LM26
SOT-23,
3C 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 -55C to +110C in 1C 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
2C or 10C 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
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 2C or 10C
hysteresis
n
No external components required
n
Open Drain or push-pull digital output; supports CMOS
logic levels
n
Internal temperature sensor with V
TEMP
output pin
n
V
TEMP
output allows after-assembly system testing
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
Key Specifications
j
Power Supply Voltage
2.7V to 5.5V
j
Power Supply Current
40A(max)
20A(typ)
j
Hysteresis Temperature
2C or 10C(typ)
Temperature Trip Point Accuracy
Temperature Range
LM26CIM
-55C to +110C
3C (max)
+120C
4C (max)
LM26CIM5-TPA Simplified Block Diagram and Connection Diagram
10132301
The LM26CIM5-TPA has a fixed trip point of 85C.
For other trip point and output function availability,
please see ordering information or contact National Semiconductor.
March 2005
LM26
SOT
-23,
3C
Accurate,
Factory
Preset
Thermostat
2005 National Semiconductor Corporation
DS101323
www.national.com
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 Function
Bulk Rail
3000 Units in Tape & Reel
LM26CIM5-NPA
LM26CIM5X-NPA
TNPA
MA05B
45C
Open Drain OS
LM26CIM5-PHA
LM26CIM5X-PHA
TPHA
MA05B
50C
Open Drain OS
LM26CIM5-RPA
LM26CIM5X-RPA
TRPA
MA05B
65C
Open Drain OS
LM26CIM5-SHA
LM26CIM5X-SHA
TSHA
MA05B
70C
Open Drain OS
LM26CIM5-SPA
LM26CIM5X-SPA
TSPA
MA05B
75C
Open Drain OS
LM26CIM5-TPA
LM26CIM5X-TPA
TTPA
MA05B
85C
Open Drain OS
LM26CIM5-VHA
LM26CIM5X-VHA
TVHA
MA05B
90C
Open Drain OS
LM26CIM5-VPA
LM26CIM5X-VPA
TVPA
MA05B
95C
Open Drain OS
LM26CIM5-XHA
LM26CIM5X-XHA
TXHA
MA05B
100C
Open Drain OS
LM26CIM5-XPA
LM26CIM5X-XPA
TXPA
MA05B
105C
Open Drain OS
LM26CIM5-YHA
LM26CIM5X-YHA
TYHA
MA05B
110C
Open Drain OS
LM26CIM5-YPA
LM26CIM5X-YPA
TYPA
MA05B
115C
Open Drain OS
LM26CIM5-ZHA
LM26CIM5X-ZHA
TZHA
MA05B
120C
Open Drain OS
Connection Diagram
10132302
Pin Description
Pin
Number
Pin
Name
Function
Connection
1
HYST
Hysteresis control, digital input
GND for 10C or V
+
for 2C
2
GND
Ground, connected to the back side of
the die through lead frame.
System GND
3
V
TEMP
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 0.1F 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
10k
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
10k
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.
LM26
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2
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
= 25C
(Note 3)
500mW
Soldering Information
SOT23 Package
Vapor Phase (60 seconds)
Infrared (15 seconds)
215C
220C
Storage Temperature
-65C to + 150C
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
-55C
T
A
+125C
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 = 0A unless otherwise specified. Bold-
face limits apply for T
A
= T
J
= T
MIN
to T
MAX
; all other limits T
A
= T
J
= 25C 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)
-55C
T
A
+110C
3
C (max)
+120C
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
-30C
T
A
120C,
2.7V
V
+
5.5V
3
C (max)
-55C
T
A
120C,
4.5V
V
+
5.5V
3
C (max)
T
A
= 30C
2.5
C (max)
V
TEMP
Load Regulation
-1A
I
L
0
0.070
mV
0
I
L
+40A
0.7
mV (max)
V
TEMP
Line Regulation
+2.7V
V
+
+5.5V,
-30C
T
A
+120C
-0.2
mV/V
I
S
Supply Current
16
20
40
A (max)
A (max)
Digital Output and Input
I
OUT("1")
Logical "1" Output Leakage
Current (Note 9)
V
+
= +5.0V
0.001
1
A (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
= 500A,
V
+
2.7V
0.8 x V
+
V (min)
I
SOURCE
= 800A,
V
+
4.5V
V
+
- 1.5
V (min)
V
IH
HYST Input Logical "1" Threshold
Voltage
0.8 x V
+
V (min)
V
IL
HYST Input Logical "0" Threshold
Voltage
0.2 x V
+
V (max)
LM26
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3
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 (V
I
) at any pin exceeds the power supply (V
I
<
GND or V
I
>
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
Jmax
(maximum junction temperature),
JA
(junction to
ambient thermal resistance) and T
A
(ambient temperature). The maximum allowable power dissipation at any temperature is P
D
= (T
Jmax
T
A
)/
JA
or the number
given in the Absolute Maximum Ratings, whichever is lower. For this device, T
Jmax
= 150C. For this device the typical thermal resistance (
JA
) of the different
package types when board mounted follow:
Package Type
JA
SOT23-5, MA05B
250C/W
Note 4: The human body model is a 100pF capacitor discharge through a 1.5k
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
J
= T
A
= 25C 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
OUT
=3.2mA and V
OUT
=0.4V. With a thermal resistance of 250C/W, this power dissipation would cause an increase in the die temperature of
about 0.32C due to self heating. Self heating is not included in the trip point accuracy specification.
Note 9: The 1A 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 15C
increase in temperature. For example, the 1nA typical current at 25C would increase to 16nA at 85C.
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 T
OS
= 85C, and programmed as an active-low open-drain overtemperature shutdown
output.
the part number LM26CIM5-FPD has T
US
= -5C, 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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4
Functional Description
LM26 OPTIONS
The LM26 can be factory programmed to have a trip point
anywhere in the range of -55C to +110C.
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 85C 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 (
3C + 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 (40A
source, 1A 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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5
Applications Hints
(Continued)
TABLE 1. Resistive compensation for capacitive
loading of V
TEMP
C
LOAD
R (
)
100pF
0
1nF
8200
10nF
3000
100nF
1000
1F
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 +0.06C 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 (
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
JA
(C/W)
T
J
-T
A
(C)
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 (
JA
) and temperature
rise due to self heating (T
J
-T
A
)
LM26
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6
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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7
Typical Applications
(Continued)
10132322
FIGURE 7. Audio Power Amplifier Thermal Protection
10132323
FIGURE 8. Simple Thermostat
LM26
www.national.com
8
Physical Dimensions
inches (millimeters) unless otherwise noted
5-Lead Molded SOT-23 Plastic Package, JEDEC
Order Number LM26CIM5 or LM26CIM5X
NS Package Number MA05B
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.
For the most current product information visit us at www.national.com.
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.
BANNED SUBSTANCE COMPLIANCE
National Semiconductor manufactures products and uses packing materials that 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.
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LM26
SOT
-23,
3C
Accurate,
Factory
Preset
Thermostat
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