LM20
2.4V, 10A, SC70, micro SMD Temperature Sensor
General Description
The
LM20
is
a
precision
analog
output
CMOS
integrated-circuit temperature sensor that operates over a
-55C to +130C 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
1.5C at an ambient
temperature of +30C. The temperature error increases lin-
early and reaches a maximum of
2.5C 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 +130C and
-55C. Decreasing the power supply voltage to 2.4 V
changes the negative extreme to -30C, while the positive
remains at +130C.
The LM20's quiescent current is less than 10 A. Therefore,
self-heating is less than 0.02C 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 -55C to +130C 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 +30C
1.5 to
4 C (max)
n
Accuracy at +130C & -55C
2.5 to
5 C (max)
n
Power Supply Voltage Range
+2.4V to +5.5V
n
Current Drain
10 A (max)
n
Nonlinearity
0.4 % (typ)
n
Output Impedance
160
(max)
n
Load Regulation
0 A
<
I
L
<
+16 A
-2.5 mV (max)
Typical Application
DS100908-2
V
O
= (-3.88x10
-6
xT
2
) + (-1.15x10
-2
xT) + 1.8639
or
where:
T is temperature, and V
O
is the measured output voltage of the LM20.
Output Voltage vs Temperature
DS100908-24
Full-Range Celsius (Centigrade) Temperature Sensor (-55C to +130C)
Operating from a Single Li-Ion Battery Cell
October 1999
LM20
2.4V
,
10A,
SC70,
micro
SMD
T
emperature
Sensor
1999 National Semiconductor Corporation
DS100908
www.national.com
Typical Application
(Continued)
Temperature (T)
Typical V
O
+130C
+303 mV
+100C
+675 mV
+80C
+919 mV
+30C
+1515 mV
Temperature (T)
Typical V
O
+25C
+1574 mV
0C
+1863.9 mV
-30C
+2205 mV
-40C
+2318 mV
-55C
+2485 mV
Connection Diagrams
Ordering Information
Order
Temperature
Temperature
NS Package
Device
Number
Accuracy
Range
Number
Marking
Transport Media
LM20BIM7
2.5C
-55C to +130C
MAA05A
T2B
1000 Units on Tape and Reel
LM20BIM7X
2.5C
-55C to +130C
MAA05A
T2B
3000 Units on Tape and Reel
LM20CIM7
5C
-55C to +130C
MAA05A
T2C
1000 Units on Tape and Reel
LM20CIM7X
5C
-55C to +130C
MAA05A
T2C
3000 Units on Tape and Reel
LM20SIBP
3.5C
-40C to +125C
BPA04DDC
Date
Code
250 Units on Tape and Reel
LM20SIBPX
3.5C
-40C to +125C
BPA04DDC
Date
Code
3000 Units on Tape and Reel
SC70-5
DS100908-1
Note:
-
GND (pin 2) may be grounded or left floating. For optimum thermal
conductivity to the pc board ground plane pin 2 should be grounded.
-
NC (pin 1) should be left floating or grounded. Other signal traces
should not be connected to this pin.
Top View
See NS Package Number MAA05A
micro SMD
DS100908-32
Note:
-
Pin numbers are referenced to the package marking text orientation.
-
Reference JEDEC Registration MO-211, variation BA
-
The actual physical placement of package marking will vary slightly
from part to part. The package marking will designate the date code and
will vary considerably. Package marking does not correlate to device type
in any way.
Top View
See NS Package Number BPA04DDC
LM20
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2
Absolute Maximum Ratings
(Note 1)
Supply Voltage
+6.5V to -0.2V
Output Voltage
(V
+
+ 0.6 V) to
-0.6 V
Output Current
10 mA
Input Current at any pin (Note 2)
5 mA
Storage Temperature
-65C to +150C
Maximum Junction Temperature (T
JMAX
)
+150C
ESD Susceptibility (Note 3) :
Human Body Model
2500 V
Machine Model
250 V
Lead Temperature
SC-70 Package (Note 4) :
Vapor Phase (60 seconds)
+215C
Infrared (15 seconds)
+220C
Operating Ratings
(Note 1)
Specified Temperature Range:
T
MIN
T
A
T
MAX
LM20B, LM20C with
2.4 V
V
+
2.7 V
-30C
T
A
+130C
LM20B, LM20C with
2.7 V
V
+
5.5 V
-55C
T
A
+130C
LM20S with
2.4 V
V
+
5.5 V
-30C
T
A
+125C
LM20S with
2.7 V
V
+
5.5 V
-40C
T
A
+125C
Supply Voltage Range (V
+
)
+2.4 V to +5.5 V
Thermal Resistance,
JA
(Note 5)
SC-70
micro SMD
415C/W
TBDC/W
Electrical Characteristics
Unless otherwise noted, these specifications apply for V
+
= +2.7 V
DC
. Boldface limits apply for T
A
= T
J
= T
MIN
to T
MAX
; all
other limits T
A
= T
J
= 25C; Unless otherwise noted.
