a
FEATURES
200°C Temperature Span
Accuracy Better than
±2%
of Full Scale
Linearity Better than
±1%
of Full Scale
Temperature Coefficient of 22.5 mV/°C
Output Proportional to Temperature
×
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
GENERAL DESCRIPTION
Voltage Output Temperature Sensor
with Signal Conditioning
AD22100*
SIMPLIFIED BLOCK DIAGRAM
V+
Ι
V
OUT
R
T
+5V
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 0.25 V at
–50°C to +4.75 V at +150°C using a single +5.0 V supply.
Due to its ratiometric nature, the AD22100 offers a cost effec-
tive solution when interfacing to an analog-to-digital converter.
This is accomplished by using the ADC’s +5 V 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
V
O
SIGNAL OUTPUT
DIRECT TO ADC
1kΩ
REFERENCE
ANALOG TO
DIGITAL
CONVERTER
INPUT
0.1µF
–50°C TO +150°C
Figure 1. Application Circuit
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–SPECIFICATIONS
(T = +25°C and V+ = +4 V to +6 V unless otherwise noted)
A
Parameter
TRANSFER FUNCTION
TEMPERATURE COEFFICIENT
TOTAL ERROR
Initial Error
T
A
= +25°C
Error over Temperature
T
A
= T
MIN
T
A
= T
MAX
Nonlinearity
T
A
= T
MIN
to T
MAX
OUTPUT CHARACTERISTICS
Nominal Output Voltage
V+ = 5.0 V, T
A
= 0°C
V+ = 5.0 V, T
A
= +100°C
V+ = 5.0 V, T
A
= –40°C
V+ = 5.0 V, T
A
= +85°C
V+ = 5.0 V, T
A
= –50°C
V+ = 5.0 V, T
A
= +150°C
POWER SUPPLY
Operating Voltage
Quiescent Current
TEMPERATURE RANGE
Guaranteed Temperature Range
Operating Temperature Range
PACKAGE
Specifications subject to change without notice.
AD22100K
Min Typ Max
AD22100A
Min
Typ Max
AD22100S
Min
Typ Max
Units
V
mV/°C
V
OUT
= (V+/5 V)
×
[1.375 V + (22.5 mV/°C)
×
T
A
]
(V+/5 V)
×
22.5
±
0.5
±
2.0
±
1.0
±
2.0
±
2.0
±
3.7
±
2.0
±
3.0
0.5
±
1.0
±
2.0
±
3.0
±
4.0
±
3.0
±
4.0
1.0
°C
°C
°C
% FS
1
±
0.75
±
2.0
±
0.75
±
2.0
0.5
1.375
3.625
0.475
3.288
0.250
4.750
+4.0
+5.0
500
+6.0
650
+100
+150
TO-92
SOIC
+4.0
+5.0 +6.0
500 650
+85
+150
TO-92
SOIC
+4.0
+5.0 +6.0
500 650
+150
+150
TO-92
SOIC
V
V
V
V
V
V
V
µA
°C
°C
0
–50
–40
–50
–50
–50
CHIP SPECIFICATIONS
(T = +25°C and V+ = +5.0 V unless otherwise noted)
A
Parameter
TRANSFER FUNCTION
TEMPERATURE COEFFICIENT
OUTPUT CHARACTERISTICS
Error
T
A
= +25°C
Nominal Output Voltage
T
A
= +25°C
POWER SUPPLY
Operating Voltage
Quiescent Current
TEMPERATURE RANGE
Guaranteed Temperature Range
Operating Temperature Range
Min
Typ
Max
Units
V
OUT
= (V+/5 V)
×
[1.375 + 22.5 mV/°C
×
T
A
] V
(V+/5 V)
×
22.5
mV/°C
±
0.5
1.938
+4.0
+5.0
500
25
–50
±
2.0
°C
V
+6.0
650
V
µA
°C
°C
+150
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–
REV. B
AD22100
ABSOLUTE MAXIMUM RATINGS
1
PIN DESCRIPTION
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
Mnemonic
V+
V
O
GND
NC
Function
Power Supply Input
Device Output
Ground Pin must be connected to 0 V.
No Connect
PIN CONFIGURATIONS
TO-92
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
BOTTOM VIEW
(Not to Scale)
PIN 3
PIN 2
PIN 1
Model/Grade
AD22100 KT
AD22100 KR
AD22100 AT
AD22100 AR
AD22100 ST
AD22100 SR
Guaranteed
Temperature
Range
0°C to 100°C
0°C to 100°C
–40°C to +85°C
–40°C to +85°C
Package
Package
Description* Option
TO-92
SOIC
TO-92
SOIC
TO-92
SO-8
TO-92
SO-8
TO-92
SO-8
N/A
GND
V
O
V+
SOIC
V+ 1
V
O
2
NC 3
8 NC
–50°C to +150°C TO-92
–50°C to +150°C SOIC
N/A
AD22100
7 NC
AD22100KChips +25°C
TOP VIEW
6 NC
(Not to Scale)
5 NC
GND 4
NC = NO CONNECT
*Minimum purchase quantities of 100 pieces for all chip orders.
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.
WARNING!
