Rainbow Electronics LM27 User Manual

LM27

LM27 SOT-23,

August 2002

SOT-23,

±

3˚C Accurate, 120˚C-150˚C Factory Preset

Thermostat

General Description

The LM27 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 +120˚C to +150˚C in 1˚C increments. The LM27 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 −10.7mV/˚C output slope.
Currently, there are several standard parts available, see

ordering information for details. For other part options, con­tact a National Semiconductor Distributor or Sales Repre­sentative for information on minimum order qualification. The
LM27 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-

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

)

Features

n Internal comparator with pin selectable 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)

j

Temperature Trip Point Accuracy

±

±

3˚C Accurate, 120˚C-150˚C Factory Preset Thermostat

15µA(typ)

3˚C (max)

Applications

n Microprocessor Thermal Management
n Appliances

LM27CIM5-2HJ Simplified Block Diagram and Connection Diagram

The LM27CIM5-2HJ has a fixed trip point of 140˚C.

For other trip point and output function availability,

please see ordering information or contact National Semiconductor.

© 2002 National Semiconductor Corporation DS200307 www.national.com

20030701

Ordering Information

LM27

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

LM27CIM5-1HJ LM27CIM5X-1HJ T1HJ MA05B 130˚C Open Drain OS

LM27CIM5-2HJ LM27CIM5X-2HJ T2HJ MA05B 140˚C Open Drain OS

NS Package

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

Connection Diagram

20030702

Pin Description

Pin Number Pin Name Function Connection

1 HYST Hysteresis control, digital

input

2 GND Ground, connected to the

back side of the die through
lead frame.

3V

4V

5OS

TEMP

+

OS Overtemperature Shutdown

US

US Undertemperature Shutdown

Analog output voltage
proportional to temperature

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

Overtemperature Shutdown
open-drain active low
thermostat digital output

totem-pull active high
thermostat digital output

Undertemperature Shutdown
open-drain active low
thermostat digital output

totem-pull active high
thermostat digital output

GND for 10˚C or V

System GND

Leave floating or connect to a high impedance
node.

For 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

+

for 2˚C

Note: pin 5 functionality and trip point setting are programmed during LM27 manufacture.

www.national.com 2

LM27

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

(Note 3) 500mW

Soldering Information

SOT23 Package

Vapor Phase (60 seconds)
Infrared (15 seconds)

= 25˚C

A

215˚C
220˚C

Storage Temperature −65˚C to + 150˚C

ESD Susceptibility (Note 4)

Human Body Model

2500V

Machine Model

Operating Ratings(Note 1)

Specified Temperature Range T

LM27CIM −40˚C ≤ TA≤ +150˚C

Positive Supply Voltage (V

Maximum V

OUT

+

) +2.7V to +5.5V

MIN

≤ TA≤ T

LM27 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

+120˚C

<

T

A

and Temperature Sensitivity
errors)

Trip Point Hysteresis HYST = GND 10 ˚C

+

V

Output Temperature

TEMP

HYST = V

Sensitivity

Temperature Sensitivity

V

TEMP

Error to Equation:

= (−3.552x10−6x(T−30)2+

V

O

(−10.695x10−3x(T−30))+

1.8386V

V

Load Regulation −1µA ≤ IL≤ 0 0.070 mV

TEMP

V

Line Regulation +2.7V ≤ V+≤ +5.5V,

TEMP

I

S

Supply Current 15 22

−30˚C ≤ T

2.7V ≤ V

A

+

≤ 5.5V

≤ 150˚C,

−55˚C ≤ TA≤ 150˚C,

+

4.5V ≤ V

T

A

0 ≤ I

−30˚C ≤ T

≤ 5.5V

= 25˚C

≤ +40µA 0.7 mV (max)

L

≤ +120˚C

A

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

= 500µA, V

≥ 2.7V

I

SOURCE

V

+

≥4.5V

= 800µA,

Voltage

V

IL

HYST Input Logical ”0“ Threshold
Voltage

load current = 0µA unless otherwise specified. Bold-

TEMP

Typical LM27CIM Units

(Note 7)

+150˚C

±

3 ˚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

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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

LM27

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 LM27 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 LM27CIM-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)

