LM20BIM7/NOPB National Semiconductor, LM20BIM7/NOPB Datasheet - Page 6

• Manufacturer Part Number: LM20BIM7/NOPB
• Description: IC, TEMPERATURE SENSOR, ± 1.5°C, SC-70-5
• Manufacturer: National Semiconductor

Specifications of LM20BIM7/NOPB

• Ic Output Type: Voltage
• Sensing Accuracy Range: ± 1.5°C
• Supply Current: 4.5µA
• Supply Voltage Range: 2.4V To 5.5V
• Sensor Case Style: SC-70
• No. Of Pins: 5
• Msl: MSL 1 - Unlimited
• Temperature Sensing Range: -55°C To +130°C
• Rohs Compliant: Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

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2.0 Mounting
The LM20 can be applied easily in the same way as other
integrated-circuit temperature sensors. It can be glued or ce-
mented to a surface. The temperature that the LM20 is sens-
ing will be within about +0.02°C of the surface temperature to
which the LM20'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 temper-
ature between the surface temperature and the air tempera-
ture.
To ensure good thermal conductivity the backside of the
LM20 die is directly attached to the pin 2 GND pin. The tem-
pertures of the lands and traces to the other leads of the LM20
will also affect the temperature that is being sensed.
Alternatively, the LM20 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 LM20 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 LM20 or its connections.
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 LM20 the
equation used to calculate the rise in the die temperature is
as follows:
where I
the output. Since the LM20's junction temperature is the ac-
tual temperature being measured care should be taken to
minimize the load current that the LM20 is required to drive.
The tables shown in
perature of the LM20 without any loading, and the thermal
resistance for different conditions.
See
Still air
Moving air
Still air
Moving air
T
Figure 1
J
FIGURE 3. Temperature Rise of LM20 Due to
= T
Q
Self-Heating and Thermal Resistance (θ
is the quiescent current and I
A
+ θ
for PCB layout samples.
(°C/W)
(°C/W)
JA
TBD
412
312
340
θ
θ
no heat sink
no heat sink
[(V
JA
JA
micro SMD
SC70-5
Figure 3
+
I
Q
) + (V
T
T
J
J
0.17
0.18
TBD
(°C)
(°C)
0.2
− T
− T
summarize the rise in die tem-
+
− V
A
A
O
) I
L
L
(°C/W)
(°C/W)
is the load current on
]
TBD
TBD
small heat sink
350
266
θ
θ
small heat fin
JA
JA
micro SMD
SC70-5
JA
) is the pa-
JA
T
T
J
J
0.19
0.15
TBD
TBD
(°C)
(°C)
)
− T
− T
A
A
6
3.0 Capacitive Loads
The LM20 handles capacitive loading well. Without any pre-
cautions, the LM20 can drive any capacitive load less than
300 pF as shown in
range the LM20 has a maximum output impedance of 160
Ω. In an extremely noisy environment it may be necessary to
add some filtering to minimize noise pickup. It is recommend-
ed that 0.1 μF be added from V
supply voltage, as shown in
it may even be necessary to add a capacitor from the output
to ground with a series resistor as shown in
output capacitor with the 160 Ω maximum output impedance
and a 200 Ω series resistor will form a 442 Hz lowpass filter.
Since the thermal time constant of the LM20 is much slower,
the overall response time of the LM20 will not be significantly
affected.
FIGURE 4. LM20 No Decoupling Required for Capacitive
Capacitive Loading greater than 300 pF. Either placement
FIGURE 5. LM20 with Filter for Noisy Environment and
of resistor as shown above is just as effective.
R (Ω)
200
470
680
1 k
Loads Less than 300 pF.
Figure
4. Over the specified temperature
Figure
+
to GND to bypass the power
5. In a noisy environment
C (µF)
0.001
0.01
0.1
1
Figure
5. A 1 μF
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10090815
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