July 31, 2008
LM26
SOT-23, ±3°C Accurate, Factory Preset Thermostat
General Description
The LM26 is a precision, single digital-output, low-power ther-
mostat comprised of an internal reference, DAC, temperature
sensor and comparator. Utilizing factory programming, it can
be manufactured with different trip points as well as different
digital output functionality. The trip point (TOS) can be preset
at the factory to any temperature in the range of −55°C to
+110°C in 1°C increments. The LM26 has one digital output
(OS/OS/US/US), one digital input (HYST) and one analog
output (VTEMP). The digital output stage can be preset as ei-
ther open-drain or push-pull. In addition, it can be factory
programmed to be active HIGH or LOW. The digital output
can be factory programmed to indicate an over temperature
shutdown event (OS or OS) or an under temperature shut-
down event (US or US). When preset as an overtemperature
shutdown (OS) it will go LOW to indicate that the die temper-
ature is over the internally preset TOS and go HIGH when the
temperature goes below (TOS–THYST). Similarly, when pre-
programmed as an undertemperature shutdown (US) it will
go HIGH to indicate that the temperature is below TUS and go
LOW when the temperature is above (TUS+THYST). The typical
hysteresis, THYST, can be set to 2°C or 10°C and is controlled
by the state of the HYST pin. A VTEMP analog output provides
a voltage that is proportional to temperature and has a
−10.82mV/°C output slope.
Available parts are detailed in the ordering information. For
other part options, contact a National Semiconductor Distrib-
utor or Sales Representative for information on minimum
order qualification. The LM26 is currently available in a 5-lead
SOT-23 package.
Applications
Microprocessor Thermal Management
Appliances
Portable Battery Powered Systems
Fan Control
Industrial Process Control
HVAC Systems
Remote Temperature Sensing
Electronic System Protection
Features
Internal comparator with pin programmable 2°C or 10°C
hysteresis
No external components required
Open Drain or push-pull digital output; supports CMOS
logic levels
Internal temperature sensor with VTEMP output pin
VTEMP output allows after-assembly system testing
Internal voltage reference and DAC for trip-point setting
Currently available in 5-pin SOT-23 plastic package
Excellent power supply noise rejection
UL Recognized Component
Key Specifications
■ Power Supply Voltage 2.7V to 5.5V
■ Power Supply Current 40µA(max)
20µA(typ)
■ Hysteresis Temperature 2°C or 10°C(typ)
Temperature Trip Point Accuracy
Temperature Range LM26CIM
−55°C to +110°C ±3°C (max)
+120°C ±4°C (max)
LM26CIM5-TPA Simplified Block Diagram and Connection Diagram
10132301
The LM26CIM5-TPA has a fixed trip point of 85°C.
For other trip point and output function availability,
please see ordering information or contact National Semiconductor.
© 2008 National Semiconductor Corporation 101323 www.national.com
LM26 SOT-23, ±3°C Accurate, Factory Preset Thermostat
Ordering Information
For more detailed information on the suffix meaning see the part number template at the end of the Electrical Characteristics
Section. Contact National Semiconductor for other set points and output options.
Order Number
Top Mark
NS Package
Number
Trip Point Setting Output Function
Bulk Rail 3000 Units in Tape &
Reel
LM26CIM5-DPB LM26CIM5X-DPB TDPB MA05B −25°C Open Drain US
LM26CIM5-HHD LM26CIM5X-HHD THHD MA05B 0°C Push Pull US
LM26CIM5-NPA LM26CIM5X-NPA TNPA MA05B 45°C Open Drain OS
LM26CIM5-PHA LM26CIM5X-PHA TPHA MA05B 50°C Open Drain OS
LM26CIM5-RPA LM26CIM5X-RPA TRPA MA05B 65°C Open Drain OS
LM26CIM5-SHA LM26CIM5X-SHA TSHA MA05B 70°C Open Drain OS
LM26CIM5-SPA LM26CIM5X-SPA TSPA MA05B 75°C Open Drain OS
LM26CIM5-TPA LM26CIM5X-TPA TTPA MA05B 85°C Open Drain OS
LM26CIM5-VHA LM26CIM5X-VHA TVHA MA05B 90°C Open Drain OS
LM26CIM5-VPA LM26CIM5X-VPA TVPA MA05B 95°C Open Drain OS
LM26CIM5-XHA LM26CIM5X-XHA TXHA MA05B 100°C Open Drain OS
LM26CIM5-XPA LM26CIM5X-XPA TXPA MA05B 105°C Open Drain OS
LM26CIM5-YHA LM26CIM5X-YHA TYHA MA05B 110°C Open Drain OS
LM26CIM5-YPA LM26CIM5X-YPA TYPA MA05B 115°C Open Drain OS
LM26CIM5-ZHA LM26CIM5X-ZHA TZHA MA05B 120°C Open Drain OS
Connection Diagram
10132302
Pin Descriptions
Pin
Number
Pin
Name
Function Connection
1 HYST Hysteresis control, digital input GND for 10°C or V+ for 2°C
2 GND Ground, connected to the back side of the die
through lead frame.
