LM45
SOT-23 Precision Centigrade Temperature Sensors
General Description
The LM45 series are precision integrated-circuit temperature
sensors, whose output voltage is linearly proportional to the
Celsius (Centigrade) temperature. The LM45 does not re-
quire any external calibration or trimming to provide accura-
cies of
2C at room temperature and
3C over a full -20 to
+100C temperature range. Low cost is assured by trimming
and calibration at the wafer level. The LM45's low output im-
pedance, linear output, and precise inherent calibration
make interfacing to readout or control circuitry especially
easy. It can be used with a single power supply, or with plus
and minus supplies. As it draws only 120 A from its supply,
it has very low self-heating, less than 0.2C in still air. The
LM45 is rated to operate over a -20 to +100C temperature
range.
Applications
n
Battery Management
n
FAX Machines
n
Printers
n
Portable Medical Instruments
n
HVAC
n
Power Supply Modules
n
Disk Drives
n
Computers
n
Automotive
Features
n
Calibrated directly in Celsius (Centigrade)
n
Linear + 10.0 mV/C scale factor
n
3C accuracy guaranteed
n
Rated for full -20 to +100C range
n
Suitable for remote applications
n
Low cost due to wafer-level trimming
n
Operates from 4.0V to 10V
n
Less than 120 A current drain
n
Low self-heating, 0.20C in still air
n
Nonlinearity only
0.8C max over temp
n
Low impedance output, 20
for 1 mA load
Connection Diagram
SOT-23
Order
Device
Number
Marking
Supplied As
LM45BIM3
T4B
1000 Units on Tape and Reel
LM45BIM3X
T4B
3000 Units on Tape and Reel
LM45CIM3
T4C
1000 Units on Tape and Reel
LM45CIM3X
T4C
3000 Units on Tape and Reel
Typical Applications
SOT-23
DS011754-1
Top View
See NS Package Number MA03B
DS011754-3
FIGURE 1. Basic Centigrade Temperature
Sensor (+2.5C to +100C)
DS011754-4
Choose R
1
= -V
S
/50 A
V
OUT
= (10 mV/C x Temp C)
V
OUT
= +1,000 mV at +100C
= +250 mV at +25C
= -200 mV at -20C
FIGURE 2. Full-Range Centigrade
Temperature Sensor (-20C to +100C)
July 1999
LM45
SOT-23
Precision
Centigrade
T
emperature
Sensors
1999 National Semiconductor Corporation
DS011754
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
-65C to +150C
Lead Temperature:
SOT Package (Note 2):
Vapor Phase (60 seconds)
215C
Infrared (15 seconds)
220C
ESD Susceptibility (Note 3):
Human Body Model
Machine Model
2000V
250V
Operating Ratings
(Note 1)
Specified Temperature Range
(Note 4)
T
MIN
to T
MAX
LM45B, LM45C
-20C to +100C
Operating Temperature Range
LM45B, LM45C
-40C to +125C
Supply Voltage Range (+V
S
)
+4.0V to +10V
Electrical Characteristics
Unless otherwise noted, these specifications apply for +V
S
= +5Vdc and I
LOAD
= +50 A, in the circuit of Figure 2. These
specifications also apply from +2.5C to T
MAX
in the circuit of
Figure 1 for +V
S
= +5Vdc. 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
LM45B
LM45C
Units
(Limit)
Typical
Limit
Typical
Limit
(Note 5)
(Note 5)
Accuracy
T
A
=+25C
2.0
3.0
C (max)
(Note 6)
T
A
=T
MAX
3.0
4.0
C (max)
T
A
=T
MIN
3.0
4.0
C (max)
Nonlinearity
T
MIN
T
A
T
MAX
0.8
0.8
C (max)
(Note 7)
Sensor Gain
T
MIN
T
A
T
MAX
+9.7
+9.7
mV/C (min)
(Average Slope)
+10.3
+10.3
mV/C (max)
Load Regulation (Note 8)
0
I
L
+1 mA
35
35
mV/mA
(max)
Line Regulation
+4.0V
+V
S
+10V
0.80
0.80
mV/V (max)
(Note 8)
1.2
1.2
mV/V (max)
Quiescent Current
+4.0V
+V
S
+10V, +25C
120
120
A (max)
(Note 9)
+4.0V
+V
S
+10V
160
160
A (max)
Change of Quiescent
4.0V
+V
S
10V
2.0
2.0
A (max)
Current (Note 9)
Temperature Coefficient
+2.0
+2.0
A/C
of Quiescent Current
Minimum Temperature
In circuit of
+2.5
+2.5
C (min)
for Rated Accuracy
Figure 1, I
L
=0
Long Term Stability (Note 10)
T
J
=T
MAX
, for 1000 hours
0.12
0.12
C
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 k
resistor. Machine model, 200 pF discharged directly into each pin.
