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參數(shù)資料
| 型號(hào)： | ADT50 |
| 廠商： | Analog Devices, Inc. |
| 元件分類： | 溫度/濕度傳感器 |
| 英文描述： | Low Voltage SOT-23 Temperature Sensors(低壓溫度傳感器) |
| 中文描述： | 低壓SOT - 23封裝溫度傳感器（低壓溫度傳感器） |
| 文件頁(yè)數(shù)： | 7/12頁(yè) |
| 文件大小： | 168K |
| 代理商： | ADT50 |
ADT45/ADT50
–7–
REV. 0
Figures 11 to 13 illustrate the thermal response time of the
ADT 45/ADT 50 sensors under various conditions. T he thermal
time constant of a temperature sensor is defined to be the time
required for the sensor to reach 63.2% of the final value for a
step change in the temperature.
Basic T emperature Sensor Connections
T he circuit in Figure 18 illustrates the basic circuit configura-
tion for the ADT 45/ADT 50 temperature sensors.
0.1
m
F
V
OUT
2.7V < V
S
< 12V
V
S
GND
ADT45/50
Figure 18. Basic Temperature Sensor Circuit Configuration
Note the 0.1
μ
F bypass capacitor on the input. T his capacitor
should be a ceramic type, have very short leads (surface mount
would be preferable), and located as close a physical proximity
to the temperature sensor supply pin as practical. Since these
temperature sensors operate on very little supply current and
could be exposed to very hostile electrical environments, it is
important to minimize the effects of RFI (Radio-Frequency
Interference) on these devices. T he effect of RFI on these tem-
perature sensors in specific and analog ICs in general is mani-
fested as abnormal dc shifts in the output voltage due to the
rectification of the high frequency ambient noise by the IC. In
those cases where the devices are operated in the presence of
high frequency radiated or conducted noise, a large value tanta-
lum capacitor (>2.2
μ
F) placed across the 0.1
μ
F ceramic may
offer additional noise immunity.
Fahrenheit T hermometers
Although the ADT 45/ADT 50 temperature sensors are centi-
grade temperature sensors, a few components can be used to
convert the output voltage and transfer characteristics to read
Fahrenheit temperatures directly. Shown in Figure 19a is an
example of a simple Fahrenheit thermometer using the ADT 45.
T his circuit can be used to sense temperatures from 41
°
F to
257
°
F with an output transfer characteristic of 1 mV/
°
F using
the ADT 45. T his particular approach does not lend itself well to
the ADT 50 because of its inherent 0.5 V output offset. T he
circuit is constructed with an AD589, a 1.23 V voltage refer-
ence, and four resistors whose values are shown in the figure
table. T he scaling of the output resistance levels was to ensure
minimum output loading on the temperature sensors. A general-
ized expression for the circuit’s transfer equation is given by:
V
OUT
=
R
1
R
1
+
R
2
(ADT 45)
+
R
3
R
3
+
R
4
(AD589)
where ADT 45 = Output voltage of the ADT 45 at the measure-
ment temperature, T
M
, and
AD589 = Output voltage of the reference = 1.23 V.
Note that the output voltage of this circuit in not referenced to
the circuit’s common. If this output voltage were to be directly
applied to the input of an ADC, the ADC’s common should be
adjusted accordingly.
ADT45
V
S
V
OUT
GND
0.1
m
F
V
S
AD589
1.23V
R2
R3
R1
R4
+
—
V
OUT
SENSOR
ADT45
TCV
OUT
1mV/
8
F
R1 (k
V
)
45.3
R2 (k
V
)
10
R3 (k
V
)
10
R4 (k
V
)
374
Figure 19a. ADT45 Fahrenheit Thermometers
T he same circuit principles can be applied to the ADT 50, but
because of the ADT 50’s inherent offset, the circuit uses two
fewer resistors as shown in Figure 19b. In this circuit, the out-
put voltage transfer characteristic is 1 mV/
°
F, but is referenced
to the circuit’s common; however, there is a 58 mV (58
°
F)
offset in the output voltage. For example, the output voltage of
the circuit would read 18 mV, if the ADT 50 is placed in –40
°
F
ambient environment, and 315 mV at 257
°
F.
ADT50
V
S
V
OUT
GND
0.1
m
F
V
S
R2
10k
V
R1
45.3k
V
V
OUT
@ 1mV/
8
F =
MEASURED
8
F
V
OUT
@
2
40
8
F = 18mV
V
OUT
@
1
257
8
F = 315mV
+
–
Figure 19b. ADT50 Fahrenheit Thermometer Version 1
At the expense of additional circuitry, the offset produced by the
circuit in Figure 19b can be avoided by using the circuit in
Figure 19c. In this circuit, the output of the ADT 50 is condi-
tioned by a single-supply, micropower op amp, the OP193.
Although the entire circuit operates from a single +3 V supply,
the output voltage of the circuit reads the temperature directly with
a transfer characteristic of 1 mV/
°
F, without offset. T his is accom-
plished through the use of an ADM660, a supply voltage inverter.
The +3 V supply is inverted and applied to the OP193’s V– terminal.
T hus, for a temperature range between –40
°
F and +257
°
F, the
output of the circuit reads –40 mV to +257 mV. A general expres-
sion for the circuit’s transfer equation is given by:
V
OUT
=
R
6
R
5
+
R
6
1
+
R
4
R
3
(
ADT
50)±
R
4
R
3
V
S
2
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