LM50C National Semiconductor, LM50C Datasheet - Page 4

• Manufacturer Part Number: LM50C
• Description: (LM50B / LM50C) SOT-23 Single-Supply Centigrade Temperature Sensor
• Manufacturer: National Semiconductor

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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
attached as shown in Figure 2
R2
Heat sink used is
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Part soldered to 30 gauge wire
Temperature Rise of LM50 Due to Self-Heating
Still air
Moving air
2k with a typical 1300 ppm C drift
(Thermal Resistance
square printed circuit board with 2 oz foil with part
no heat sink
SOT-23
450 C W
small heat fin
JA
260 C W
180 C W
)
SOT-23
FIGURE 5 Block Diagram
4
2 0 Capacitive Loads
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
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
necessary to add some filtering to minimize noise pickup It
is recommended that 0 1 F be added from V
bypass the power supply voltage as shown in Figure 4 In a
noisy environment it may be necessary to add a capacitor
from the output to ground A 1 F output capacitor with the
4 k
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
FIGURE 4 LM50C with Filter for Noisy Environment
output impedance will form a 40 Hz lowpass filter
FIGURE 3 LM50 No Decoupling Required
In an extremely noisy environment it may be
for Capacitive Load
output impedance (as can be
TL H 12030 – 17
IN
TL H 12030 – 7
TL H 12030 – 8
to GND to