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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)： | 9/12頁(yè) |
| 文件大?。?/td> | 168K |
| 代理商： | ADT50 |
ADT45/ADT50
–9–
REV. 0
to indicate that a microprocessor over-temperature condition
has grown tremendously. T he circuit illustrated in Figure 21
demonstrates one way to generate an interrupt using an ADT 45,
a CMP402 analog comparator, and a REF191, a 2 V precision
voltage reference.
T he circuit has been designed to produce a logic HIGH interrupt
signal if the microprocessor temperature exceeds +80
°
C. T his
80
°
C trip point was chosen arbitrarily (final value set by the
microprocessor thermal reference design) and is set using an
R3-R4 voltage divider of the REF191’s output voltage. Since
the output of the ADT 45 is scaled by 10 mV/
°
C, the voltage at
the CMP402’s inverting terminal is set to 0.8 V.
Since temperature is a slowly moving quantity, the possibility
for comparator chatter exists. T o avoid this condition, hysteresis
is used around the comparator. In this application, a hysteresis
of 5
°
C about the trip point was arbitrarily chosen; the ultimate
value for hysteresis should be determined by the end applica-
tion. T he output logic voltage swing of the comparator with R1
and R2 determine the amount of comparator hysteresis. Using a
3.3 V supply, the output logic voltage swing of the CMP402 is
2.6 V; thus, for a hysteresis of +5
°
C (50 mV @ 10 mV/
°
C), R1
is set to 20 k
and R2 is set to 1 M
. An expression for this
circuit’s hysteresis is given by:
Pentium is a trademark of Intel Corporation.
ADT45
REF191
0.1
m
F
V
S
GND
V
OUT
R5
100k
V
3.3V
0.1
m
F
0.1
m
F
0.1
m
F
R1A
10k
V
R1B
10k
V
C
1000pF
1
m
F
+
R4
10k
V
V
REF
R2
1M
V
<80
8
C
>80
8
C
INTERRUPT
R3
16k
V
1/4 CMP402
Figure 21. Pentium Over Temperature Interrupt Generator
V
HYS
=
R
1
R
2
(
V
LOGIC SWING
,
CMP
02
)
Since the likelihood that this circuit would be used in close
proximity to high speed digital circuits, R1 is split into equal
values and a 1000 pF is used to form a low-pass filter on the
output of the ADT 45. Furthermore, to prevent high frequency
noise from contaminating the comparator trip point, a 0.1
μ
F
capacitor is used across R4.
T hermocouple Signal Conditioning with Cold-Junction
Compensation
T he circuit in Figure 22 conditions the output of a T ype K
thermocouple, while providing cold-junction compensation, for
temperatures between 0
°
C and 250
°
C. T he circuit operates
from single +3.3 V to +12 V supplies and has been designed to
produce an output voltage transfer characteristic of 10 mV/
°
C.
A T ype K thermocouple exhibits a Seebeck coefficient of
approximately 41
μ
V/
°
C; therefore, at the cold junction, the
ADT 45 with a temperature coefficient of 10 mV/
°
C is used with
R1 and R2 to introduce an opposing cold-junction tempera-
ture coefficient of –41
μ
V/
°
C. T his prevents the isothermal,
cold-junction connection between the circuit’s PCB tracks and
the thermocouple’s wires from introducing an error in the mea-
sured temperature. T his compensation works extremely well for
ADT45
V
0–2.5V
R6
100k
V
5%
R2*
102
V
R1*
24.9k
V
OP193
CU
CU
R5*
1.21M
V
P1
50k
V
0.1
m
F
R4
4.99k
V
R3
10M
V
5%
3.3V < V
S
< 12V
CHROMEL
+
ALUMEL
–
TYPE K
THERMO
2
COUPLE
0.1
m
F
COLD
JUNCTION
V
S
V
OUT
GND
ISOTHERMAL
BLOCK
0
8
C
#
T
#
250
8
C
NOTE: ALL RESISTORS 1% UNLESS
OTHERWISE NOTED BY *
Figure 22. A Single Supply, Type K Thermocouple Signal Condition Circuit with Cold-J unction Compensation
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