參數(shù)資料
型號: AD22100KCHIPS
廠商: ANALOG DEVICES INC
元件分類: 溫度/濕度傳感器
英文描述: Voltage Output Temperature Sensor with Signal Conditioning
中文描述: ANALOG TEMP SENSOR-VOLTAGE, 1.93V
封裝: CHIP
文件頁數(shù): 4/6頁
文件大?。?/td> 230K
代理商: AD22100KCHIPS
REV. B
–4–
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 resis-
tor, similar to an RTD, which is built into the IC. Figure 4
shows a simplified block diagram of the AD22100.
V+
V
OUT
Ι
R
T
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 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.
E
°
C
TEMPERATURE –
°
C
4
–4
150
–2
–3
–50
0
–1
1
2
3
100
50
0
MAXIMUM ERROR
OVER TEMPERATURE
TYPICAL ERROR
MAXIMUM ERROR
OVER TEMPERATURE
Figure 5. 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 output stage structure shown in Figure 6.
V
OUT
V+
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
μ
A. (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 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).
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 +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.
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