Note 4: Thermal resistance of the SOT-23 package is 260C/W, junction to ambient when attached to a printed circuit board with 2 oz. foil as shown in
Figure 3.
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 10 mv/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 com-
puted by multiplying the internal dissipation by the thermal resistance.
Note 9: Quiescent current is measured using 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.
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Typical Performance Characteristics
To generate these curves the LM45 was mounted to a printed
circuit board as shown in
Figure 3.
Thermal Resistance
Junction to Air
DS011754-24
Thermal Time Constant
DS011754-25
Thermal Response in Still Air
with Heat Sink (
Figure 3)
DS011754-26
Thermal Response
in Stirred Oil Bath
with Heat Sink
DS011754-27
Start-Up Voltage
vs Temperature
DS011754-28
Quiescent Current
vs Temperature
(In Circuit of
Figure 1)
DS011754-29
Quiescent Current
vs Temperature
(In Circuit of
Figure 2)
DS011754-30
Accuracy vs Temperature
(Guaranteed)
DS011754-31
Noise Voltage
DS011754-32
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3
Typical Performance Characteristics
To generate these curves the LM45 was mounted to a printed
circuit board as shown in
Figure 3. (Continued)
Applications
The LM45 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
0.2C 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 LM45 die would be at an intermediate
temperature between the surface temperature and the air
temperature.
To ensure good thermal conductivity the backside of the
LM45 die is directly attached to the GND pin. The lands and
traces to the LM45 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 LM45s temperature to deviate from the de-
sired temperature.
Alternatively, the LM45 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 LM45 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 in-
sure that moisture cannot corrode the LM45 or its connec-
tions.
Temperature Rise of LM45 Due to Self-Heating
(Thermal Resistance)
SOT-23
SOT-23
no heat sink
*
small heat fin
**
Still air
450C/W
260C/W
Moving air
180C/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 3.
Supply Voltage
vs Supply Current
DS011754-33
Start-Up Response
DS011754-34
DS011754-23
FIGURE 3. Printed Circuit Board Used for Heat Sink to Generate All Curves.
1
/
2
" Square Printed Circuit Board with 2 oz. Foil or Similar
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4
Typical Applications
CAPACITIVE LOADS
Like most micropower circuits, the LM45 has a limited ability
to drive heavy capacitive loads. The LM45 by itself is able to
drive 500 pF without special precautions. If heavier loads are
anticipated, it is easy to isolate or decouple the load with a
resistor; see
Figure 4. Or you can improve the tolerance of
capacitance with a series R-C damper from output to
ground; see
Figure 5.
Any linear circuit connected to wires in a hostile environment
can have its performance affected adversely by intense elec-
tromagnetic sources such as relays, radio transmitters, mo-
tors with arcing brushes, SCR transients, etc, as its wiring
can act as a receiving antenna and its internal junctions can
act as rectifiers. For best results in such cases, a bypass ca-
pacitor from V
IN
to ground and a series R-C damper such as
75
in series with 0.2 or 1 F from output to ground, as
shown in
Figure 5, are often useful.
DS011754-8
FIGURE 4. LM45 with Decoupling from Capacitive Load
DS011754-9
FIGURE 5. LM45 with R-C Damper
DS011754-12
FIGURE 6. Temperature Sensor,
Single Supply, -20C to +100C
DS011754-14
FIGURE 7. 4-to-20 mA Current Source (0C to +100C)
DS011754-15
FIGURE 8. Fahrenheit Thermometer
DS011754-16
FIGURE 9. Centigrade Thermometer (Analog Meter)
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