LM61BIM3 National Semiconductor, LM61BIM3 Datasheet - Page 6

• Manufacturer Part Number: LM61BIM3
• Description: TEMPERATURE SENSOR
• Manufacturer: National Semiconductor

Specifications of LM61BIM3

• Peak Reflow Compatible (260 C): No
• Ic Function: Temperature Sensor IC
• Leaded Process Compatible: No
• Mounting Type: Surface Mount
• Package / Case: 3-SOT-23
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

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1.0 Mounting
The LM61 can be applied easily in the same way as other
integrated-circuit temperature sensors. It can be glued or
cemented to a surface. The temperature that the LM61 is
sensing will be within about +0.2˚C of the surface tempera-
ture that LM61’s leads are attached to.
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 measured would be at an intermediate
temperature between the surface temperature and the air
temperature.
To ensure good thermal conductivity the backside of the
LM61 die is directly attached to the GND pin. The lands and
traces to the LM61 will, of course, be part of the printed
circuit board, which is the object whose temperature is being
measured.
Alternatively, the LM61 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 LM61 and
*Part soldered to 30 gauge wire.
**Heat sink used is
***Part glued and leads soldered to 1" square of 1/16" printed circuit board with 2oz. foil or similar.
2.0 Capacitive Loads
The LM61 handles capacitive loading well. Without any spe-
cial precautions, the LM61 can drive any capacitive load as
shown in Figure 4. Over the specified temperature range the
LM61 has a maximum output impedance of 5 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
supply voltage, as shown in Figure 5. In a noisy environment
it may be necessary to add a capacitor from the output to
ground. A 1 µF output capacitor with the 5 kΩ maximum
output impedance will form a 32 Hz lowpass filter. Since the
thermal time constant of the LM61 is much slower than the 5
ms time constant formed by the RC, the overall response
time of the LM61 will not be significantly affected. For much
larger capacitors this additional time lag will increase the
overall response time of the LM61.
FIGURE 4. LM61 No Decoupling Required for
Still air
Moving air
1
⁄
2
Capacitive Load
" square printed circuit board with 2 oz. foil with part attached as shown in Figure 2.
(˚C/W)
450
θ
S
no heat sink
JA
to GND to bypass the power
SOT-23*
T
FIGURE 3. Temperature Rise of LM61 Due to
J
0.26
(˚C)
Self-Heating and Thermal Resistance (θ
− T
A
(˚C/W)
260
180
θ
small heat fin
01289715
JA
SOT-23**
T
6
J
0.13
0.09
(˚C)
− T
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 LM61 or its connec-
tions.
The thermal resistance junction to ambient (θ
rameter used to calculate the rise of a device junction tem-
perature due to its power dissipation. For the LM61 the
equation used to calculate the rise in the die temperature is
as follows:
where I
the output. Since the LM61’s junction temperature is the
actual temperature being measured care should be taken to
minimize the load current that the LM61 is required to drive.
The table shown in Figure 3 summarizes the rise in die
temperature of the LM61 without any loading with a 3.3V
supply, and the thermal resistance for different conditions.
A
FIGURE 5. LM61 with Filter for Noisy Environment
T
J
Q
(˚C/W)
= T
180
θ
is the quiescent current and I
90
no heat sink
JA
A
+ θ
TO-92*
JA
JA
)
[(+V
T
J
0.09
0.05
(˚C)
− T
S
I
Q
A
) + (+V
(˚C/W)
140
θ
small heat fin
70
S
JA
− V
TO-92***
L
is the load current on
O
) I
L
T
]
J
0.07
0.03
(˚C)
JA
− T
) is the pa-
A
01289716