National Semiconductor LM26 Technical data

LM26
SOT-23, ±3°C Accurate, Factory Preset Thermostat

Fan Control

General Description

The LM26 is a precision, single digital-output, low-power ther­mostat 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

/US/US), one digital input (HYST) and one analog

(OS/OS
output (V
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 shut­down event (US or US). When preset as an overtemperature
shutdown (OS) it will go LOW to indicate that the die temper­ature is over the internally preset TOS and go HIGH when the
temperature goes below (TOS–T
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+T
hysteresis, T
by the state of the HYST pin. A V
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 Distrib­utor or Sales Representative for information on minimum
order qualification. The LM26 is currently available in a 5-lead
SOT-23 package.

). The digital output stage can be preset as ei-

TEMP

). Similarly, when pre-

HYST

). The typical

, can be set to 2°C or 10°C and is controlled

HYST

TEMP

HYST

analog output provides

Applications

Microprocessor Thermal Management

■

Appliances

■

Portable Battery Powered Systems

■

■

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 V

■

V

■

■

■

■

■

output allows after-assembly system testing

TEMP

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

TEMP

output pin

Key Specifications

■ Power Supply Voltage 2.7V to 5.5V

■ Power Supply Current

■ 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)

LM26 SOT-23, ±3°C Accurate, Factory Preset Thermostat

July 31, 2008

40µA(max)

20µA(typ)

LM26CIM5-TPA Simplified Block Diagram and Connection Diagram

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

10132301

LM26

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

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

Top Mark

NS Package

Number

Trip Point Setting Output Function

Connection Diagram

10132302

Pin Descriptions

Pin

Number

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

3 V

4 V

5 OS Overtemperature Shutdown open-drain active

Note: pin 5 functionality and trip point setting are programmed during LM26 manufacture.

Pin

Name

through lead frame.

Analog output voltage proportional to

TEMP

temperature

+

Supply input 2.7V to 5.5V with a 0.1µF bypass capacitor. For PSRR

low thermostat digital output

OS Overtemperature Shutdown push-pull active

high thermostat digital output

US Undertemperature Shutdown open-drain active

low thermostat digital output

US Undertemperature Shutdown push-pull active

high thermostat digital output

Function Connection

System GND

Leave floating or connect to a high impedance node.

information see Section Titled NOISE CONSIDERATIONS.

Controller interrupt, system or power supply shutdown; pull-up
resistor ≥ 10kΩ

Controller interrupt, system or power supply shutdown

System or power supply shutdown; pull-up resistor ≥ 10kΩ

System or power supply shutdown

www.national.com 2

LM26

Absolute Maximum Ratings (Note 1)

Input Voltage 6.0V
Input Current at any pin (Note 2) 5mA

Storage Temperature −65°C to + 150°C
ESD Susceptibility (Note 4)

Human Body Model
Machine Model

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

Operating Ratings (Note 1)

Specified Temperature Range

LM26CIM

Positive Supply Voltage (V+)

Maximum V

OUT

T

≤ TA ≤ T

MIN

−55°C ≤ TA ≤ +125°C

+2.7V to +5.5V

LM26 Electrical Characteristics

The following specifications apply for V+ = 2.7VDC to 5.5VDC, and V

limits apply for TA = TJ = T

MIN

to T

; all other limits TA = TJ = 25°C unless otherwise specified.