ESD SENSITIVE DEVICE
Typical Performance Curves
16
14
250
200
12
θ
JA
–
°C/W
T (T0-92)
(SOIC)
– Sec
10
8
150
τ
6
4
2
0
400
800
FLOW RATE – CFM
1200
T (SOIC)
100
(T0-92)
50
0
400
800
FLOW RATE – CFM
1200
Figure 2. Thermal Response vs. Flow Rate
Figure 3. Thermal Resistance vs. Flow Rate
REV. B
–3–
AD22100
THEORY OF OPERATION
OUTPUT STAGE CONSIDERATIONS
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 resis-
tor, similar to an RTD, which is built into the IC. Figure 4
shows a simplified block diagram of the AD22100.
V+
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 0.25 V 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+
Ι
V
OUT
R
T
V
OUT
Ι
Figure 4. Simplified Block Diagram
The temperature-dependent resistor, labeled R
T
, exhibits a
change in resistance that is nearly linearly proportional to tem-
perature. This resistor is excited with a current source that is
proportional to power supply voltage. The resulting voltage
across R
T
is therefore both supply voltage proportional and lin-
early varying with temperature. The remainder of the AD22100
consists of an op amp signal conditioning block that takes the
voltage across R
T
and applies the proper gain and offset to
achieve the following output voltage function:
V
OUT
= (V+/5
V)
×
[1.375
V
+ (22.5
mV/°C)
×
T
A
]
ABSOLUTE ACCURACY AND NONLINEARITY
SPECIFICATIONS
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 sup-
ply voltage or output loading conditions. The current sink ca-
pability is a function of temperature, increasing its pull-down
capability at lower temperatures.)
Due to its limited current sinking ability, the AD22100 is inca-
pable of driving loads to the V+ power supply and is instead in-
tended to drive grounded loads. A typical value for short circuit
current limit is 7 mA, so devices can reliably source 1 mA or
2 mA. However, for best output voltage accuracy and minimal
internal self-heating, output current should be kept below 1 mA.
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).
RATIOMETRICITY CONSIDERATIONS
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.
4
3
2
ERROR –
°C
MAXIMUM ERROR
OVER TEMPERATURE
1
0
–1
–2
–3
–4
–50
TYPICAL ERROR
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 +4 V to +6 V. 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 volt-
age varying from 5.0 V to 5.50 V, results in a 1.94 mV change in
output voltage or 0.08°C error. This error term is greater at
higher temperatures because the output (and error term) is di-
rectly proportional to temperature. At 150°C, the error in out-
put voltage is 4.75 mV or 0.19°C.
MAXIMUM ERROR
OVER TEMPERATURE
0
50
TEMPERATURE –
°C
100
150
Figure 5. Typical AD22100 Performance
–4–
REV. B
AD22100
For example, with V
S
= 5.0 V, and T
A
= +25°C, the nominal
output of the AD22100 will be 1.9375 V. At V
S
= 5.50 V, the
nominal output will be 2.1313 V, an increase of 193.75 mV.
A proportionality error of 1% is applied to the 193.75 mV,
yielding an error term of 1.9375 mV. This error term translates
to a variation in output voltage of 2.1293 V to 2.3332 V. 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 5.2203 V
to 5.2298 V. A 4.75 mV error at the output is equivalent to
about 0.19°C error in accuracy.
MOUNTING CONSIDERATIONS
Response of the AD22100 output to abrupt changes in ambient
temperature can be modeled by a single time constant
τ
expo-
nential function. Figure 7 shows typical response time plots for
a few media of interest.
100
90
80
ALUMINUM
BLOCK
MOVING
AIR
% OF FINAL VALUES
70
60
50
40
30
20
10
0
0
10
20
30
40
50
60
TIME – sec
70
80
90
100
STILL AIR
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 conduc-
tive epoxy or glue is recommended for typical mounting condi-
tions. 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
Figure 7. Response Time
The thermal environment in which the AD22100 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 of the AD22100 and the thermal
resistance between the chip and the ambient environment
θ
JA
.
Self-heating error in
°C
can be derived by multiplying the power
dissipation by
θ
JA.
Because errors of this type can vary widely
for surroundings with different heat sinking capacities, it is nec-
essary to specify
θ
JA
under several conditions. Table I shows
how the magnitude of self-heating error varies relative to the en-
vironment. A typical part will dissipate about 2.2 mW 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
JA
of
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.
Table I. Thermal Resistance (TO-92)
The time constant
τ
is dependent on
θ
JA
and the thermal
capacities of the chip and the package. Table I lists the effec-
tive
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
Medium
Aluminum Block
Moving Air**
Without Heat Sink
Still Air
Without Heat Sink
θ
JA
(°C/Watt)
60
75
190
τ
(sec) *
2
3.5
15
The AD22100 is especially well suited to providing a low cost
temperature measurement capability for microprocessor/
microcontroller based systems. Many inexpensive 8-bit micro-
processors now offer an onboard 8-bit ADC capability at a mod-
est 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 sup-
ply 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 0 V to 5 V ADC. A
single resistor and capacitor are recommended to provide im-
munity 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 signifi-
cant bit (LSB) size of 5 V/256 = 19.5 mV. This corresponds to
a nominal resolution of about 0.87°C.
*The time constant
τ
is defined as the time to reach 63.2% of the final
temperature change.
**1200 CFM.
REV. B
–5–
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