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參數(shù)資料
| 型號： | LM27CIM5-ZHJ |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 溫度/濕度傳感器 |
| 英文描述： | SOT-23, 【3∑C Accurate, 120∑C-150∑C Factory Preset Thermostat |
| 中文描述： | DIGITAL TEMP SENSOR-SINGLE TRIP POINT, 3Cel, RECTANGULAR, SURFACE MOUNT |
| 封裝： | PLASTIC, SOT-23, 5 PIN |
| 文件頁數(shù)： | 6/10頁 |
| 文件大?。?/td> | 584K |
| 代理商： | LM27CIM5-ZHJ |
Applications Hints
(Continued)
TABLE 1. Resistive compensation for capacitive
loading of V
TEMP
C
LOAD
≤
100pF
1nF
10nF
100nF
≥
1μF
R (
)
0
8200
3000
1000
430
NOISE CONSIDERATIONS
The LM27 has excellent power supply noise rejection. Listed
below is a variety of signals used to test the LM27 power
supply rejection. False triggering of the output was not ob-
served when these signals where coupled into the V+ pin of
the LM27.
square wave 400kHz, 1Vp-p
square wave 2kHz, 200mVp-p
sine wave 100Hz to 1MHz, 200mVp-p
Testing was done while maintaining the temperature of the
LM27 one degree centigrade way from the trip point with the
output not activated.
MOUNTING CONSIDERATIONS
The LM27 can be applied easily in the same way as other
integrated-circuit temperature sensors. It can be glued or
cemented to a surface. The temperature that the LM27 is
sensing will be within about +0.06C of the surface tempera-
ture to which the LM27’s leads are attached to.
This presumes that the ambient air temperature is almost the
same as the surface temperature; if the air temperature were
much higher or lower than the surface temperature, the
actual temperature measured would be at an intermediate
temperature between the surface temperature and the air
temperature.
To ensure good thermal conductivity, the backside of the
LM27 die is directly attached to the GND pin (pin 2). The
temperatures of the lands and traces to the other leads of the
LM27 will also affect the temperature that is being sensed.
Alternatively, the LM27 can be mounted inside a sealed-end
metal tube, and can then be dipped into a bath or screwed
into a threaded hole in a tank. As with any IC, the LM27 and
accompanying wiring and circuits must be kept insulated and
dry, to avoid leakage and corrosion. This is especially true if
the circuit may operate at cold temperatures where conden-
sation can occur. Printed-circuit coatings and varnishes such
as Humiseal and epoxy paints or dips are often used to
ensure that moisture cannot corrode the LM27 or its connec-
tions.
The junction to ambient thermal resistance (
θ
JA
) is the pa-
rameter used to calculate the rise of a part’s junction tem-
perature due to its power dissipation. For the LM27 the
equation used to calculate the rise in the die junction tem-
perature is as follows:
(3)
where T
A
is the ambient temperature, V
+
is the power supply
voltage, I
Q
is the quiescent current, I
L_TEMP
is the load
current on the V
TEMP
output, V
DO
is the voltage on the digital
output, and I
is the load current on the digital output. Since
the LM27’s junction temperature is the actual temperature
being measured, care should be taken to minimize the load
current that the LM27 is required to drive.
The tables shown in
Figure 3
summarize the thermal resis-
tance for different conditions and the rise in die temperature
of the LM27 without any loading on V
and a 10k pull-up
resistor on an open-drain digital output with a 5.5V power
supply.
20030717
a) R in series with capacitor
20030718
b) R in series with signal path
FIGURE 2. Resistor placement for capacitive loading
compensation of V
TEMP
SOT23-5
no heat sink
θ
JA
(C/W)
250
TBD
SOT23-5
small heat sink
θ
JA
(C/W)
TBD
TBD
T
J
T
A
(C)
0.11
TBD
T
J
T
A
(C)
TBD
TBD
Still Air
Moving Air
FIGURE 3. Thermal resistance (
θ
) and temperature
rise due to self heating (T
J
T
A
)
L
www.national.com
6
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