MAX

Typical LM26CIM Units

Symbol Parameter Conditions

Temperature Sensor

Trip Point Accuracy (Includes V

Comparator Offset, and Temperature

REF

, DAC,

-55°C ≤ TA ≤ +110°C

+120°C ±4 °C (max)

Sensitivity errors)

Trip Point Hysteresis HYST = GND 11 °C

HYST = V

V

V

Output Temperature Sensitivity

TEMP

Temperature Sensitivity Error to

TEMP

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

−55°C ≤ TA ≤ 120°C,

4.5V ≤ V+ ≤ 5.5V

TA = 30°C ±2.5 °C (max)

V

Load Regulation

TEMP

Source ≤ 1 μA
Sink ≤ 40 μA

V

Line Regulation

TEMP

+2.7V ≤ V+ ≤ +5.5V,

−30°C ≤ TA ≤ +120°C

I

S

Supply Current 16 20

Digital Output and Input

I

OUT(“1”)

Logical “1” Output Leakage Current

V+ = +5.0V 0.001 1 µA (max)

(Note 9)

V

OUT(“0”)

V

OUT(“1”)

Logical “0” Output Voltage I

Logical “1” Push-Pull Output Voltage

= +1.2mA and

OUT

+

V

≥2.7V; I

+

and V

≥4.5V; (Note 8)

I

= 500µA, V+ ≥

SOURCE

2.7V

I

= 800µA, V

SOURCE

+

≥4.5V

V

IH

HYST Input Logical ”1“ Threshold

0.8 × V

Voltage

V

IL

HYST Input Logical ”0“ Threshold

0.2 × V

Voltage

load current = 0µA unless otherwise specified. Boldface

TEMP

(Note 6)

Limits

(Note 7)

±3 °C (max)

+

2

−10.82

°C

±3 °C (max)

±3 °C (max)

0.070 mV

0.7 mV (max)

−0.2 mV/V

40

0.4 V (max)

= +3.2mA

OUT

0.8 × V

+

V+ − 1.5 V (min)

+

+

(Limits)

mV/°C

µA (max)
µA (max)

V (min)

V (min)

V (max)

2500V

250V

MAX

+5.5V

3 www.national.com

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

LM26

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 T
ambient thermal resistance) and TA (ambient temperature). The maximum allowable power dissipation at any temperature is PD = (T
given in the Absolute Maximum Ratings, whichever is lower. For this device, T
package types when board mounted follow:

= 150°C. For this device the typical thermal resistance (θJA) of the different

Jmax

(maximum junction temperature), θJA (junction to

Jmax

)/θJA or the number

Jmax–TA

Package Type

θ

JA

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 I
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.

=3.2mA and V

OUT

=0.4V. With a thermal resistance of 250°C/W, this power dissipation would cause an increase in the die

OUT

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

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

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

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

Functional Description

LM26 OPTIONS

LM26

LM26-_ _A

LM26-_ _C

10132312

10132314

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 V
by following a simple test procedure. Simply measuring the
V

output voltage will verify that the LM26 has been as-

TEMP

sembled properly and that its temperature sensing circuitry is
functional. The V
that can be overdriven by 1.5mA. Therefore, one can simply
force the V
state, thereby verifying that the comparator and output cir­cuitry function after assembly. Here is a sample test proce­dure that can be used to test the LM26CIM5-TPA which has
an 85°C trip point.

1.

Turn on V+ and measure V
temperature reading of the LM26 using the equation:

VO = (−3.479×10−6×(T−30)2) + (−1.082×10−2×(T

or

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.

output allows after-assembly PCB testing

TEMP

output has very weak drive capability

TEMP

voltage to cause the digital output to change

TEMP

. Then calculate the

TEMP

−30)) + 1.8015V (1)

(2)

LM26-_ _B

LM26-_ _D

10132313

10132315

3.
A.

Observe that OS

B.

Drive V
C.
D.
E.

TEMP

Observe that OS is now low.

Release the V

Observe that OS is now high.

is high.

to ground.

pin.

TEMP

4.
A.

Observe that OS is high.

B.

Drive V

C.

When OS goes low, note the V

D.

V

TEMP

E.

Calculate Ttrig using Equation 2.

voltage down gradually.

TEMP

Trig = V

at OS trigger (HIGH->LOW)

TEMP

TEMP

voltage.

5.
A.

Gradually raise V
V

.

TEMP

B.

