Rainbow Electronics LM50 - Manual (Page 4)

Typical Performance Characteristics
To generate these curves the LM50 was mounted to a printed
circuit board as shown in Figure 2 . (Continued)
1.0 Mounting
The LM50 can be applied easily in the same way as other
integrated-circuit temperature sensors. It can be glued or ce-
mented 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 ac-
tual temperature of the LM50 die would be at an intermediate
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 cir-
cuit 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 en-
sure that moisture cannot corrode the LM50 or its connec-
tions.
Temperature Rise of LM50 Due to Self-Heating
(Thermal Resistance,
θ
JA
)
SOT-23 SOT-23
no heat sink * small heat fin **
Still air 450˚C/W 260˚C/W
Moving air 180˚C/W
* Part soldered to 30 gauge wire.
** Heat sink used is 1 ⁄ 2 " square printed circuit board with 2 oz. foil with part at-
tached 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 k
Ω 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
Ω . In an extremely noisy environment it may be nec-
essary to add some filtering to minimize noise pickup. It is
recommended that 0.1 µF be added from V
IN
to GND to by-
Supply Voltage
vs Supply Current
DS012030-30
Start-Up Response
DS012030-31
DS012030-19
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
DS012030-7
FIGURE 3. LM50 No Decoupling Required
for Capacitive Load
DS012030-8
FIGURE 4. LM50C with Filter for Noisy Environment
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