Typical Performance Characteristics
circuit board as shown in
Figure 3.
(Continued)
Supply Voltage
vs Supply Current
To generate these curves the LM45 was mounted to a printed
Start-Up Response
DS011754-33
DS011754-34
DS011754-23
FIGURE 3. Printed Circuit Board Used for Heat Sink to Generate All Curves.
1
⁄
2
" Square Printed Circuit Board with 2 oz. Foil or Similar
Applications
The LM45 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 LM45 die would be at an intermediate
temperature between the surface temperature and the air
temperature.
To ensure good thermal conductivity the backside of the
LM45 die is directly attached to the GND pin. The lands and
traces to the LM45 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 LM45s temperature to deviate from the de-
sired temperature.
Alternatively, the LM45 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 LM45 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
www.national.com
4
as Humiseal and epoxy paints or dips are often used to in-
sure that moisture cannot corrode the LM45 or its connec-
tions.
Temperature Rise of LM45 Due to Self-Heating
(Thermal Resistance)
SOT-23
no heat sink
*
Still air
Moving air
450˚C/W
SOT-23
small heat fin
**
260˚C/W
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 3.
NSC [ NATIONAL SEMICONDUCTOR ]
