Rainbow Electronics LM26 User Manual

LM26

LM26 SOT-23,

June 2004

SOT-23,

±

3˚C Accurate, Factory Preset Thermostat

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 (T
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 (V
preset as either 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 TOSand go
HIGH when the temperature goes below (T
larly, when preprogrammed as an undertemperature shut­down (US) it will go HIGH to indicate that the temperature is
below T
(T

US+THYST

2˚C or 10˚C and is controlled by the state of the HYST pin. A
V

TEMP

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.

and go LOW when the temperature is above

US

). The typical hysteresis, T

analog output provides a voltage that is proportional

). The digital output stage can be

TEMP

OS–THYST

, can be set to

HYST

OS

). Simi-

Applications

n Microprocessor Thermal Management
n Appliances

n Portable Battery Powered Systems
n Fan Control
n Industrial Process Control
n HVAC Systems
n Remote Temperature Sensing
n Electronic System Protection

)

Features

n Internal comparator with pin programmable 2˚C or 10˚C

hysteresis

n No external components required
n Open Drain or push-pull digital output; supports CMOS

logic levels

n Internal temperature sensor with V
n V
n Internal voltage reference and DAC for trip-point setting
n Currently available in 5-pin SOT-23 plastic package
n Excellent power supply noise rejection

output allows after-assembly system testing

TEMP

TEMP

output pin

Key Specifications

j

Power Supply Voltage 2.7V to 5.5V

j

Power Supply Current 40µA(max)

j

Hysteresis Temperature 2˚C or 10˚C(typ)

Temperature Trip Point Accuracy

Temperature Range LM26CIM

−55˚C to +110˚C

+120˚C

±

3˚C (max)

±

4˚C (max)

±

3˚C Accurate, Factory Preset Thermostat

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.

© 2004 National Semiconductor Corporation DS101323 www.national.com

10132301

Ordering Information

LM26

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

LM26CIM5-KLA LM26CIM5X-KLA TKLA MA05B 23˚C Open Drain OS

LM26CIM5-NPA LM26CIM5X-NPA TNPA MA05B 45˚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

NS Package

Number Trip Point Setting Output FunctionBulk Rail 3000 Units in Tape & Reel

Connection Diagram

10132302

Pin Description

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

3V

4V+Supply input 2.7V to 5.5V with a 0.1µF bypass capacitor. For

5OS

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

Pin

Name

the die through lead frame.

TEMP

OS Overtemperature Shutdown push-pull

US

US Undertemperature Shutdown push-pull

Analog output voltage proportional to
temperature

Overtemperature Shutdown open-drain
active low thermostat digital output

active high thermostat digital output

Undertemperature Shutdown open-drain
active low thermostat digital output

active high thermostat digital output

Function Connection

System GND

Leave floating or connect to a high impedance
node.

PSRR 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

ESD Susceptibility (Note 4)

Human Body Model
Machine Model

2500V

Package Input Current(Note 2) 20mA

Package Dissipation at T

= 25˚C

A

(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 T

LM26CIM −55˚C ≤ TA≤ +125˚C

Positive Supply Voltage (V

Maximum V

OUT

+

) +2.7V to +5.5V

MIN

≤ TA≤ T

Storage Temperature −65˚C to + 150˚C

LM26 Electrical Characteristics

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

face limits apply for T

A=TJ=TMIN

to T

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

MAX

Symbol Parameter Conditions (Note 6) Limits (Limits)

Temperature Sensor

Trip Point Accuracy (Includes
V

, DAC, Comparator Offset,

REF

and Temperature Sensitivity

-55˚C ≤ T

+120˚C

≤ +110˚C

A

errors)

Trip Point Hysteresis HYST = GND 11 ˚C

+

V

Output Temperature

TEMP

HYST = V

Sensitivity

Temperature Sensitivity

V

TEMP

Error to Equation:

= (−3.479x10−6x(T−30)2)

V

O

+ (−1.082x10−2x(T−30)) +

1.8015V

V

Load Regulation −1µA ≤ IL≤ 0 0.070 mV

TEMP

V

Line Regulation +2.7V ≤ V+≤ +5.5V,

TEMP

−30˚C ≤ T

2.7V ≤ V

−55˚C ≤ T

4.5V ≤ V

A

+

≤ 5.5V

A

+

≤ 5.5V

≤ 120˚C,

≤ 120˚C,

TA= 30˚C

0 ≤ I

≤ +40µA 0.7 mV (max)

L

−30˚C ≤ T

≤

A

+120˚C

I

S

Supply Current 16 20

Digital Output and Input

I

OUT(“1”)

Logical “1” Output Leakage

V+= +5.0V 0.001 1 µA (max)

Current (Note 9)

V

OUT(“0”)

V

OUT(“1”)

Logical “0” Output Voltage I

Logical “1” Push-Pull Output
Voltage

V

IH

HYST Input Logical ”1“ Threshold

= +1.2mA and

OUT

+

≥2.7V;

V

= +3.2mA and

I

OUT

+

≥4.5V; (Note 8)

V

I

SOURCE

V

I

SOURCE

V

+

≥ 2.7V

+

≥4.5V

= 500µA,

= 800µA,

Voltage

V

IL

HYST Input Logical ”0“ Threshold
Voltage

load current = 0µA unless otherwise specified. Bold-

TEMP

Typical LM26CIM Units

(Note 7)

±

3 ˚C (max)

±

4 ˚C (max)

2˚C

−10.82 mV/˚C

±

3 ˚C (max)

±

3 ˚C (max)

±

2.5 ˚C (max)

−0.2 mV/V

40

0.4 V (max)

+

0.8xV

+

V

− 1.5 V (min)

+

0.8xV

+

0.2xV

µA (max)
µA (max)

V (min)

V (min)

V (max)

250V

MAX

+5.5V

www.national.com3

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 (V
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 T
given in the Absolute Maximum Ratings, whichever is lower. For this device, T
package types when board mounted follow:

) at any pin exceeds the power supply (V

I

(ambient temperature). The maximum allowable power dissipation at any temperature is PD=(T

A

I

<

Jmax

GND or V

Package Type θ

>

V+), the current at that pin should be limited to 5mA. The 20mA

I

(maximum junction temperature), θJA(junction to

Jmax

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

JA

)/θJAor the number

Jmax–TA

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 T

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
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.