System GND
3 VTEMP Analog output voltage proportional to
temperature
Leave floating or connect to a high impedance node.
4 V+Supply input 2.7V to 5.5V with a 0.1µF bypass capacitor. For PSRR
information see Section Titled NOISE CONSIDERATIONS.
5 OS Overtemperature Shutdown open-drain active
low thermostat digital output
Controller interrupt, system or power supply shutdown; pull-up
resistor 10kΩ
OS Overtemperature Shutdown push-pull active
high thermostat digital output
Controller interrupt, system or power supply shutdown
US Undertemperature Shutdown open-drain active
low thermostat digital output
System or power supply shutdown; pull-up resistor 10kΩ
US Undertemperature Shutdown push-pull active
high thermostat digital output
System or power supply shutdown
Note: pin 5 functionality and trip point setting are programmed during LM26 manufacture.
www.national.com 2
LM26
Absolute Maximum Ratings (Note 1)
Input Voltage 6.0V
Input Current at any pin (Note 2) 5mA
Package Input Current(Note 2) 20mA
Package Dissipation at TA = 25°C
(Note 3) 500mW
Soldering Information
SOT23 Package
Vapor Phase (60 seconds)
Infrared (15 seconds)
215°C
220°C
Storage Temperature −65°C to + 150°C
ESD Susceptibility (Note 4)
Human Body Model
Machine Model
2500V
250V
Operating Ratings (Note 1)
Specified Temperature Range TMIN TA TMAX
LM26CIM −55°C TA +125°C
Positive Supply Voltage (V+)+2.7V to +5.5V
Maximum VOUT +5.5V
LM26 Electrical Characteristics
The following specifications apply for V+ = 2.7VDC to 5.5VDC, and VTEMP load current = 0µA unless otherwise specified. Boldface
limits apply for TA = TJ = TMIN to TMAX; all other limits TA = TJ = 25°C unless otherwise specified.
Typical LM26CIM Units
Symbol Parameter Conditions (Note 6) Limits (Limits)
(Note 7)
Temperature Sensor
Trip Point Accuracy (Includes VREF, DAC,
Comparator Offset, and Temperature
Sensitivity errors)
-55°C TA +110°C ±3 °C (max)
+120°C ±4 °C (max)
Trip Point Hysteresis HYST = GND 11 °C
HYST = V+2 °C
VTEMP Output Temperature Sensitivity −10.82 mV/°C
VTEMP Temperature Sensitivity Error to
Equation:
VO = (−3.479×10−6×(T−30)2)
+ (−1.082×10−2×(T−30)) + 1.8015V
−30°C TA 120°C,
2.7V V+ 5.5V
±3 °C (max)
−55°C TA 120°C,
4.5V V+ 5.5V
±3 °C (max)
TA = 30°C ±2.5 °C (max)
VTEMP Load Regulation Source 1 μA0.070 mV
Sink 40 μA 0.7 mV (max)
VTEMP Line Regulation +2.7V V+ +5.5V,
−30°C TA +120°C
−0.2 mV/V
ISSupply Current 16 20
40
µA (max)
µA (max)
Digital Output and Input
IOUT(“1”) Logical “1” Output Leakage Current
(Note 9)
V+ = +5.0V 0.001 1 µA (max)
VOUT(“0”) Logical “0” Output Voltage IOUT = +1.2mA and
V+2.7V; IOUT = +3.2mA
and V+4.5V; (Note 8)
0.4 V (max)
VOUT(“1”) Logical “1” Push-Pull Output Voltage ISOURCE = 500µA, V+
2.7V
0.8 × V+V (min)
ISOURCE = 800µA, V
+4.5V
V+ − 1.5 V (min)
VIH HYST Input Logical ”1“ Threshold
Voltage
0.8 × V+V (min)
VIL HYST Input Logical ”0“ Threshold
Voltage
0.2 × V+V (max)
3 www.national.com
LM26
Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is
functional, but do not guarantee specific performance limits. For guaranteed specifications and test conditions, see the Electrical Characteristics. The guaranteed
specifications apply only for the test conditions listed. Some performance characteristics may degrade when the device is not operated under the listed test
conditions.
