TEXAS INSTRUMENTS LM 75 SMD Datasheet

LM75 I2C Digital Temperature Sensor and Thermal
Watchdog

February 1996

LM75 I

2

C Digital Temperature Sensor and Thermal Watchdog

General Description

The LM75 is a temperature sensor, Delta-Sigma analog-to­digital converter, and digital over-temperature detector with

2

I

C interface. The host can query the LM75 at any time to
read temperature. The open-drain Overtemperature Shut­down (O.S.) output becomes active when the temperature
exceeds a programmable limit. This pin can operate in ei­ther ‘‘Comparator’’ or ‘‘Interrupt’’ mode.

The host can program both the temperature alarm threshold
(T

) and the temperature at which the alarm condition

OS

goes away (T
contents of the LM75’s T
pins (A0, A1, A2) are available for I

). In addition, the host can read back the

HYST

OS

and T

HYST

2

C address selection.

registers. Three

The sensor powers up in Comparator mode with default
thresholds of 80

The LM75’s 3.0V to 5.5V supply voltage range, low supply
current, and I

CTOSand 75§CT

§

2

C interface make it ideal for a wide range of

HYST

.

applications. These include thermal management and pro­tection applications in personal computers, electronic test
equipment, and office electronics.

Simplified Block Diagram

Features

Y

Tiny SO-8 package saves space (SOT-8 under develop­ment)

Y

I2C Bus interface

Y

Separate open-drain output pin operates as interrupt or
comparator/thermostat output

Y

Register readback capability

Y

Power up defaults permit stand-alone operation as ther­mostat

Y

Shutdown mode to minimize power consumption

Y

Up to 8 LM75s can be connected to a single I2C bus

Key Specifications

Y

Supply Voltage 3.0V to 5.5V

Y

Supply Current operating 250 mA typ

1mAmax

shutdown 1 mA typ

Y

Temperature Accuracyb25§Cto100§Cg2§C(max)

b

55§Cto125§Cg3§C(max)

Applications

Y

System Thermal Management

Y

Personal Computers

Y

Office Electronics

Y

Electronic Test Equipment

C

1996 National Semiconductor Corporation RRD-B30M36/Printed in U. S. A.

TL/H/12658

TL/H/12658– 1

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Connection Diagrams

SO-8

TL/H/12658– 2

Order Number LM75CIM-3, LM75CIMX-3,

LM75CIM-5 or LM75CIMX-5

See NS Package Number M08A

Ordering Information

Order Number

LM75CIM-3 3.3V

LM75CIMX-3 3.3V 2500 Units on Tape and

LM75CIM-5 5V

LM75CIMX-5 5V 2500 Units on Tape and

Supply

Voltage

Supplied As

Reel

Reel

Pin Description

Label Pin

SDA 1 I2C Serial Bi-Directional Data Line From Controller

SCL 2 I2C Clock Input From Controller

O.S. 3 Overtemperature Shutdown Open Collector Output Pull Up Resistor, Controller Interrupt Line

GND 4 Power Supply Ground Ground

a

V

S

A0–A2 7,6,5 User-Set I2C Address Inputs Ground (Low, ‘‘0’’) oraVS(High, ‘‘1’’)

Ý

8 Positive Supply Voltage Input DC Voltage from 3V to 5.5V

Function Typical Connection

FIGURE 1. Typical Application

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TL/H/12658– 3

Absolute Maximum Ratings (Note 1)

b

Supply Voltage

Voltage at any Pin

b

Input Current at any Pin (Note 2) 5 mA

Package Input Current (Note 2) 20 mA

O.S. Output Sink Current 10 mA

O.S. Output Voltage 6.5V

Storage Temperature

Soldering Information, Lead Temperature
SO Package (Note 3)

Vapor Phase (60 seconds) 215
Infrared (15 seconds) 220

0.3V to 6.5V

0.3V toaV

b

65§Ctoa150§C

a

0.3V

S

ESD Susceptibility (Note 4)

Human Body Model 2.0 kV
Machine Model TBD

Operating Ratings

Specified Temperature Range T

(Note 5)

b

Supply Voltage Range (aVS)

C

§

C

§

to T

MIN

55§Ctoa125§C

a

3.0V toa5.5V

MAX

Temperature-to-Digital Converter Characteristics

Unless otherwise noted, these specifications apply foraV
(Note 6). Boldface limits apply for T

e

e

T

A

J

ea

5 Vdc for LM75CIM-5 andaV

S

T

to T

MIN

; all other limits T

MAX

e

A

Parameter Conditions Typical

Accuracy T

eb

A

eb

T

A

25§Ctoa100§C
55§Ctoa125§C

Resolution 9 Bits

Temperature Conversion Time (Note 8) 100 ms

Quiescent Current I2C Inactive 0.25 mA

2

I

C Active 1.0 mA (max)