OUT

= 25˚C and represent most likely parametric norm.

J=TA

=3.2mA and V

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

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

HH 0

JJ 1

KK 2

x (10x) y (1x) Temperature (˚C)

NN 4

PP 5

RR 6

SS 7

TT 8

VV 9

X- 10

Y- 11

Z- 12

LL 3

The value of z describes the assignment/function of the output as shown in the following table:

Open-Drain/

Active-Low/High

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

Functional Description

LM26 OPTIONS

LM26

LM26-_ _A

10132312

LM26-_ _C

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

output voltage will verify that the LM26 has been

V

TEMP

assembled properly and that its temperature sensing cir­cuitry is functional. The V
capability that can be overdriven by 1.5mA. Therefore, one
can simply force the V
output to change 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
temperature reading of the LM26 using the equation:

= (−3.479x10−6x(T−30)2) + (−1.082x10−2x(T−30)) +

V

O

or

2. Verify that the temperature measured in step one is
within (
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

TEMP

voltage to cause the digital

TEMP

+

and measure V

. Then calculate the

TEMP

1.8015V (1)

±

3˚C + error of reference temperature sensor) of

(2)

LM26-_ _B

10132313

LM26-_ _D

10132315

3.
A. Observe that OS is high.
B. Drive V

TEMP

to ground.
C. Observe that OS is now low.
D. Release the V

TEMP

pin.

E. Observe that OS is now high.

4.
A. Observe that OS is high.
B. Drive V
C. When OS goes low, note the V
D. V

TEMP

voltage down gradually.

TEMP

Trig=V

at OS trigger (HIGH->LOW)

TEMP

TEMP

voltage.

E. Calculate Ttrig using Equation (2).

5.
A. Gradually raise V

V

.

TEMP

B. Calculate T

V

LOADING

TEMP

The V

output has very weak drive capability (40µA

TEMP

HYST

until OS goes HIGH. Note

TEMP

using Equation (2).

source, 1µA sink). So care should be taken when attaching
circuitry to this pin. Capacitive loading may cause the V

TEMP

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 resistor. If an additional capacitive load is
placed directly on the LM26 output, rather than across

, it should be at least a factor of 10 smaller than

C

LOAD

.

C

LOAD

www.national.com5

Applications Hints (Continued)

LM26

TABLE 1. Resistive compensation for capacitive

C

loading of V

LOAD

TEMP

R(Ω)

≤100pF 0

1nF 8200

10nF 3000

100nF 1000

≥1µF 430

a) R in series with capacitor

b) R in series with signal path

FIGURE 2. Resistor placement for capacitive loading

compensation of V

TEMP

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.

10132317

10132318

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 (θ

) is the pa-

JA

rameter 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 T
voltage, I
current on the V
output, and I

is the ambient temperature, V+is the power supply

A

is the quiescent current, I

Q

DO

output, VDOis the voltage on the digital

TEMP

is the load current on the digital output. Since

L_TEMP

is the load

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 resis­tance for different conditions and the rise in die temperature
of the LM26 without any loading on V

and a 10k pull-up

TEMP

resistor on an open-drain digital output with a 5.5V power
supply.

SOT23-5

no heat sink

θ

JA

(˚C/W)

T

J−TA

(˚C)

SOT23-5

small heat sink

θ

JA

T

(˚C/W)

J−TA

(˚C)

Still Air 250 0.11 TBD TBD

Moving Air TBD TBD TBD TBD

FIGURE 3. Thermal resistance (θ

rise due to self heating (T

) and temperature

JA

J−TA

)

MOUNTING CONSIDERATIONS

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

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

10132321

www.national.com7

Typical Applications (Continued)

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 SOT-23,

±

3˚C Accurate, Factory Preset Thermostat

5-Lead Molded SOT-23 Plastic Package, JEDEC

Order Number LM26CIM5 or LM26CIM5X

NS Package Number MA05B

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.

BANNED SUBSTANCE COMPLIANCE

National Semiconductor certifies that the products and packing materials meet the provisions of the Customer Products
Stewardship Specification (CSP-9-111C2) and the Banned Substances and Materials of Interest Specification
(CSP-9-111S2) and contain no ‘‘Banned Substances’’ as defined in CSP-9-111S2.

National Semiconductor
Americas Customer
Support Center

Email: [e-mail]
Tel: [phone]

www.national.com

National Semiconductor
Europe Customer Support Center

Fax: [phone]

Email: [e-mail]
Deutsch Tel: [phone]
English Tel: [phone]
Français Tel: [phone]

National Semiconductor
Asia Pacific Customer
Support Center

Email: [e-mail]

National Semiconductor
Japan Customer Support Center

Fax: [phone]
Email: [e-mail]
Tel: [phone]

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.