TL H 12030
LM50BLM50C
SOT-23
Single-Supply
Centigrade
Temperature
Sensor
June 1996
LM50B LM50C
SOT-23 Single-Supply Centigrade Temperature Sensor
General Description
The LM50 is a precision integrated-circuit temperature sen-
sor that can sense a
b
40 C to
a
125 C temperature range
using a single positive supply The LM50's output voltage is
linearly proportional to Celsius (Centigrade) temperature
(
a
10 mV C) and has a DC offset of
a
500 mV The offset
allows reading negative temperatures without the need for a
negative supply The ideal output voltage of the LM50
ranges from
a
100 mV to
a
1 75V for a
b
40 C to
a
125 C
temperature range The LM50 does not require any external
calibration or trimming to provide accuracies of
g
3 C at
room temperature and
g
4 C over the full
b
40 C to
a
125 C temperature range Trimming and calibration of the
LM50 at the wafer level assure low cost and high accuracy
The LM50's linear output
a
500 mV offset and factory cali-
bration simplify circuitry required in a single supply environ-
ment where reading negative temperatures is required Be-
cause the LM50's quiescent current is less than 130 mA
self-heating is limited to a very low 0 2 C in still air
Applications
Y
Computers
Y
Disk Drives
Y
Battery Management
Y
Automotive
Y
FAX Machines
Y
Printers
Y
Portable Medical Instruments
Y
HVAC
Y
Power Supply Modules
Features
Y
Calibrated directly in
Celsius (Centigrade)
Y
Linear
a
10 0 mV C scale factor
Y
g
2 C accuracy guaranteed at
a
25 C
Y
Specified for full
b
40 to
a
125 C range
Y
Suitable for remote applications
Y
Low cost due to wafer-level trimming
Y
Operates from 4 5V to 10V
Y
Less than 130 mA current drain
Y
Low self-heating less than 0 2 C in still air
Y
Nonlinearity less than 0 8 C over temp
Connection Diagram
SOT-23
TL H 12030 1
Top View
See NS Package Number M03B
(JEDEC Registration TO-236AB)
Order
SOT-23
Supplied As
Number
Device Marking
LM50BIM3
T5B
250 Units on Tape and Reel
LM50CIM3
T5C
250 Units on Tape and Reel
LM50BIM3X
T5B
3000 Units on Tape and Reel
LM50CIM3X
T5C
3000 Units on Tape and Reel
Typical Application
TL H 12030 3
FIGURE 1 Full-Range Centigrade Temperature Sensor (
b
40 C to
a
125 C)
C1996 National Semiconductor Corporation
RRD-B30M76 Printed in U S A
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Absolute Maximum Ratings
(Note 1)
Supply Voltage
a
12V to
b
0 2V
Output Voltage
(
a
V
S
a
0 6V) to
b
1 0V
Output Current
10 mA
Storage Temperature
b
65 C to
a
150 C
Lead Temperature
SOT Package (Note 2)
Vapor Phase (60 seconds)
215 C
Infrared (15 seconds)
220 C
T
JMAX
Maximum Junction Temperature
150 C
ESD Susceptibility (Note 3)
Human Body Model
2000V
Machine Model
200V
Operating Ratings
(Note 1)
Specified Temperature Range
T
MIN
to T
MAX
LM50C
b
40 C to
a
125 C
LM50B
b
25 C to
a
100 C
Operating Temperature Range
b
40 C to
a
150 C
i
JA
(Note 4)
450 C W
Supply Voltage Range (
a
V
S
)
a
4 5V to
a
10V
Electrical Characteristics
Unless otherwise noted these specifications apply for V
S
e a
5 V
DC
and I
LOAD
e
a
0 5 mA in the circuit of
Figure 1 Boldface limits apply for the specified T
A
e
T
J
e
T
MIN
to T
MAX
all other limits T
A
e
T
J
e a
25 C unless otherwise noted
Parameter
Conditions
LM50B
LM50C
(Limit)
Units
Typical
Limit
Typical
Limit
(Note 5)
(Note 5)
Accuracy
T
A
e a
25 C
g
2 0
g
3 0
C (max)
(Note 6)
T
A
e
T
MAX
g
3 0
g
4 0
C (max)
T
A
e
T
MIN
a
3 0
b
3 5
g
4 0
C (max)
Nonlinearity (Note 7)
g
0 8
g
0 8
C (max)
Sensor Gain
a
9 7
a
9 7
mV C (min)
(Average Slope)
a
10 3
a
10 3
mV C (max)
Output Resistance
2000
4000
2000
4000
X
(max)
Line Regulation
a
4 5V
s
V
S
s
a
10V
g
0 8
g
0 8
mV V (max)
(Note 8)
g
1 2
g
1 2
mV V (max)
Quiescent Current
a
4 5V
s
V
S
s
a
10V
130
130
m
A (max)
(Note 9)
180
180
m
A (max)
Change of Quiescent
a
4 5V
s
V
S
s
a
10V
2 0
2 0
m
A (max)
Current (Note 8)
Temperature Coefficient of
a
1 0
a
2 0
m
A C
Quiescent Current
Long Term Stability (Note 10)
T
J
e
125 C for
g
0 08
g
0 08
C
1000 hours
Note 1
Absolute Maximum Ratings indicate limits beyond which damage to the device may occur DC and AC electrical specifications do not apply when operating
the device beyond its rated operating conditions
Note 2
See AN-450 ``Surface Mounting Methods and Their Effect on Product Reliability'' or the section titled ``Surface Mount'' found in a current National
Semiconductor Linear Data Book for other methods of soldering surface mount devices
Note 3
Human body model 100 pF discharged through a 1 5 kX resistor Machine model 200 pF discharged directly into each pin
Note 4
Thermal resistance of the SOT-23 package is specified without a heat sink junction to ambient
Note 5
Limits are guaranteed to National's AOQL (Average Outgoing Quality Level)
Note 6
Accuracy is defined as the error between the output voltage and 10mv C times the device's case temperature at specified conditions of voltage current
