LM50 SOT-23 Single-Supply Centigrade Temperature Sensor
Literature Number: SNIS118C
SOT-23 Single-Supply Centigrade Temperature Sensor
General Description
The LM50 is a precision integrated-circuit temperature sen-
sor that can sense a −40˚C to +125˚C temperature range
using a single positive supply. The LM50’s output voltage is
linearly proportional to Celsius (Centigrade) temperature
(+10 mV/˚C) and has a DC offset of +500 mV. The offset
allows reading negative temperatures without the need for a
negative supply. The ideal output voltage of the LM50 ranges
from +100 mV to +1.75V for a −40˚C to +125˚C temperature
range. The LM50 does not require any external calibration or
trimming to provide accuracies of ±3˚C at room temperature
and ±4˚C over the full −40˚C to +125˚C temperature range.
Trimming and calibration of the LM50 at the wafer level
assure low cost and high accuracy. The LM50’s linear out-
put, +500 mV offset, and factory calibration simplify circuitry
required in a single supply environment where reading nega-
tive temperatures is required. Because the LM50’s quiescent
current is less than 130 µA, self-heating is limited to a very
low 0.2˚C in still air.
nDisk Drives
nBattery Management
nFAX Machines
nPortable Medical Instruments
nPower Supply Modules
nCalibrated directly in degree Celsius (Centigrade)
nLinear + 10.0 mV/˚C scale factor
n±2˚C accuracy guaranteed at +25˚C
nSpecified for full −40˚ to +125˚C range
nSuitable for remote applications
nLow cost due to wafer-level trimming
nOperates from 4.5V to 10V
nLess than 130 µA current drain
nLow self-heating, less than 0.2˚C in still air
nNonlinearity less than 0.8˚C over temp
nUL Recognized Component
Connection Diagram
Top View
See NS Package Number mf03A
Order Device Supplied As
Number Top Mark
LM50BIM3 T5B 1000 Units on Tape
and Reel
LM50CIM3 T5C 1000 Units on Tape
and Reel
LM50BIM3X T5B 3000 Units on Tape
and Reel
LM50CIM3X T5C 3000 Units on Tape
and Reel
February 2006
LM50 SOT-23 Single-Supply Centigrade Temperature Sensor
© 2006 National Semiconductor Corporation DS012030 www.national.com
Typical Application
FIGURE 1. Full-Range Centigrade Temperature Sensor (−40˚C to +125˚C)
www.national.com 2
Absolute Maximum Ratings (Note 1)
Supply Voltage +12V to −0.2V
Output Voltage (+V
+ 0.6V) to −1.0V
Output Current 10 mA
Storage Temperature −65˚C to +150˚C
, Maximum
Junction Temperature 150˚C
ESD Susceptibility (Note 3):
Human Body Model
Machine Model
Operating Ratings (Note 1)
Specified Temperature Range: T
to T
LM50C −40˚C to +125˚C
LM50B −25˚C to +100˚C
Operating Temperature Range −40˚C to +150˚C
(Note 4) 450˚C/W
Supply Voltage Range (+V
) +4.5V to +10V
Soldering process must comply with National Semiconduc-
tor’s Reflow Temperature Profile specifications. Refer to
www.national.com/packaging. (Note 2)
Electrical Characteristics
Unless otherwise noted, these specifications apply for V
and I
= +0.5 µA, in the circuit of Figure 1.Boldface
limits apply for the specified T
to T
; all other limits T
= +25˚C, unless otherwise noted.
Parameter Conditions LM50B LM50C Units
Typical Limit Typical Limit
(Note 5) (Note 5)
Accuracy T
= +25˚C ±2.0 ±3.0 ˚C (max)
(Note 6) T
±3.0 ±4.0 ˚C (max)
+3.0, −3.5 ±4.0 ˚C (max)
Nonlinearity (Note 7) ±0.8 ±0.8 ˚C (max)
Sensor Gain +9.7 +9.7 mV/˚C (min)
(Average Slope) +10.3 +10.3 mV/˚C (max)
Output Resistance 2000 4000 2000 4000 (max)
Line Regulation +4.5V V
+10V ±0.8 ±0.8 mV/V (max)
(Note 8) ±1.2 ±1.2 mV/V (max)
Quiescent Current +4.5V V
+10V 130 130 µA (max)
(Note 9) 180 180 µA (max)
Change of Quiescent +4.5V V
+10V 2.0 2.0 µA (max)
Current (Note 9)
Temperature Coefficient of +1.0 +2.0 µA/˚C
Quiescent Current
Long Term Stability (Note 10) T
= 125˚C, for ±0.08 ±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: Reflow temperature profiles are different for lead-free and non-lead-free packages.
