LM50
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 us-
ing a single positive supply. The LM50’s output voltage is lin-
early proportional to Celsius (Centigrade) temperature
(+10 mV/˚C) and has a DC offset of +500 mV. The offset al-
lows 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 as-
sure low cost and high accuracy. The LM50’s linear output,
+500 mV offset, and factory calibration simplify circuitry re-
quired 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.
Applications
nComputers
nDisk Drives
nBattery Management
nAutomotive
nFAX Machines
nPrinters
nPortable Medical Instruments
nHVAC
nPower Supply Modules
Features
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
Connection Diagram
Order SOT-23 Supplied As
Number Device Marking
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
Typical Application
SOT-23
DS012030-1
Top View
See NS Package Number MA03B
DS012030-3
FIGURE 1. Full-Range Centigrade Temperature Sensor (−40˚C to +125˚C)
July 1999
LM50 SOT-23 Single-Supply Centigrade Temperature Sensor
© 1999 National Semiconductor Corporation DS012030 www.national.com
Absolute Maximum Ratings (Note 1)
Supply Voltage +12V to −0.2V
Output Voltage (+V
S
+ 0.6V) to −1.0V
Output Current 10 mA
Storage Temperature −65˚C to +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
Machine Model 2000V
250V
Operating Ratings (Note 1)
Specified Temperature Range: T
MIN
to T
MAX
LM50C −40˚C to +125˚C
LM50B −25˚C to +100˚C
Operating Temperature Range −40˚C to +150˚C
θ
JA
(Note 4) 450˚C/W
Supply Voltage Range (+V
S
) +4.5V to +10V
Electrical Characteristics
Unless otherwise noted, these specifications apply for V
S
=+5 V
DC
and I
LOAD
=+0.5 µA, in the circuit of
Figure 1
.Boldface
limits apply for the specified T
A
=T
J
=T
MIN
to T
MAX
; all other limits T
A
=T
J
=+25˚C, unless otherwise noted.
Parameter Conditions LM50B LM50C Units
(Limit)
Typical Limit Typical Limit
(Note 5) (Note 5)
Accuracy T
A
=+25˚C ±2.0 ±3.0 ˚C (max)
(Note 6) T
A
=T
MAX
±3.0 ±4.0 ˚C (max)
T
A
=T
MIN
+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 Ω(max)
Line Regulation +4.5V ≤V
S
≤+10V ±0.8 ±0.8 mV/V (max)
(Note 8) ±1.2 ±1.2 mV/V (max)
Quiescent Current +4.5V ≤V
S
≤+10V 130 130 µA (max)
(Note 9) 180 180 µA (max)
Change of Quiescent +4.5V ≤V
S
≤+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
J
=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: See AN-450 “Surface Mounting Methods and Their Effect on Product Reliability” or the section titled “Surface Mount” found in a current National Semicon-
ductor Linear Data Book for other methods of soldering surface mount devices.
Note 3: Human body model, 100 pF discharged through a 1.5 kΩresistor. 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 volt-
age, 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 com-
puted 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 ma-
jority 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.
www.national.com 2
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
DS012030-21
Thermal Time Constant
DS012030-22
Thermal Response in Still Air
with Heat Sink (
Figure 2
)
DS012030-23
Thermal Response
in Stirred Oil Bath
with Heat Sink
DS012030-24
Start-Up Voltage
vs Temperature
DS012030-25
Thermal Response in Still
Air without a Heat Sink
DS012030-26
Quiescent Current vs
Temperature (
Figure 1
)
DS012030-27
Accuracy vs Temperature
DS012030-28
Noise Voltage
DS012030-29
www.national.com3
Typical Performance Characteristics To generate these curves the LM50 was mounted to a printed
circuit board as shown in
Figure 2
. (Continued)
1.0 Mounting
The LM50 can be applied easily in the same way as other
integrated-circuit temperature sensors. It can be glued or ce-
mented 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 ac-
tual temperature of the LM50 die would be at an intermediate
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 cir-
cuit 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 en-
sure that moisture cannot corrode the LM50 or its connec-
tions.
Temperature Rise of LM50 Due to Self-Heating
(Thermal Resistance, θ
JA
)
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
1
⁄
2
" square printed circuit board with 2 oz. foil with part at-
tached 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 kΩoutput 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 kΩ. In an extremely noisy environment it may be nec-
essary to add some filtering to minimize noise pickup. It is
recommended that 0.1 µF be added from V
IN
to GND to by-
Supply Voltage
vs Supply Current
DS012030-30
Start-Up Response
DS012030-31
DS012030-19
FIGURE 2. Printed Circuit Board Used
for Heat Sink to Generate All Curves.
1
⁄
2
" Square Printed Circuit Board
with 2 oz. Foil or Similar
DS012030-7
FIGURE 3. LM50 No Decoupling Required
for Capacitive Load
DS012030-8
FIGURE 4. LM50C with Filter for Noisy Environment
www.national.com 4
2.0 Capacitive Loads (Continued)
pass 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
4kΩoutput 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 re-
sponse time of the LM50 will not be significantly affected. For
much larger capacitors this additional time lag will increase
the overall response time of the LM50.
3.0 Typical Applications
DS012030-17
*R2 ≈2k with a typical 1300 ppm/˚C drift.
FIGURE 5. Block Diagram
DS012030-11
FIGURE 6. Centigrade Thermostat/Fan Controller
DS012030-13
FIGURE 7. Temperature To Digital Converter (Serial Output) (+125˚C Full Scale)
www.national.com5
3.0 Typical Applications (Continued)
DS012030-14
FIGURE 8. Temperature To Digital Converter (Parallel TRI-STATE®Outputs for
Standard Data Bus to µP Interface) (125˚C Full Scale)
DS012030-16
FIGURE 9. LM50 With Voltage-To-Frequency Converter And Isolated Output
(−40˚C to +125˚C; 100 Hz to 1750 Hz)
www.national.com 6
Physical Dimensions inches (millimeters) unless otherwise noted
LIFE SUPPORT POLICY
NATIONAL’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT
DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT AND GENERAL
COUNSEL OF NATIONAL SEMICONDUCTOR CORPORATION. As used herein:
1. Life support devices or systems are devices or
systems which, (a) are intended for surgical implant
into the body, or (b) support or sustain life, and
whose failure to perform when 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 system, or to affect its
safety or effectiveness.
National Semiconductor
Corporation
Americas
Tel: 1-800-272-9959
Fax: 1-800-737-7018
Email: support@nsc.com
National Semiconductor
Europe Fax: +49 (0) 1 80-530 85 86
Email: europe.support@nsc.com
Deutsch Tel: +49 (0) 1 80-530 85 85
English Tel: +49 (0) 1 80-532 78 32
Français Tel: +49 (0) 1 80-532 93 58
Italiano Tel: +49 (0) 1 80-534 16 80
National Semiconductor
Asia Pacific Customer
Response Group
Tel: 65-2544466
Fax: 65-2504466
Email: sea.support@nsc.com
National Semiconductor
Japan Ltd.
Tel: 81-3-5639-7560
Fax: 81-3-5639-7507
www.national.com
SOT-23 Molded Small Outline Transistor Package (M3)
Order Number LM50BIM3, or LM50CIM3
NS Package Number MA03B
LM50 SOT-23 Single-Supply Centigrade Temperature Sensor
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.
