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PDF LM20CIM7 Data sheet ( Hoja de datos )
| Número de pieza | LM20CIM7 | |
| Descripción | LM20 2.4V/ 10A/ SC70/ micro SMD Temperature Sensor | |
| Fabricantes | National Semiconductor | |
| Logotipo |  |
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October 1999
LM20
2.4V, 10µA, SC70, micro SMD Temperature Sensor
General Description
The LM20 is a precision analog output CMOS
integrated-circuit temperature sensor that operates over a
−55˚C to +130˚C temperature range. The power supply op-
erating range is +2.4 V to +5.5 V. The transfer function of
LM20 is predominately linear, yet has a slight predictable
parabolic curvature. The accuracy of the LM20 when speci-
fied to a parabolic transfer function is ±1.5˚C at an ambient
temperature of +30˚C. The temperature error increases lin-
early and reaches a maximum of ±2.5˚C at the temperature
range extremes. The temperature range is affected by the
power supply voltage. At a power supply voltage of 2.7 V to
5.5 V the temperature range extremes are +130˚C and
−55˚C. Decreasing the power supply voltage to 2.4 V
changes the negative extreme to −30˚C, while the positive
remains at +130˚C.
The LM20’s quiescent current is less than 10 µA. Therefore,
self-heating is less than 0.02˚C in still air. Shutdown capabil-
ity for the LM20 is intrinsic because its inherent low power
consumption allows it to be powered directly from the output
of many logic gates or does not necessitate shutdown at all.
Applications
n Cellular Phones
n Computers
n Power Supply Modules
n Battery Management
n FAX Machines
n Printers
n HVAC
n Disk Drives
n Appliances
Features
n Rated for full −55˚C to +130˚C range
n Available in an SC70 and a micro SMD package
n Predictable curvature error
n Suitable for remote applications
Key Specifications
n Accuracy at +30˚C
n Accuracy at +130˚C & −55˚C
n Power Supply Voltage Range
n Current Drain
n Nonlinearity
n Output Impedance
n Load Regulation
0 µA < IL< +16 µA
±1.5 to ±4 ˚C (max)
±2.5 to ±5 ˚C (max)
+2.4V to +5.5V
10 µA (max)
±0.4 % (typ)
160 Ω (max)
−2.5 mV (max)
Typical Application
Output Voltage vs Temperature
DS100908-2
VO = (−3.88x10−6xT2) + (−1.15x10−2xT) + 1.8639
or
where:
T is temperature, and VO is the measured output voltage of the LM20.
Full-Range Celsius (Centigrade) Temperature Sensor (−55˚C to +130˚C)
Operating from a Single Li-Ion Battery Cell
DS100908-24
© 1999 National Semiconductor Corporation DS100908
www.national.com
1 page  
1.0 LM20 Transfer Function
The LM20’s transfer function can be described in different
ways with varying levels of precision. A simple linear transfer
function, with good accuracy near 25˚C, is
VO= −11.69 mV/˚C x T + 1.8663 V
Over the full operating temperature range of −55˚C to
+130˚C, best accuracy can be obtained by using the para-
bolic transfer function
VO = (−3.88x10−6xT2) + (−1.15x10−2xT) + 1.8639
solving for T:
A linear transfer function can be used over a limited tempera-
ture range by calculating a slope and offset that give best re-
sults over that range. A linear transfer function can be calcu-
lated from the parabolic transfer function of the LM20. The
slope of the linear transfer function can be calculated using
the following equation:
m = −7.76 x 10−6x 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
Tmin=−30 to Tmax=+100˚C:
T=35˚C
and
m = −11.77 mV/˚C
The offset of the linear transfer function can be calculated
using the following equation:
b = (VOP(Tmax) + VOP(T) + m x (Tmax+T))/2,
where:
• VOP(Tmax) is the calculated output voltage at Tmax using
the parabolic transfer function for VO
• VOP(T) is the calculated output voltage at T using the
parabolic transfer function for VO.
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 lin-
ear transfer function increases with wider temperature
ranges.
Temperature Range
Tmin (˚C)
−55
−40
−30
-40
−10
+35
+20
Tmax (˚C)
+130
+110
+100
+85
+65
+45
+30
Linear Equation
VO=
−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
FIGURE 2. First order equations optimized for different temperature ranges.
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 ac-
tual temperature measured would be at an intermediate tem-
perature between the surface temperature and the air tem-
perature.
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 en-
sure that moisture cannot corrode the LM20 or its connec-
tions.
The thermal resistance junction to ambient (θJA) is the pa-
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:
TJ = TA + θJA [(V+ IQ) + (V+ − VO) IL]
where IQ is the quiescent current and ILis the load current on
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 Figure 3 summarize the rise in die tem-
perature of the LM20 without any loading, and the thermal
resistance for different conditions.
5 www.national.com
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| PDF Descargar | [ Datasheet LM20CIM7.PDF ] | |
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