National semiconductor Lm26 series User manual

LM26

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, tem-

perature sensor and comparator. Utilizing factory program-

ming, it can be manufactured with different trip points as well

as different digital output functionality. The trip point (T

OS

)

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

TEMP

). The digital output stage can be

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 tem-

perature shutdown event (OS or OS) or an under tempera-

ture shutdown event (US or US). When preset as an over-

temperature shutdown (OS) it will go LOW to indicate that

the die temperature is over the internally preset T

OS

and go

HIGH when the temperature goes below (T

OS

–T

HYST

). Simi-

larly, when preprogrammed as an undertemperature shut-

down (US) it will go HIGH to indicate that the temperature is

below T

US

and go LOW when the temperature is above

(T

US

+T

HYST

). The typical hysteresis, T

HYST

, can be set to

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

V

TEMP

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 Dis-

tributor or Sales Representative for information on minimum

order qualification. The LM26 is currently available in a

5-lead SOT-23 package.

Applications

nMicroprocessor Thermal Management

nAppliances

nPortable Battery Powered Systems

nFan Control

nIndustrial Process Control

nHVAC Systems

nRemote Temperature Sensing

nElectronic System Protection

Features

nInternal comparator with pin programmable 2˚C or 10˚C

hysteresis

nNo external components required

nOpen Drain or push-pull digital output; supports CMOS

logic levels

nInternal temperature sensor with V

TEMP

output pin

nV

TEMP

output allows after-assembly system testing

nInternal voltage reference and DAC for trip-point setting

nCurrently available in 5-pin SOT-23 plastic package

nExcellent power supply noise rejection

Key Specifications

jPower Supply Voltage 2.7V to 5.5V

jPower Supply Current 40µA(max)

20µA(typ)

jHysteresis 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.

May 2001

LM26 SOT-23,

±

3˚C Accurate, Factory Preset Thermostat

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Ordering Information

For more detailed information on the suffix meaning see the part number template at the end of the Electrical Characteris-

tics Section. Contact National Semiconductor for other set points and output options.

Order Number

Top Mark

NS Package

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

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-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 Description

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

3V

TEMP

Analog output voltage

proportional to temperature

Leave floating or connect to a high impedance

node.

4V

+

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

For PSRR information see Section Titled

NOISE CONSIDERATIONS.

5OS

Overtemperature Shutdown

open-drain active low

thermostat digital output

Controller interrupt, system or power supply

shutdown; pull-up resistor ≥10kΩ

OS Overtemperature Shutdown

totem-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

totem-pull active high

thermostat digital output

System or power supply shutdown

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

LM26

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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 T

A

= 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 T

MIN

≤T

A

≤T

MAX

LM26CIM −55˚C ≤T

A

≤+125˚C

Positive Supply Voltage (V

+

) +2.7V to +5.5V

Maximum V

OUT

+5.5V

LM26 Electrical Characteristics

The following specifications apply for V

+

= 2.7V

DC

to 5.5V

DC

, and V

TEMP

load current = 0µA unless otherwise specified. Bold-

face limits apply for T

A

=T

J

=T

MIN

to T

MAX

;all other limits T

A

=T

J

= 25˚C unless otherwise specified.

Typical LM26CIM Units

Symbol Parameter Conditions (Note 6) Limits (Limits)

(Note 7)

Temperature Sensor

Trip Point Accuracy (Includes

V

REF

, DAC, Comparator Offset,

and Temperature Sensitivity

errors)

-55˚C ≤T

A

≤+110˚C ±3 ˚C (max)

+120˚C ±4 ˚C (max)

Trip Point Hysteresis HYST = GND 11 ˚C

HYST = V

+

2˚C

V

TEMP

Output Temperature

Sensitivity −10.82 mV/˚C

V

TEMP

Temperature Sensitivity

Error to Equation:

V

O

= (−3.479x10

−6

x(T−30)

2

)

+ (−1.082x10

−2

x(T−30)) +

1.8015V

−30˚C ≤T

A

≤120˚C,

2.7V ≤V

+

≤5.5V

±3˚C (max)

−55˚C ≤T

A

≤120˚C,

4.5V ≤V

+

≤5.5V

±3˚C (max)

T

A

= 30˚C ±2.5 ˚C (max)

V

TEMP

Load Regulation −1µA ≤I

L

≤0 0.070 mV

0≤I

L

≤+40µA 0.7 mV (max)

V

TEMP

Line Regulation +2.7V ≤V

+

≤+5.5V,

−30˚C ≤T

A

≤

+120˚C

−0.2 mV/V

I

S

Supply Current 16 20

40

µA (max)

Digital Output and Input

I

OUT(“1”)

Logical “1” Output Leakage

Current (Note 9)

V

+

= +5.0V 0.001 1 µA (max)

V

OUT(“0”)

Logical “0” Output Voltage I

OUT

= +1.2mA and

V

+

≥2.7V;

I

OUT

= +3.2mA and

V

+

≥4.5V; (Note 8)

0.4 V (max)

V

OUT(“1”)