Note 3: Human body model, 100 pF discharged through a 1.5 kresistor. 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 plus 500 mV, 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
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.
Typical Performance Characteristics To generate these curves the LM50 was mounted to a printed
circuit board as shown in Figure 2.
Thermal Resistance
Junction to Air Thermal Time Constant
01203021 01203022
Thermal Response in Still Air
with Heat Sink (Figure 2)
Thermal Response
in Stirred Oil Bath
with Heat Sink
01203023 01203024
Start-Up Voltage
vs Temperature
Thermal Response in Still
Air without a Heat Sink
01203025 01203026
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Typical Performance Characteristics To generate these curves the LM50 was mounted to a printed
circuit board as shown in Figure 2. (Continued)
Quiescent Current vs
Temperature (Figure 1) Accuracy vs Temperature
01203027 01203028
Noise Voltage
Supply Voltage
vs Supply Current
01203029 01203030
Start-Up Response
Printed Circuit Board
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 interme-
diate 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 being
measured. These printed circuit board lands and traces will
not cause the LM50s temperature to deviate from the de-
sired 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 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 LM50 or its connec-
Temperature Rise of LM50 Due to Self-Heating
(Thermal Resistance, θ
SOT-23 SOT-23
no heat sink* small heat fin**
Still air 450˚C/W 260˚C/W
Moving air 180˚C/W
* Part soldered to 30 gauge wire.
** Heat sink used is
" square printed circuit board with 2 oz. foil with part
attached as shown in Figure 2.
2.0 Capacitive Loads
The LM50 handles capacitive loading very well. Without any
special precautions, the LM50 can drive any capacitive load.
The LM50 has a nominal 2 koutput impedance (as can be
seen in the block diagram). The temperature coefficient of
the output resistors is around 1300 ppm/˚C. Taking into
account this temperature coefficient and the initial tolerance
of the resistors the output impedance of the LM50 will not
exceed 4 k. In an extremely noisy environment it may be
necessary to add some filtering to minimize noise pickup. It
is recommended that 0.1 µF be added from V
to GND to
bypass the power supply voltage, as shown in Figure 4.Ina
noisy environment it may be necessary to add a capacitor
from the output to ground. A 1 µF output capacitor with the
4koutput 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.
FIGURE 2. Printed Circuit Board Used
for Heat Sink to Generate All Curves.
" Square Printed Circuit Board
with 2 oz. Foil or Similar
FIGURE 3. LM50 No Decoupling Required
for Capacitive Load
FIGURE 4. LM50C with Filter for Noisy Environment
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2.0 Capacitive Loads (Continued)
3.0 Typical Applications
*R2 2k with a typical 1300 ppm/˚C drift.
FIGURE 5. Block Diagram
FIGURE 6. Centigrade Thermostat/Fan Controller
FIGURE 7. Temperature To Digital Converter (Serial Output) (+125˚C Full Scale)
3.0 Typical Applications (Continued)
FIGURE 8. Temperature To Digital Converter (Parallel TRI-STATE®Outputs for
Standard Data Bus to µP Interface) (125˚C Full Scale)
FIGURE 9. LM50 With Voltage-To-Frequency Converter And Isolated Output
(−40˚C to +125˚C; 100 Hz to 1750 Hz)
www.national.com 8
Physical Dimensions inches (millimeters) unless otherwise noted
SOT-23 Molded Small Outline Transistor Package (M3)
Order Number LM50BIM3, or LM50CIM3
NS Package Number mf03a
National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves
the right at any time without notice to change said circuitry and specifications.
For the most current product information visit us at www.national.com.
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properly used in accordance with instructions for use
provided in the labeling, can be reasonably expected to result
in a significant injury to the user.
2. A critical component is any component of a life support
device or system whose failure to perform can be reasonably
expected to cause the failure of the life support device or
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LM50 SOT-23 Single-Supply Centigrade Temperature Sensor
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