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參數(shù)資料
| 型號： | LM50B |
| 文件頁數(shù)： | 4/8頁 |
| 文件大?。?/td> | 174K |
| 代理商： | LM50B |
1.0 Mounting
The LM50 can be applied easily in the same way as other
integrated-circuit temperature sensors. It can be glued or
cemented to a surface and its temperature will be within
about 0.2
§
C of the surface temperature.
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 of the LM50 die would be at an inter-
mediate temperature between the surface temperature and
the air temperature.
To ensure good thermal conductivity the backside of the
LM50 die is directly attached to the GND pin. The lands and
traces to the LM50 will, of course, be part of the printed
circuit board, which is the object whose temperature is be-
ing measured. These printed circuit board lands and traces
will not cause the LM50s temperature to deviate from the
desired temperature.
Alternatively, the LM50 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 LM50 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
condensation can occur. Printed-circuit coatings and var-
nishes such as Humiseal and epoxy paints or dips are often
used to ensure that moisture cannot corrode the LM50 or its
connections.
Temperature Rise of LM50 Due to Self-Heating
(Thermal Resistance,
i
JA
)
SOT-23
**
no heat sink
Still air
450
C/W
Moving air
*
Heat sink used is
(/2
×
square printed circuit board with 2 oz. foil with part
attached as shown in Figure 2.
**
Part soldered to 30 gauge wire.
SOT-23
small heat fin
*
260
C/W
180
§
C/W
2.0 Capacitive Loads
TL/H/12030–7
FIGURE 3. LM50 No Decoupling Required
for Capacitive Load
TL/H/12030–8
FIGURE 4. LM50C with Filter for Noisy Environment
The LM50 handles capacitive loading very well. Without any
special precautions, the LM50 can drive any capacitive load.
The LM50 has a nominal 2 k
X
output impedance (as can be
seen in the block diagram). The temperature coefficient of
the output resistors is around 1300 ppm/
§
C. Taking into ac-
count this temperature coefficient and the initial tolerance of
the resistors the output impedance of the LM50 will not ex-
ceed 4 k
X
. In an extremely noisy environment it may be
necessary to add some filtering to minimize noise pickup. It
is recommended that 0.1
m
F be added from V
IN
to GND to
bypass the power supply voltage, as shown inFigure 4. In a
noisy environment it may be necessary to add a capacitor
from the output to ground. A 1
m
F output capacitor with the
4 k
X
output impedance will form a 40 Hz lowpass filter.
Since the thermal time constant of the LM50 is much slower
than the 25 ms time constant formed by the RC, the overall
response time of the LM50 will not be significantly affected.
For much larger capacitors this additional time lag will in-
crease the overall response time of the LM50.
TL/H/12030–17
*
R2
&
2k with a typical 1300 ppm/
§
C drift.
FIGURE 5. Block Diagram
http://www.national.com
4
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| LM50BIM3 | 制造商:Texas Instruments 功能描述:TEMPERATURE SENSOR SMD SOT-23-3 |
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