Logical “1” Push-Pull Output

Voltage

I

SOURCE

= 500µA,

V

+

≥2.7V

0.8xV

+

V (min)

I

SOURCE

= 800µA,

V

+

≥4.5V

V

+

− 1.5 V (min)

V

IH

HYST Input Logical ”1“ Threshold

Voltage

0.8xV

+

V (min)

V

IL

HYST Input Logical ”0“ Threshold

Voltage

0.2xV

+

V (max)

LM26

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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=(T

Jmax–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 θ

JA

SOT23-5, MA05B 250˚C/W

Note 4: The human body model is a 100pF capacitor discharge through a 1.5kΩresistor 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=T

A= 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

HH 0

JJ 1

KK 2

LL 3

x (10x) y (1x) Temperature (˚C)

NN 4

PP 5

RR 6

SS 7

TT 8

VV 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 T

OS

= 85˚C, and programmed as an active-low open-drain overtemperature shutdown

output.

•the part number LM26CIM5-FPD has T

US

= −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 informa-

tion.

LM26

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Functional Description

LM26 OPTIONS

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

TEMP

output allows after-assembly PCB testing

by following a simple test procedure. Simply measuring the

V

TEMP

output voltage will verify that the LM26 has been

assembled properly and that its temperature sensing cir-

cuitry is functional. The V

TEMP

output has very weak drive

capability that can be overdriven by 1.5mA. Therefore, one

can simply force the V

TEMP

voltage to cause the digital

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

+

and measure V

TEMP

. Then calculate the

temperature reading of the LM26 using the equation:

V

O

= (−3.479x10

−6

x(T−30)

2

) + (−1.082x10

−2

x(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 tem-

perature (reference temperature) should be measured

using an extremely accurate calibrated temperature sen-

sor.

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

TEMP

voltage down gradually.

C. When OS goes low, note the V

TEMP

voltage.

D. V

TEMP

Trig=V

TEMP

at OS trigger (HIGH->LOW)

E. Calculate Ttrig using Equation (2).

5.

A. Gradually raise V

TEMP

until OS goes HIGH. Note

V

TEMP

.

B. Calculate T

HYST

using Equation (2).

V

TEMP

LOADING

The V

TEMP

output has very weak drive capability (40µA

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

C

LOAD

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

C

LOAD

.

10132312

LM26-_ _A

10132313

LM26-_ _B

10132314

LM26-_ _C

10132315

LM26-_ _D

FIGURE 1. Output Pin Options Block Diagrams

LM26

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Applications Hints (Continued)

TABLE 1. Resistive compensation for capacitive

loading of V

TEMP

C

LOAD

R(Ω)

≤100pF 0

1nF 8200

10nF 3000

100nF 1000

≥1µF 430

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 ob-

served 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

cemented to a surface. The temperature that the LM26 is

sensing will be within about +0.06˚C of the surface tempera-

ture 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 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 connec-

tions.

The junction to ambient thermal resistance (θ

JA

) is the pa-

rameter used to calculate the rise of a part’s junction tem-

perature due to its power dissipation. For the LM26 the

equation used to calculate the rise in the die junction tem-

perature is as follows:

(3)

where T

A

is the ambient temperature, V

+

is the power supply

voltage, I

Q

is the quiescent current, I

L_TEMP

is the load

current on the V

TEMP

output, V

DO

is the voltage on the digital

output, and I

DO

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 V

TEMP

and a 10k pull-up

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

supply.

10132317

a) R in series with capacitor

10132318

b) R in series with signal path

FIGURE 2. Resistor placement for capacitive loading

compensation of V

TEMP

SOT23-5

no heat sink

SOT23-5

small heat sink

θ

JA

(˚C/W)

T

J

−T

A

(˚C)

θ

JA

(˚C/W)

T

J

−T

A

(˚C)

Still Air 250 0.11 TBD TBD

Moving Air TBD TBD TBD TBD

FIGURE 3. Thermal resistance (θ

JA

) and temperature

rise due to self heating (T

J

−T

A

)

LM26

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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

LM26

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Typical Applications (Continued)

10132322

FIGURE 7. Audio Power Amplifier Thermal Protection

10132323

FIGURE 8. Simple Thermostat

LM26

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Physical Dimensions inches (millimeters) unless otherwise noted

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

labeling, can be reasonably expected to result in a

significant injury to the user.

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.

National Semiconductor

Americas Customer

Support Center

Email: [email protected]

Tel: 1-800-272-9959

National Semiconductor

Europe Customer Support Center

Fax: +49 (0) 180-530 85 86

Email: [email protected]

Deutsch Tel: +49 (0) 69 9508 6208

English Tel: +44 (0) 870 24 0 2171

Français Tel: +33 (0) 1 41 91 8790

National Semiconductor

Asia Pacific Customer

Support Center

Email: [email protected]

National Semiconductor

Japan Customer Support Center

Fax: 81-3-5639-7507

Email: [email protected]

Tel: 81-3-5639-7560

www.national.com

LM26 SOT-23,

±

3˚C Accurate, Factory Preset Thermostat

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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National Semiconductor LM26 Series User manual

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