Note 2: When the input voltage (VI) at any pin exceeds the power supply (VI < GND or VI > V+), the current at that pin should be limited to 5mA. The 20mA
maximum package input current rating limits the number of pins that can safely exceed the power supplies with an input current of 5mA to four. Under normal
operating conditions the maximum current that pins 2, 4 or 5 can handle is limited to 5mA each.
Note 3: The maximum power dissipation must be derated at elevated temperatures and is dictated by TJmax (maximum junction temperature), θJA (junction to
ambient thermal resistance) and TA (ambient temperature). The maximum allowable power dissipation at any temperature is PD = (TJmax–TA)/θJA or the number
given in the Absolute Maximum Ratings, whichever is lower. For this device, TJmax = 150°C. For this device the typical thermal resistance (θJA) of the different
package types when board mounted follow:
Package Type θJA
SOT23-5, MA05B 250°C/W
Note 4: The human body model is a 100pF capacitor discharge through a 1.5kΩ resistor into each pin. The machine model is a 200pF capacitor discharged
directly into each pin.
Note 5: See the URL ”http://www.national.com/packaging/“ for other recommendations and methods of soldering surface mount devices.
Note 6: Typicals are at TJ = TA = 25°C and represent most likely parametric norm.
Note 7: Limits are guaranteed to National's AOQL (Average Outgoing Quality Level).
Note 8: Care should be taken to include the effects of self heating when setting the maximum output load current. The power dissipation of the LM26 would
increase by 1.28mW when IOUT=3.2mA and VOUT=0.4V. With a thermal resistance of 250°C/W, this power dissipation would cause an increase in the die
temperature of about 0.32°C due to self heating. Self heating is not included in the trip point accuracy specification.
Note 9: The 1µA limit is based on a testing limitation and does not reflect the actual performance of the part. Expect to see a doubling of the current for every
15°C increase in temperature. For example, the 1nA typical current at 25°C would increase to 16nA at 85°C.
Part Number Template
The series of digits labeled xyz in the part number LM26CIM-xyz, describe the set point value and the function of the output as
follows:
The place holders xy describe the set point temperature as shown in the following table.
x (10x) y (1x) Temperature (°C)
A - −5
B - −4
C - −3
D - −2
E - −1
F - −0
H H 0
J J 1
K K 2
L L 3
x (10x) y (1x) Temperature (°C)
N N 4
P P 5
R R 6
S S 7
T T 8
V V 9
X - 10
Y - 11
Z - 12
The value of z describes the assignment/function of the output as shown in the following table:
Active-Low/High Open-Drain/ Push-
Pull OS/US Value of z Digital Output Function
0 0 0 A Active-Low, Open-Drain, OS output
0 0 1 B Active-Low, Open-Drain, US output
1 1 0 C Active-High, Push-Pull, OS output
1 1 1 D Active-High, Push-Pull, US output
For example:
the part number LM26CIM5-TPA has TOS = 85°C, and programmed as an active-low open-drain overtemperature shutdown
output.
the part number LM26CIM5-FPD has TUS = −5°C, and programmed as an active-high, push-pull undertemperature shutdown
output.
Active-high open-drain and active-low push-pull options are available, please contact National Semiconductor for more information.
www.national.com 4
LM26
Functional Description
LM26 OPTIONS
10132312
LM26-_ _A
10132313
LM26-_ _B
10132314
LM26-_ _C
10132315
LM26-_ _D
FIGURE 1. Output Pin Options Block Diagrams
The LM26 can be factory programmed to have a trip point
anywhere in the range of −55°C to +110°C.
Applications Hints
AFTER-ASSEMBLY PCB TESTING
The LM26's VTEMP output allows after-assembly PCB testing
by following a simple test procedure. Simply measuring the
VTEMP output voltage will verify that the LM26 has been as-
sembled properly and that its temperature sensing circuitry is
functional. The VTEMP output has very weak drive capability
that can be overdriven by 1.5mA. Therefore, one can simply
force the VTEMP voltage to cause the digital output to change
state, thereby verifying that the comparator and output cir-
cuitry function after assembly. Here is a sample test proce-
dure that can be used to test the LM26CIM5-TPA which has
an 85°C trip point.
1. Turn on V+ and measure VTEMP. Then calculate the
temperature reading of the LM26 using the equation:
VO = (−3.479×10−6×(T−30)2) + (−1.082×10−2×(T
−30)) + 1.8015V (1)
or
(2)
2. Verify that the temperature measured in step one is
within (±3°C + error of reference temperature sensor) of
the ambient/board temperature. The ambient/board
temperature (reference temperature) should be
measured using an extremely accurate calibrated
temperature sensor.
3.