and temperature (expressed in C)
Note 7
Nonlinearity is defined as the deviation of the output-voltage-versus-temperature curve from the best-fit straight line over the device's rated temperature
range
Note 8
Regulation is measured at constant junction temperature using pulse testing with a low duty cycle Changes in output due to heating effects can be
computed by multiplying the internal dissipation by the thermal resistance
Note 9
Quiescent current is defined in the circuit of
Figure 1
Note 10
For best long-term stability any precision circuit will give best results if the unit is aged at a warm temperature and or temperature cycled for at least 46
hours before long-term life test begins This is especially true when a small (Surface-Mount) part is wave-soldered allow time for stress relaxation to occur The
majority of the drift will occur in the first 1000 hours at elevated temperatures The drift after 1000 hours will not continue at the first 1000 hour rate
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2
Typical Performance Characteristics
To generate these curves the LM50 was mounted to a printed circuit board as shown in
Figure 2
Junction to Air
Thermal Resistance
Thermal Time Constant
with Heat Sink (
Figure 2 )
Thermal Response in Still Air
with Heat Sink
in Stirred Oil Bath
Thermal Response
vs Temperature
Start-Up Voltage
Air without a Heat Sink
Thermal Response in Still
Temperature
(Figure 1)
Quiescent Current vs
Accuracy vs Temperature
Noise Voltage
vs Supply Current
Supply Voltage
Start-Up Response
TL H 12030 19
FIGURE 2 Printed Circuit Board Used
for Heat Sink to Generate All Curves
Square Printed Circuit Board
with 2 oz Foil or Similar
TL H 12030 18
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1 0 Mounting
The LM50 can be applied easily in the same way as other
integrated-circuit temperature sensors It can be glued or
cemented to a surface and its temperature will be within
about 0 2 C of the surface temperature
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 of the LM50 die would be at an inter-
mediate temperature between the surface temperature and
the air temperature
To ensure good thermal conductivity the backside of the
LM50 die is directly attached to the GND pin The lands and
traces to the LM50 will of course be part of the printed
circuit board which is the object whose temperature is be-
ing measured These printed circuit board lands and traces
will not cause the LM50s temperature to deviate from the
desired temperature
Alternatively the LM50 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 LM50 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 var-
nishes such as Humiseal and epoxy paints or dips are often
used to ensure that moisture cannot corrode the LM50 or its
connections
Temperature Rise of LM50 Due to Self-Heating
(Thermal Resistance i
JA
)
SOT-23
SOT-23
no heat sink
small heat fin
Still air
450 C W
260 C W
Moving air
180 C W
Heat sink used is
square printed circuit board with 2 oz foil with part
attached as shown in
Figure 2
Part soldered to 30 gauge wire
2 0 Capacitive Loads
TL H 12030 7
FIGURE 3 LM50 No Decoupling Required
for Capacitive Load
TL H 12030 8
FIGURE 4 LM50C with Filter for Noisy Environment
The LM50 handles capacitive loading very well Without any
special precautions the LM50 can drive any capacitive load
The LM50 has a nominal 2 kX output impedance (as can be
seen in the block diagram) The temperature coefficient of
the output resistors is around 1300 ppm C Taking into ac-
count this temperature coefficient and the initial tolerance of
the resistors the output impedance of the LM50 will not ex-
ceed 4 kX In an extremely noisy environment it may be
necessary to add some filtering to minimize noise pickup It
is recommended that 0 1 mF be added from V
IN
to GND to
bypass the power supply voltage as shown in
Figure 4 In a
noisy environment it may be necessary to add a capacitor
from the output to ground A 1 mF output capacitor with the
4 kX output impedance will form a 40 Hz lowpass filter
Since the thermal time constant of the LM50 is much slower
than the 25 ms time constant formed by the RC the overall
response time of the LM50 will not be significantly affected
For much larger capacitors this additional time lag will in-
crease the overall response time of the LM50
TL H 12030 17
R2
2k with a typical 1300 ppm C drift
FIGURE 5 Block Diagram
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3 0 Typical Applications
TL H 12030 11
FIGURE 6 Centigrade Thermostat Fan Controller
TL H 12030 13
FIGURE 7 Temperature To Digital Converter (Serial Output) (
a
125 C Full Scale)
TL H 12030 14
FIGURE 8 Temperature To Digital Converter (Parallel TRI-STATE
Outputs for
Standard Data Bus to mP Interface) (125 C Full Scale)
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