-H 0

-J 1

-K 2

-L 3

-N 4

-P 5

-R 6

x (10x) y (1x) Temperature (˚C)

-S 7

-T 8

-V 9

Z- 12

1- 13

2- 14

3- 15

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 J Active-Low, Open-Drain, OS output

0 0 1 K Active-Low, Open-Drain, US output

110LActive-High, Push-Pull, OS output

1 1 1 N Active-High, Push-Pull, US output

For example:

the part number LM27CIM5-2SJ has TOS= 147˚C, and programmed as an active-low open-drain overtemperature shutdown

•

output.
the part number LM27CIM5-ZLN has TUS= 123˚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

LM27 OPTIONS

LM27

LM27-_ _J

20030712

LM27-_ _L

20030714

FIGURE 1. Output Pin Options Block Diagrams

The LM27 can be factory programmed to have a trip point
anywhere in-between 120˚C to 150˚C.

Applications Hints

AFTER-ASSEMBLY PCB TESTING

The LM27’s V
by following a simple test procedure. Simply measuring the

output voltage will verify that the LM27 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
LM27CIM5X-2HJ which has a 140˚C trip point.

1. Turn on V
temperature reading of the LM27 using the equation:

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, which is in close proximity to and mounted on the
same PCB as the LM27 perhaps even touching the GND
lead of the LM27 if possible. The LM27 will sence the

output allows after-assembly PCB testing

TEMP

output has very weak drive

TEMP

voltage to cause the digital

TEMP

+

and measure V

= (−3.552x10−6x(T−30)2)+

V

O

(−10.69576x10

±

3˚C + error of reference temperature sensor) of

−3

x(T−30)) + 1.8386V (1)

. Then calculate the

TEMP

(2)

LM27-_ _K

20030713

LM27-_ _N

20030715

board temperature not the ambient temperature (see
Section Titled Mounting Considerations)

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 LM27 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)

LM27

TABLE 1. Resistive compensation for capacitive

loading of V

C

LOAD

≤100pF 0

1nF 8200

10nF 3000

100nF 1000

≥1µF 430

a) R in series with capacitor

TEMP

R(Ω)

20030717

MOUNTING CONSIDERATIONS

The LM27 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 LM27 is
sensing will be within about +0.06˚C of the surface tempera­ture to which the LM27’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
LM27 die is directly attached to the GND pin (pin 2). The
temperatures of the lands and traces to the other leads of the
LM27 will also affect the temperature that is being sensed.

Alternatively, the LM27 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 LM27 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 LM27 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 LM27 the
equation used to calculate the rise in the die junction tem­perature is as follows:

b) R in series with signal path

20030718

FIGURE 2. Resistor placement for capacitive loading

compensation of V

TEMP

NOISE CONSIDERATIONS

The LM27 has excellent power supply noise rejection. Listed
below is a variety of signals used to test the LM27 power
supply rejection. False triggering of the output was not ob­served when these signals where coupled into the V+ pin of
the LM27.

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
LM27 one degree centigrade way from the trip point with the
output not activated.

(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 LM27’s junction temperature is the actual temperature
being measured, care should be taken to minimize the load
current that the LM27 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 LM27 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

)

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Typical Applications

LM27

Note: The fan’s control pin has internal pull-up. The 10k pull-down sets a slow fan speed. When the output of the LM27 goes low, the fan will speed up.

20030703

FIGURE 4. Two Speed Fan Speed Control

20030720

FIGURE 5. Fan High Side Drive

FIGURE 6. Fan Low Side Drive

20030721

www.national.com7

Typical Applications (Continued)

LM27

20030722

FIGURE 7. Audio Power Amplifier Thermal Protection

FIGURE 8. Simple Thermostat

20030723

www.national.com 8

Physical Dimensions inches (millimeters)

unless otherwise noted

LM27 SOT-23,

±

3˚C Accurate, 120˚C-150˚C Factory Preset Thermostat

5-Lead Molded SOT-23 Plastic Package, JEDEC

Order Number LM27CIM5 or LM27CIM5X

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.

National Semiconductor
Corporation

Americas
Email: [e-mail]

www.national.com

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.

National Semiconductor
Europe

Fax: [phone]

Email: [e-mail]
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Response Group

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