Shutdown Mode 1 mA

O.S. Output Saturation Voltage I

e

4.0 mA 0.8

OUT

(Note 9)

O.S. Delay (Note 10) 1 Conversions (min)

TOSDefault Temperature (Note 11) 80

T

Default Temperature (Note 11) 75

HYST

Logic Electrical Characteristics

Unless otherwise noted, these specifications apply foraV

T

; all other limits T

MAX

e

ea

T

A

25 C, unless otherwise noted.

J

ea

5 Vdc. Boldface limits apply for T

S

DIGITAL DC CHARACTERISTICS

Symbol Parameter Conditions Typical

V

V

I

IN(1)

I

IN(0)

C

I

OH

V

t

OF

IN(1)

IN(0)

IN

OL

Logical ‘‘1’’ Input Voltage 2.0 V (min)

Logical ‘‘0’’ Input Voltage 0.8 V (max)

Logical ‘‘1’’ Input Current V

Logical ‘‘0’’ Input Current V

e

5V 0.005 1.0 mA (max)

IN

e

0V

IN

b

0.005

All Digital Inputs 20 pF

High Level Output Current V

Low Level Output Voltage I

Output Fall Time C

e

5V 100 mA (max)

OH

e

3mA 0.4 V (max)

OL

e

400 pF 250

L

e

I

3mA

O

ea

3.3 Vdc for LM75CIM-3

S

ea

T

25 C, unless otherwise noted.

J

Limits Units

(Note 7) (Limit)

g

2.0

g

3.0

C (max)

§

V (max)

6 Conversions (max)

§

§

e

e

T

A

J

Limits Units

(Note 7) (Limit)

b

1.0 mA (max)

C

C

T

MIN

ns (max)

to

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Logic Electrical Characteristics (Continued)

2

I

C DIGITAL SWITCHING CHARACTERISTICS

Unless otherwise noted, these specifications apply for
otherwise specified. Boldface limits apply for T
otherwise noted.

The switching characteristics of the LM75 fully meet or exceed the published specifications of the I
parameters are the timing relationships between SCL and SDA signals related to the LM75. They are not the I
tions.

Symbol Parameter Conditions Typical

t

1

t

2

t

3

t

4

t

5

SCL (Clock) Period 2.5 ms(min)

Data in Set-Up Time to SCL High 100 ns(min)

Data Out Stable after SCL Low 0 ns(min)

SDA Low Set-Up Time to SCL Low (Start Condition) 100 ns(min)

SDA High Hold Time after SCL High (Stop Condition) 100 ns(min)

a

ea

V

5 Vdc, CL(load capacitance) on output linese80 pF unless

S

e

e

T

T

A

J

MIN

to T

; all other limits T

MAX

e

T

A

2

C bus. The following

ea

25§C, unless

J

2

C bus specifica-

Limits Units

(Note 7) (Limit)

Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. DC and AC electrical specifications do not apply when operating

the device beyond its rated operating 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 5 mA to four.

Note 3: See AN-450
Semiconductor Linear Data Book for other methods of soldering surface mount devices.

Note 4: Human body model, 100 pF discharged through a 1.5 kX resistor. Machine model, 200 pF discharged directly into each pin.

Note 5: Thermal resistance of the SO-8 package is 200

Note 6: Both part numbers of the LM75 will operate properly over theaVSsupply voltage range of 3V to 5.5V. The devices are tested and specified for rated

accuracy at their nominal supply voltage. Accuracy will typically degrade 1

Note 7: Limits are guaranteed to National’s AOQL (Average Outgoing Quality Level).

Note 8: This specification is provided only to indicate how often temperature data is updated. The LM75 can be read at any time without regard to conversion state

(and will yield last conversion result). If a conversion is in process it will be interrupted and restarted after the end of the read.

Note 9: For best accuracy, minimize output loading. Higher sink currents can affect sensor accuracy with internal heating. This can cause an error of 0.64
rated sink current and saturation voltage based on junction-to-ambient thermal resistance.

Note 10: O.S. Delay is user programmable up to 6 ‘‘over limit’’ conversions before O.S. is set to minimize false tripping in noisy environments.

Note 11: Default values set at power up.

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‘‘Surface Mounting Methods and Their Effect on Product Reliability’’

) at any pin exceeds the power supplies (V

I

C/W, junction-to-ambient when attached to a printed circuit board with 2 oz. foil as shown in

§

k

I

C/V of variation inaVSas it varies from the nominal value.

§

GND or V

l

a

VS) the current at that pin should be limited to 5 mA. The 20 mA

I

or the section titled ‘‘Surface Mount’’ found in a current National

TL/H/12658– 4

Figure 3.