Parameter
Conditions
Typical
(Note 6)
LM20B
LM20C
LM20S
Units
(Limit)
Limits
Limits
Limits
(Note 7)
(Note 7)
(Note 7)
Temperature to Voltage Error
V
O
= (-3.88x10
-6
xT
2
)
+ (-1.15x10
-2
xT) + 1.8639V
(Note 8)
T
A
= +25C to +30C
1.5
4.0
2.5
C (max)
T
A
= +130C
2.5
5.0
C (max)
T
A
= +125C
2.5
5.0
3.5
C (max)
T
A
= +100C
2.2
4.7
3.2
C (max)
T
A
= +85C
2.1
4.6
3.1
C (max)
T
A
= +80C
2.0
4.5
3.0
C (max)
T
A
= 0C
1.9
4.4
2.9
C (max)
T
A
= -30C
2.2
4.7
3.3
C (min)
T
A
= -40C
2.3
4.8
3.5
C (max)
T
A
= -55C
2.5
5.0
C (max)
Output Voltage at 0C
+1.8639
V
Variance from Curve
1.0
C
Non-Linearity (Note 9)
-20C
T
A
+80C
0.4
%
Sensor Gain (Temperature
Sensitivity or Average Slope)
to equation:
V
O
=-11.77 mV/CxT+1.860V
-30C
T
A
+100C
-11.77
-11.4
-12.2
-11.0
-12.6
-11.0
-12.6
mV/C (min)
mV/C (max)
Output Impedance
0 A
I
L
+16 A(Notes
11, 12)
160
160
160
(max)
Load Regulation(Note 10)
0 A
I
L
+16 A(Notes
11, 12)
-2.5
-2.5
-2.5
mV (max)
Line Regulation
+2. 4 V
V
+
+5.0V
+3.3
+3.7
+3.7
mV/V (max)
+5.0 V
V
+
+5.5 V
+8.8
+8.9
+8.9
mV (max)
Quiescent Current
+2. 4 V
V
+
+5.5V
4.5
7
7
7
A (max)
+2. 4 V
V
+
+5.0V
4.5
10
10
10
A (max)
Change of Quiescent Current
+2. 4 V
V
+
+5.5V
+0.7
A
Temperature Coefficient of
-11
nA/C
Quiescent Current
Shutdown Current
V
+
+0.8 V
0.02
A
LM20
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3
Electrical Characteristics
(Continued)
Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is func-
tional, but do not guarantee specific performance limits. For guaranteed specifications and test conditions, see the Electrical Characteristics. The guaranteed speci-
fications apply only for the test conditions listed. Some performance characteristics may degrade when the device is not operated under the listed test conditions.
Note 2: When the input voltage (V
I
) at any pin exceeds power supplies (V
I
<
GND or V
I
>
V
+
), the current at that pin should be limited to 5 mA.
Note 3: The human body model is a 100 pF capacitor discharged through a 1.5 k
resistor into each pin. The machine model is a 200 pF capacitor discharged di-
rectly into each pin.
Note 4: See AN-450 "Surface Mounting Methods and Their Effect on Product Reliability" or the section titled "Surface Mount" found in any post 1986 National Semi-
conductor Linear Data Book for other methods of soldering surface mount devices.
Note 5: The junction to ambient thermal resistance (
JA
) is specified without a heat sink in still air using the printed circuit board layout shown in
Figure *NO TARGET
FOR fig NS1382*.
Note 6: Typicals are at T
J
= T
A
= 25C and represent most likely parametric norm.
Note 7: Limits are guaranteed to National's AOQL (Average Outgoing Quality Level).
Note 8: Accuracy is defined as the error between the measured and calculated output voltage at the specified conditions of voltage, current, and temperature (ex-
pressed inC).
Note 9: Non-Linearity is defined as the deviation of the calculated output-voltage-versus-temperature curve from the best-fit straight line, over the temperature range
specified.
Note 10: Regulation is measured at constant junction temperature, using pulse testing with a low duty cycle. Changes in output due to heating effects can be com-
puted by multiplying the internal dissipation by the thermal resistance.
Note 11: Negative currents are flowing into the LM20. Positive currents are flowing out of the LM20. Using this convention the LM20 can at most sink -1 A and
source +16 A.
Note 12: Load regulation or output impedance specifications apply over the supply voltage range of +2.4V to +5.5V.
Note 13: Line regulation is calculated by subtracting the output voltage at the highest supply input voltage from the output voltage at the lowest supply input voltage.
Typical Performance Characteristics
PCB Layouts Used for Thermal
Measurements
Temperature Error vs Temperature
DS100908-25
DS100908-29
a) Layout used for no heat sink measurements.
DS100908-30
b) Layout used for measurements with small heat hink.
FIGURE 1. PCB Lyouts used for thermal measurements.
LM20
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4
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 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:
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
-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
OP
(T
max
) is the calculated output voltage at T
max
using
the parabolic transfer function for V
O
V
OP
(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 lin-
ear transfer function increases with wider 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 +0.02C 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 (
JA
) 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:
T
J
= T
A
+
JA
[(V
+
I
Q
) + (V
+
- V
O
) I
L
]
where I
Q
is the quiescent current and I
L
is 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.
Temperature Range
Linear Equation
V
O
=
Maximum Deviation of Linear
Equation from Parabolic Equation
(C)
T
min
(C)
T
max
(C)
-55
+130
-11.79 mV/C x T + 1.8528 V
1.41
-40
+110
-11.77 mV/C x T + 1.8577 V
0.93
-30
+100
-11.77 mV/C x T + 1.8605 V
0.70
-40
+85
-11.67 mV/C x T + 1.8583 V
0.65
-10
+65
-11.71 mV/C x T + 1.8641 V
0.23
+35
+45
-11.81 mV/C x T + 1.8701 V
0.004
+20
+30
-11.69 mV/C x T + 1.8663 V
0.004
FIGURE 2. First order equations optimized for different temperature ranges.
LM20
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5
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