Calculate T

V

LOADING

TEMP

The V
40 µA sink). So care should be taken when attaching circuitry

output has very weak drive capability (1 µA source,

TEMP

HYST

to this pin. Capacitive loading may cause the V
oscillate. Simply adding a resistor in series as shown in Figure

TEMP

until OS

goes HIGH. Note

using Equation 2.

TEMP

output to

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 re­sistor. If an additional capacitive load is placed directly on the
LM26 output, rather than across C
a factor of 10 smaller than C

LOAD

, it should be at least

LOAD

.

5 www.national.com

TABLE 1. Resistive compensation for capacitive loading

LM26

C

LOAD

of V

TEMP

R (Ω)

≤100pF

1nF 8200

10nF 3000

100nF 1000

≥1µF

a) R in series with capacitor

b) R in series with signal path

FIGURE 2. Resistor placement for capacitive loading

NOISE CONSIDERATIONS

The LM26 has excellent power supply noise rejection. Listed
below is a variety of signals used to test the LM26 power sup­ply 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.

compensation of V

430

TEMP

0

10132317

10132318

mented to a surface. The temperature that the LM26 is sens­ing 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 temper­ature between the surface temperature and the air tempera­ture.

To ensure good thermal conductivity, the backside of the
LM26 die is directly attached to the GND pin (pin 2). The tem­peratures 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 conden­sation 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 pa­rameter used to calculate the rise of a part's junction temper­ature 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, I
on the V
and IDO is the load current on the digital output. Since the

output, VDO is the voltage on the digital output,

TEMP

is the load current

L_TEMP

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 resis­tance for different conditions and the rise in die temperature
of the LM26 without any loading on V
resistor on an open-drain digital output with a 5.5V power

and a 10k pull-up

TEMP

supply.

SOT23-5

no heat sink

θ

JA

(°C/W)

TJ−T

(°C)

A

SOT23-5

small heat sink

θ

JA

(°C/W)

TJ−T

(°C)

A

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)

MOUNTING CONSIDERATIONS

The LM26 can be applied easily in the same way as other
integrated-circuit temperature sensors. It can be glued or ce-

www.national.com 6

Typical Applications

LM26

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.

10132303

FIGURE 4. Two Speed Fan Speed Control

10132320

FIGURE 5. Fan High Side Drive

FIGURE 6. Fan Low Side Drive

7 www.national.com

10132321

LM26

10132322

FIGURE 7. Audio Power Amplifier Thermal Protection

FIGURE 8. Simple Thermostat

10132323

www.national.com 8

Physical Dimensions inches (millimeters) unless otherwise noted

LM26

5-Lead Molded SOT-23 Plastic Package, JEDEC

Order Number LM26CIM5 or LM26CIM5X

NS Package Number MA05B

9 www.national.com

Notes

For more National Semiconductor product information and proven design tools, visit the following Web sites at:

Products Design Support

Amplifiers www.national.com/amplifiers WEBENCH www.national.com/webench

Audio www.national.com/audio Analog University www.national.com/AU

Clock Conditioners www.national.com/timing App Notes www.national.com/appnotes

Data Converters www.national.com/adc Distributors www.national.com/contacts

Displays www.national.com/displays Green Compliance www.national.com/quality/green

Ethernet www.national.com/ethernet Packaging www.national.com/packaging

Interface www.national.com/interface Quality and Reliability www.national.com/quality

LVDS www.national.com/lvds Reference Designs www.national.com/refdesigns

Power Management www.national.com/power Feedback www.national.com/feedback

Switching Regulators www.national.com/switchers

LDOs www.national.com/ldo

LED Lighting www.national.com/led

PowerWise www.national.com/powerwise

Serial Digital Interface (SDI) www.national.com/sdi

Temperature Sensors www.national.com/tempsensors

Wireless (PLL/VCO) www.national.com/wireless

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LM26 SOT-23, ±3°C Accurate, Factory Preset Thermostat

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