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AD22100SRZ-REEL7 View Datasheet(PDF) - Analog Devices

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Description
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AD22100SRZ-REEL7 Datasheet PDF : 12 Pages
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THEORY OF OPERATION
The AD22100 is a ratiometric temperature sensor IC whose
output voltage is proportional to its 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 7
shows a functional block diagram of the AD22100.
V+
VOUT
RT
Figure 7. 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 the power supply voltage. The resulting voltage
across RT is therefore both supply voltage proportional and line-
arly varying with temperature. The remainder of the AD22100
consists of an op amp signal conditioning block that takes the
voltage across RT and applies the proper gain and offset to
achieve the following output voltage function:
VOUT = (V+/5 V) × (1.375 V + 22.5 mV/°C × TA)
ABSOLUTE ACCURACY AND NONLINEARITY
SPECIFICATIONS
Figure 8 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 off-
set, for instance error at room temperature, span error, and de-
viation from the theoretical 22.5 mV/°C. Demanding applica-
tions can achieve improved performance by calibrating these
offset and gain errors so that only the residual nonlinearity re-
mains as a significant source of error.
AD22100
4
3
2
MAXIMUM ERROR
OVER TEMPERATURE
1
0
TYPICAL ERROR
–1
–2
MAXIMUM ERROR
OVER TEMPERATURE
–3
–4
–50
0
50
100
150
TEMPERATURE (°C)
Figure 8. Typical AD22100 Performance
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 0.25 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 out-
put stage structure shown in Figure 9.
V+
VOUT
Figure 9. Output Stage Structure
The active portion of the output stage is a PNP transistor,
with its emitter connected to the V+ supply and its collector
connected to the output node. This PNP transistor sources the
required amount of output current. A limited pull-down capa-
bility is provided by a fixed current sink of about −80 µA, with
the term fixed referring to a current sink that is fairly insensitive
to either supply voltage or output loading conditions. The cur-
rent sink capability is a function of temperature, increasing its
pull-down capability at lower temperatures.
Rev. D | Page 7 of 12
 

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