loads connected to the V+ power supply should be avoided as
the current sinking capability of the AD22100 is fairly limited.
These considerations are typically not a problem when driving
a microcontroller analog to digital converter input pin (see
MICROPROCESSOR A/D INTERFACE ISSUES).
4
3
2
1
0
ERROR – °C
–1
–2
–3
–4
–50
TYPICAL ERROR
TEMPERATURE – °C
MAXIMUM ERROR
OVER TEMPERATURE
MAXIMUM ERROR
OVER TEMPERATURE
100500
Figure 5. Typical AD22100 Performance
150
RATIOMETRICITY CONSIDERATIONS
The AD22100 will operate with slightly better accuracy than
that listed in the data sheet specifications if the power supply is
held constant. This is because the AD22100’s output voltage
varies with both temperature and supply voltage, with some
errors. The ideal transfer function describing the output
voltage is:
(V+/5 V) × [1.375 V + (22.5 mV/°C) × T
]
A
The ratiometricity error is defined as the percent change away
from the ideal transfer function as the power supply voltage
changes within the operating range of +4V to +6V. For the
AD22100 this error is typically less than 1%. A movement from
the ideal transfer function by 1% at +25°C, with a supply voltage varying from 5.0 V to 5.50 V, results in a 1.94mV change in
output voltage or 0.08°C error. This error term is greater at
higher temperatures because the output (and error term) is directly proportional to temperature. At 150°C, the error in output voltage is 4.75 mV or 0.19°C.
–4–
REV. B
AD22100
100
0
100
30
10
10
20
0
60
40
50
70
80
90
9080706050403020
STILL AIR
TIME – sec
% OF FINAL VALUES
ALUMINUM
BLOCK
MOVING
AIR
For example, with VS = 5.0 V, and TA = +25°C, the nominal
output of the AD22100 will be 1.9375 V. At V
nominal output will be 2.1313 V, an increase of 193.75mV.
A proportionality error of 1% is applied to the 193.75mV,
yielding an error term of 1.9375 mV. This error term translates
to a variation in output voltage of 2.1293 V to 2.3332V. A
1.94 mV error at the output is equivalent to about 0.08°C error
in accuracy.
If we substitute 150°C for 25°C in the above example, then the
error term translates to a variation in output voltage of 5.2203V
to 5.2298 V. A 4.75 mV error at the output is equivalent to
about 0.19°C error in accuracy.
MOUNTING CONSIDERATIONS
If the AD22100 is thermally attached and properly protected, it
can be used in any measuring situation where the maximum
range of temperatures encountered is between –50°C and
+150°C. Because plastic IC packaging technology is employed,
excessive mechanical stress must be avoided when fastening the
device with a clamp or screw-on heat tab. Thermally conductive epoxy or glue is recommended for typical mounting conditions. In wet or corrosive environments, an electrically isolated
metal or ceramic well should be used to shield the AD22100.
Because the part has a voltage output (as opposed to current), it
offers modest immunity to leakage errors, such as those caused
by condensation at low temperatures.
THERMAL ENVIRONMENT EFFECTS
The thermal environment in which the AD22100 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 of the AD22100 and the thermal
resistance between the chip and the ambient environment θ
Self-heating error in °C can be derived by multiplying the power
dissipation by θ
for surroundings with different heat sinking capacities, it is necessary to specify θ
how the magnitude of self-heating error varies relative to the environment. A typical part will dissipate about 2.2mW at room
temperature with a 5 V supply and negligible output loading. In
still air, without a “heat sink,” the table below indicates a θ
190°C/W, yielding a temperature rise of 0.4°C. Thermal rise
will be considerably less in either moving air or with direct
physical connection to a solid (or liquid) body.
Medium θJA (°C/Watt) τ (sec) *
Aluminum Block 60 2
Moving Air**
Without Heat Sink 75 3.5
Still Air
Without Heat Sink 190 15
*The time constant τ is defined as the time to reach 63.2% of the final
**1200 CFM.
REV. B
Because errors of this type can vary widely
JA.
JA
Table I. Thermal Resistance (TO-92)
temperature change.
