LM50BIM3 National Semiconductor, LM50BIM3 Datasheet - Page 6

• Manufacturer Part Number: LM50BIM3
• Description: IC, TEMPERATURE SENSOR, ± 2°C, 3-SOT-23
• Manufacturer: National Semiconductor

Specifications of LM50BIM3

• Ic Output Type: Voltage
• Sensing Accuracy Range: ± 2°C
• Supply Current: 130µA
• Supply Voltage Range: 4.5V To 10V
• Sensor Case Style: SOT-23
• No. Of Pins: 3
• Termination Type: SMD
• Temperature Sensor Function: Temp Sensor
• Output Type: Analog
• Package Type: SOT-23
• Operating Temperature (min): -25C
• Operating Temperature (max): 100C
• Operating Temperature Classification: Commercial
• Operating Supply Voltage (typ): 5/9V
• Operating Supply Voltage (max): 10V
• Filter Terminals: SMD
• Rohs Compliant: No
• Dc: 0424
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

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Printed Circuit Board
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 interme-
diate 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 being
measured. These printed circuit board lands and traces will
not cause the LM50s temperature to deviate from the de-
sired 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 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 LM50 or its connec-
tions.
FIGURE 2. Printed Circuit Board Used
for Heat Sink to Generate All Curves.
1
⁄
2
" Square Printed Circuit Board
with 2 oz. Foil or Similar
01203019
6
* Part soldered to 30 gauge wire.
** Heat sink used is
attached as shown in Figure 2.
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 kΩ output impedance (as can be
seen in the block diagram). The temperature coefficient of
the output resistors is around 1300 ppm/˚C. Taking into
account this temperature coefficient and the initial tolerance
of the resistors the output impedance of the LM50 will not
exceed 4 kΩ. In an extremely noisy environment it may be
necessary to add some filtering to minimize noise pickup. It
is recommended that 0.1 µF 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 µF output capacitor with the
4 kΩ 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.
Still air
Moving air
FIGURE 4. LM50C with Filter for Noisy Environment
Temperature Rise of LM50 Due to Self-Heating
FIGURE 3. LM50 No Decoupling Required
(Thermal Resistance, θ
1
⁄
2
no heat sink*
" square printed circuit board with 2 oz. foil with part
for Capacitive Load
SOT-23
450˚C/W
small heat fin**
JA
)
SOT-23
IN
to GND to
260˚C/W
180˚C/W
01203007
01203008