Rainbow Electronics LM50 User Manual

July 1999

LM50
SOT-23 Single-Supply Centigrade Temperature Sensor

LM50 SOT-23 Single-Supply Centigrade Temperature Sensor

General Description

The LM50 is a precision integrated-circuit temperature sen­sor thatcan sense a −40˚C to +125˚C temperature range us­ing asingle positive supply. The LM50’s outputvoltage 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 idealoutput voltageof theLM50 ranges
from +100 mV to +1.75V for a −40˚C to +125˚C temperature
range. The LM50 does not requireany externalcalibration or
trimming toprovide accuracies of

±

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 output,
+500 mV offset, and factory calibration simplify circuitry re­quired in a single supply environment where reading nega­tive temperatures is required. Because the LM50’squiescent
current is less than 130 µA, self-heating is limited to a very
low 0.2˚C in still air.

±

3˚C atroom temperature

Connection Diagram

SOT-23

DS012030-1

See NS Package Number MA03B

Top View

Applications

n Computers
n Disk Drives
n Battery Management
n Automotive
n FAX Machines
n Printers
n Portable Medical Instruments
n HVAC
n Power Supply Modules

Features

n Calibrated directly in degree Celsius (Centigrade)
n Linear + 10.0 mV/˚C scale factor

±

n

2˚C accuracy guaranteed at +25˚C

n Specified for full −40˚ to +125˚C range
n Suitable for remote applications
n Low cost due to wafer-level trimming
n Operates from 4.5V to 10V
n Less than 130 µA current drain
n Low self-heating, less than 0.2˚C in still air
n Nonlinearity less than 0.8˚C over temp

Order SOT-23 Supplied As

Number Device Marking

LM50BIM3 T5B 1000 Units on Tape

LM50CIM3 T5C 1000 Units on Tape

LM50BIM3X T5B 3000 Units on Tape

LM50CIM3X T5C 3000 Units on Tape

and Reel

and Reel

and Reel

and Reel

Typical Application

DS012030-3

FIGURE 1. Full-Range Centigrade Temperature Sensor (−40˚C to +125˚C)

© 1999 National Semiconductor Corporation DS012030 www.national.com

Absolute Maximum Ratings (Note 1)

Supply Voltage +12V to −0.2V
Output Voltage (+V
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

, Maximum

T

JMAX

Junction Temperature 150˚C

+ 0.6V) to −1.0V

S

ESD Susceptibility (Note 3):

Human Body Model
Machine Model

2000V

250V

Operating Ratings (Note 1)

Specified Temperature Range: 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

θ

JA

Supply Voltage Range (+V

) +4.5V to +10V

S

MIN

to T

MAX

Electrical Characteristics

Unless otherwise noted, these specifications apply for V

limits apply for the specified T

=

=

T

A

to T

T

J

MIN

=

+5 V

S

; all other limits T

MAX

and I

DC

Parameter Conditions LM50B LM50C Units

Typical Limit Typical Limit

=

Accuracy T
(Note 6) T

+25˚C

A

=

T

A

MAX

=

T

T

A

MIN

Nonlinearity (Note 7)
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

≤ +10V

S

(Note 8)
Quiescent Current +4.5V ≤ V

≤ +10V 130 130 µA (max)

S

(Note 9) 180 180 µA (max)
Change of Quiescent +4.5V ≤ V

≤ +10V 2.0 2.0 µA (max)

S

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

1000 hours

Note 1: Absolute Maximum Ratingsindicate limits beyondwhich damage tothe device may occur. DC andACelectrical specifications do not apply when operating
the device beyond its rated operating conditions.

Note 2: See AN-450 “SurfaceMounting Methods and Their Effect on Product Reliability” orthe 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 kΩ 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 theerror between the output voltageand 10mv/˚C times the device’s case temperatureplus 500 mV, atspecified 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
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.

Figure 1

.

=

+0.5 µA, in the circuit of

LOAD

=

=

T

+25˚C, unless otherwise noted.

A

J

(Note 5) (Note 5)

±

2.0

±

3.0

+3.0, −3.5

±

0.8

±

0.8

±

1.2

±

0.08 ˚C

±
±
±

±

±

±

Figure 1

. Boldface

(Limit)

3.0 ˚C (max)

4.0 ˚C (max)

4.0 ˚C (max)

0.8 ˚C (max)

0.8 mV/V (max)

1.2 mV/V (max)

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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

.

Thermal Resistance
Junction to Air

Thermal Response
in Stirred Oil Bath
with Heat Sink

Quiescent Current vs
Temperature (

Figure 1

)

DS012030-21

DS012030-24

Thermal Time Constant

Start-Up Voltage
vs Temperature

Accuracy vs Temperature

DS012030-22

DS012030-25

Thermal Response in Still Air
with Heat Sink (

Figure 2

)

DS012030-23

Thermal Response in Still
Air without a Heat Sink

DS012030-26

Noise Voltage

DS012030-27

DS012030-28

DS012030-29

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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)

Supply Voltage
vs Supply Current

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

DS012030-30

DS012030-19

Start-Up Response

DS012030-31

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, 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 is1⁄2" square printed circuitboardwith 2 oz. foil withpart at-

tached as shown in

Figure 2

.

2.0 Capacitive Loads

**

1.0 Mounting

The LM50 can be applied easily in the same way as other
integrated-circuit temperaturesensors. Itcan beglued orce­mented to a surface and its temperature will be within about

0.2˚C of the surface temperature.
This presumes that the ambientair temperatureis almostthe

same as the surface temperature; if the air temperature were
much higher or lower than the surface temperature, the ac­tual temperature of the LM50die wouldbe 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 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 de­sired temperature.

Alternatively, the LM50 can bemounted 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 mustbe keptinsulated 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 coatingsand varnishes such

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DS012030-7

FIGURE 3. LM50 No Decoupling Required

for Capacitive Load

DS012030-8

FIGURE 4. LM50C with Filter for Noisy Environment

The LM50 handles capacitive loading very well. Without any
special precautions,the LM50 can drive anycapacitive load.
The LM50 has a nominal 2 kΩ output 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 kΩ. Inan extremelynoisy environmentit maybe nec­essary to add some filtering to minimize noise pickup. It is
recommended that 0.1 µF be added from V

to GND to by-

IN

2.0 Capacitive Loads (Continued)

pass the power supply voltage, as shown in
noisy environment it may be necessary to add a capacitor
from the output to ground. A 1 µF output capacitor with the
4kΩoutputimpedance will forma 40Hz lowpassfilter.Since

Figure 4

.Ina

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 LM50will notbe significantlyaffected. For
much larger capacitors this additional time lag will increase
the overall response time of the LM50.

*R2 ≈ 2k with a typical 1300 ppm/˚C drift.

3.0 Typical Applications

FIGURE 6. Centigrade Thermostat/Fan Controller

DS012030-17

FIGURE 5. Block Diagram

DS012030-11

DS012030-13

FIGURE 7. Temperature To Digital Converter (Serial Output) (+125˚C Full Scale)

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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)

DS012030-14

FIGURE 9. LM50 With Voltage-To-Frequency Converter And Isolated Output

(−40˚C to +125˚C; 100 Hz to 1750 Hz)

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DS012030-16

Physical Dimensions inches (millimeters) unless otherwise noted

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

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

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.

labeling, can be reasonably expected to result in a
significant injury to the user.

National Semiconductor
Corporation

Americas
Tel: [phone]
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www.national.com

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.

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