= 5.50 V, the
S
.
JA
under several conditions. Table I shows
of
JA
Response of the AD22100 output to abrupt changes in ambient
temperature can be modeled by a single time constant
τ
exponential function. Figure 7 shows typical response time plots for
a few media of interest.
Figure 7. Response Time
The time constant τ is dependent on θJA and the thermal
capacities of the chip and the package. Table I lists the effective
τ
(time to reach 63.2% of the final value) for a few different
media. Copper printed circuit board connections were
neglected in the analysis; however, they will sink or conduct
heat directly through the AD22100’s solder plated copper leads.
When faster response is required, a thermally conductive grease
or glue between the AD22100 and the surface temperature
being measured should be used.
MICROPROCESSOR A/D INTERFACE ISSUES
The AD22100 is especially well suited to providing a low cost
temperature measurement capability for microprocessor/
microcontroller based systems. Many inexpensive 8-bit microprocessors now offer an onboard 8-bit ADC capability at a modest cost premium. Total “cost of ownership” then becomes a
function of the voltage reference and analog signal conditioning
necessary to mate the analog sensor with the microprocessor
ADC. The AD22100 can provide an ideal low cost system by
eliminating the need for a precision voltage reference and any
additional active components. The ratiometric nature of the
AD22100 allows the microprocessor to use the same power supply as its ADC reference. Variations of hundreds of millivolts in
the supply voltage have little effect as both the AD22100 and
the ADC use the supply as their reference. The nominal
AD22100 signal range of 0.25 V to 4.75 V (–50°C to +150°C)
makes good use of the input range of a 0V to 5 V ADC. A
single resistor and capacitor are recommended to provide immunity to the high speed charge dump glitches seen at many
microprocessor ADC inputs (see Figure 1).
An 8-bit ADC with a reference of 5 V will have a least significant bit (LSB) size of 5 V/256 = 19.5 mV. This corresponds to
a nominal resolution of about 0.87°C.
–5–
AD22100
4
5
8
1
0.2440 (6.20)
0.2284 (5.80)
0.1574 (4.00)
0.1497 (3.80)
0.1968 (5.00)
0.1890 (4.80)
0.0500 (1.27)
0.0160 (0.41)
0°-8°
× 45°
0.0196 (0.50)
0.0099 (0.25)
0.0098 (0.25)
0.0075 (0.19)
SEATING
PLANE
0.0500
(1.27)
BSC
0.0688 (1.75)
0.0532 (1.35)
0.0192 (0.49)
0.0138 (0.35)
0.0098 (0.25)
0.0040 (0.10)
USE WITH A PRECISION REFERENCE AS THE SUPPLY VOLTAGE
While the ratiometric nature of the AD22100 allows for system
operation without a precision voltage reference, it can still be
used in such systems. Overall system requirements involving
other sensors or signal inputs may dictate the need for a fixed
precision ADC reference. The AD22100 can be converted to
absolute voltage operation by using a precision reference as the
supply voltage. For example, a 5.00 V reference can be used to
power the AD22100 directly. Supply current will typically be
500 µA which is usually within the output capability of the refer-
ence. A large number of AD22100s may require an additional
op amp buffer, as would scaling down a 10.00V reference that
might be found in “instrumentation” ADCs typically operating
from ±15 V supplies.
OUTLINE DIMENSIONS
Dimensions shown in inches and (mm).
TO-92
0.135
(3.43)
MIN
SEATING PLANE
0.500
(12.70)
MIN
0.105 (2.66)
0.095 (2.42)
0.105 (2.66)
0.080 (2.42)
0.205 (5.20)
0.175 (4.96)
0.210 (5.33)
0.170 (4.58)
0.019 (0.482)
0.016 (0.407)
0.055 (1.39)
0.045 (1.15)
0.050
(1.27)
MAX
SQUARE
C1898b–9–12/94
0.105 (2.66)
0.080 (2.42)
0.165 (4.19)
0.125 (3.94)
SO-8 (SOIC)
PRINTED IN U.S.A.
–6–
REV. B
Loading...