A. Observe that OS is high.
B. Drive VTEMP to ground.
C. Observe that OS is now low.
D. Release the VTEMP pin.
E. Observe that OS is now high.
4.
A. Observe that OS is high.
B. Drive VTEMP voltage down gradually.
C. When OS goes low, note the VTEMP voltage.
D. VTEMPTrig = VTEMP at OS trigger (HIGH->LOW)
E. Calculate Ttrig using Equation 2.
5.
A. Gradually raise VTEMP until OS goes HIGH. Note
VTEMP.
B. Calculate THYST using Equation 2.
VTEMP LOADING
The VTEMP output has very weak drive capability (1 µA source,
40 µA sink). So care should be taken when attaching circuitry
to this pin. Capacitive loading may cause the VTEMP output to
oscillate. Simply adding a resistor in series as shown in Figure
2 will prevent oscillations from occurring. To determine the
value of the resistor follow the guidelines given in Table 1. The
same value resistor will work for either placement of the re-
sistor. If an additional capacitive load is placed directly on the
LM26 output, rather than across CLOAD, it should be at least
a factor of 10 smaller than CLOAD.
5 www.national.com
LM26
TABLE 1. Resistive compensation for capacitive loading
of VTEMP
CLOAD R (Ω)
100pF 0
1nF 8200
10nF 3000
100nF 1000
1µF 430
10132317
a) R in series with capacitor
10132318
b) R in series with signal path
FIGURE 2. Resistor placement for capacitive loading
compensation of VTEMP
NOISE CONSIDERATIONS
The LM26 has excellent power supply noise rejection. Listed
below is a variety of signals used to test the LM26 power sup-
ply rejection. False triggering of the output was not observed
when these signals where coupled into the V+ pin of the
LM26.
square wave 400kHz, 1Vp-p
square wave 2kHz, 200mVp-p
sine wave 100Hz to 1MHz, 200mVp-p
Testing was done while maintaining the temperature of the
LM26 one degree centigrade way from the trip point with the
output not activated.
MOUNTING CONSIDERATIONS
The LM26 can be applied easily in the same way as other
integrated-circuit temperature sensors. It can be glued or ce-
mented to a surface. The temperature that the LM26 is sens-
ing will be within about +0.06°C of the surface temperature to
which the LM26's leads are attached to.
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 measured would be at an intermediate temper-
ature between the surface temperature and the air tempera-
ture.
To ensure good thermal conductivity, the backside of the
LM26 die is directly attached to the GND pin (pin 2). The tem-
peratures of the lands and traces to the other leads of the
LM26 will also affect the temperature that is being sensed.
Alternatively, the LM26 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 LM26 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 LM26 or its connections.
The junction to ambient thermal resistance (θJA) is the pa-
rameter used to calculate the rise of a part's junction temper-
ature due to its power dissipation. For the LM26 the equation
used to calculate the rise in the die junction temperature is as
follows:
(3)
where TA is the ambient temperature, V+ is the power supply
voltage, IQ is the quiescent current, IL_TEMP is the load current
on the VTEMP output, VDO is the voltage on the digital output,
and IDO is the load current on the digital output. Since the
LM26's junction temperature is the actual temperature being
measured, care should be taken to minimize the load current
that the LM26 is required to drive.
The tables shown in Figure 3 summarize the thermal resis-
tance for different conditions and the rise in die temperature
of the LM26 without any loading on VTEMP and a 10k pull-up
resistor on an open-drain digital output with a 5.5V power
supply.
SOT23-5
no heat sink
SOT23-5
small heat sink
θJA
(°C/W)
TJ−TA
(°C)
θJA
(°C/W)
TJ−TA
(°C)
Still Air 250 0.11 TBD TBD
Moving Air TBD TBD TBD TBD
FIGURE 3. Thermal resistance (θJA) and temperature rise
due to self heating (TJ−TA)
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LM26
Typical Applications
10132303
Note: The fan's control pin has internal pull-up. The 10k pull-down sets a slow fan speed. When the output of the LM26 goes low, the fan will speed up.
FIGURE 4. Two Speed Fan Speed Control
10132320
FIGURE 5. Fan High Side Drive
10132321
FIGURE 6. Fan Low Side Drive
7 www.national.com
LM26
10132322
FIGURE 7. Audio Power Amplifier Thermal Protection
10132323
FIGURE 8. Simple Thermostat
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LM26
Physical Dimensions inches (millimeters) unless otherwise noted
5-Lead Molded SOT-23 Plastic Package, JEDEC
Order Number LM26CIM5 or LM26CIM5X
NS Package Number MA05B
9 www.national.com
LM26
Notes
LM26 SOT-23, ±3°C Accurate, Factory Preset Thermostat
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