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參數資料
| 型號： | LM20SITLXEP |
| 廠商： | National Semiconductor Corporation |
| 元件分類： | 溫度/濕度傳感器 |
| 英文描述： | Enhanced Plastic 2.4V, 10uA, SC70, micro SMD Temperature Sensor |
| 中文描述： | 增強塑料2.4V的，為10uA，SC70封裝，微型貼片溫度傳感器 |
| 文件頁數： | 5/9頁 |
| 文件大小： | 250K |
| 代理商： | LM20SITLXEP |
LM20EP Transfer Function
The LM20EP’s transfer function can be described in different
ways with varying levels of precision. A simple linear transfer
function, with good accuracy near 25C, is
V
O
= 11.69 mV/C x T + 1.8663 V
Over the full operating temperature range of 55C to
+130C, best accuracy can be obtained by using the para-
bolic transfer function
V
O
= (3.88x10
6
xT
2
) + (1.15x10
2
xT) + 1.8639
solving for T:
Alinear transfer function can be used over a limited tempera-
ture range by calculating a slope and offset that give best
results over that range. A linear transfer function can be
calculated from the parabolic transfer function of the
LM20EP. The slope of the linear transfer function can be
calculated using the following equation:
m = 7.76 x 10
6
x T 0.0115,
where T is the middle of the temperature range of interest
and m is in V/C. For example for the temperature range of
T
min
=30 to T
max
=+100C:
T=35C
and
m = 11.77 mV/C
The offset of the linear transfer function can be calculated
using the following equation:
b = (V
OP
(T
max
) + V
OP
(T) + m x (T
max
+T))/2
,
where:
V
(T
) is the calculated output voltage at T
max
using
the parabolic transfer function for V
O
V
(T) is the calculated output voltage at T using the
parabolic transfer function for V
O
.
Using this procedure the best fit linear transfer function for
many popular temperature ranges was calculated in
Figure
2
. As shown in
Figure 2
the error that is introduced by the
linear transfer function increases with wider temperature
ranges.
Mounting
The LM20EP 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 LM20EP is
sensing will be within about +0.02C of the surface tempera-
ture to which the LM20EP’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
LM20EP die is directly attached to the pin 2 GND pin. The
tempertures of the lands and traces to the other leads of the
LM20EP will also affect the temperature that is being
sensed.
Alternatively, the LM20EP 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
LM20EP 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 condensation 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
LM20EP or its connections.
The thermal resistance junction to ambient (
θ
JA
) is the pa-
rameter used to calculate the rise of a device junction tem-
perature due to its power dissipation. For the LM20EP the
equation used to calculate the rise in the die temperature is
as follows:
T
J
= T
A
+
θ
JA
[(V
+
I
Q
) + (V
+
V
O
) I
L
]
where I
is the quiescent current and I
is the load current on
the output. Since the LM20EP’s junction temperature is the
actual temperature being measured care should be taken to
minimize the load current that the LM20EP is required to
drive.
The tables shown in
Figure 3
summarize the rise in die
temperature of the LM20EP without any loading, and the
thermal resistance for different conditions.
Temperature Range
T
min
(C)
55
40
30
-40
10
+35
+20
Linear Equation
V
O
=
11.79 mV/C x T + 1.8528 V
11.77 mV/C x T + 1.8577 V
11.77 mV/C x T + 1.8605 V
11.67 mV/C x T + 1.8583 V
11.71 mV/C x T + 1.8641 V
11.81 mV/C x T + 1.8701 V
11.69 mV/C x T + 1.8663 V
Maximum Deviation of Linear Equation
from Parabolic Equation (C)
±
1.41
±
0.93
±
0.70
±
0.65
±
0.23
±
0.004
±
0.004
T
max
(C)
+130
+110
+100
+85
+65
+45
+30
FIGURE 2. First order equations optimized for different temperature ranges.
L
www.national.com
5
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