C at full

§

Electrical Characteristics (Continued)

FIGURE 2. Temperature-to-Digital Transfer Function (Non-linear scale for clarity)

TL/H/12658– 5

FIGURE 3. Printed Circuit Board Used for Thermal Resistance Specifications

TL/H/12658– 6

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1.0 Functional Description

The LM75 temperature sensor incorporates a band-gap
type temperature sensor and 9-bit ADC (Delta-Sigma Ana­log-to-Digital Converter). The temperature data output of the
LM75 is available at all times via the I
is in progress, it will be stopped and restarted after the read.
A digital comparator is also incorporated that compares a
series of readings, the number of which is user-selectable,
to user-programmable setpoint and hysteresis values. The
comparator trips the O.S. output line, which is programma­ble for mode and polarity.

In Comparator mode the O.S. Output behaves like a thermo­stat. The output becomes active when temperature exceeds
the T

limit, and leaves the active state when the tempera-

OS

ture drops below the T
put can be used to turn a cooling fan on, initiate an emer-

HYST

gency system shutdown, or reduce system clock speed.

In Interrupt mode exceeding T
O.S. will remain active indefinitely until reset by reading any
register via the I
by crossing T
by Temperature going below T

2

C interface. Once O.S. has been activated

, then reset, it can be activated again only

OS

active indefinitely until being reset by a read. Placing the
LM75 in shutdown mode also resets the O.S. Output.

2

C bus. If a conversion

limit. In this mode the O.S. out-

also makes O.S. active but

OS

. Again, it will remain

HYST

1.1 DEFAULT MODES

LM75 always powers up in a known state. LM75 power up
default conditions are:

1. Comparator mode

2. T

set to 80§C

OS

3. T

set to 75§C

HYST

4. O.S. active low

5. Pointer set to ‘‘00’’; Temperature Register

With these operating conditions LM75 can act as a stand­alone thermostat with the above temperature settings. Con­nection to an I

2

1.2 I

2

C bus is not required.

C BUS INTERFACE

The LM75 operates as a slave on the I2C bus, so the SCL
line is an input (no clock is generated by the LM75) and the
SDA line is a bi-directional serial data path. According to I

2

bus specifications, the LM75 has a 7-bit slave address. The
four most significant bits of the slave address are hard wired
inside the LM75 and are ‘‘1001’’. The three least significant
bits of the address are assigned to pins A2 –A0, and are set
by connecting these pins to ground for a low, (0); or to

a

V

for a high, (1).

C

S

*Note: These interrupt mode resets of O.S. occur only when LM75 is read. Otherwise, O.S. would remain active indefinitely for any event.

FIGURE 4. O.S. Output Temperature Response Diagram

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TL/H/12658– 7

1.0 Functional Description (Continued)

Therefore, the complete slave address is:

1 0 0 1 A2 A1 A0

MSB LSB

1.3 TEMPERATURE DATA FORMAT

Temperature data can be read from the Temperature, T
Set Point, and T
T

Set Point, and T

OS

data is represented by a 9-bit, two’s complement word with
an LSB (Least Significant Bit) equal to 0.5

Temperature

a

125§C 0 1111 1010 0FAh

a

25§C 0 0011 0010 032h

a

0.5§C 0 0000 0001 001h

Set Point registers; and written to the

HYST

Set Point registers. Temperature

HYST

C:

§

Digital Output

Binary Hex

0§C 0 0000 0000 000h

b

0.5§C 1 1111 1111 1FFh

b

25§C 1 1100 1110 1CEh

b

55§C 1 10010010 192h

1.4 SHUTDOWN MODE

Shutdown mode is enabled by setting the shutdown bit in
the Configuration register via the I
reduces power supply current to 1 mA typical. O.S. is reset if
previously set. The I

2

C interface remains active. Activity on
the clock and data lines of the I
shutdown mode quiescent current. T
uration registers can be read from and written to in shut-

2

C bus. Shutdown mode

2

C bus may slightly increase

OS,THYST

, and Config-

down mode.

1.5 FAULT QUEUE

A fault queue of up to 6 faults is provided to prevent false
tripping of O.S. when the LM75 is used in noisy environ­ments. The number of faults set in the queue must occur
consecutively to set the O.S. output.

1.6 COMPARATOR/INTERRUPT MODE

As indicated in the O.S. Output Temperature Response Dia­gram,

Figure 4,

the events that trigger O.S. are identical for
either Comparator or Interrupt mode. The most important
difference is that in Interrupt mode the O.S. will remain set
indefinitely once it has been set. To reset O.S. while in Inter­rupt mode, perform a read from any register in the LM75.

OS

2.0 O. S. Output

2.1 DESCRIPTION

The O.S. output is an open-drain output and does not have
an internal pull-up. A ‘‘high’’ level will not be observed on
this pin until pull-up current is provided from some external
source, typically a pull-up resistor. Choice of resistor value
depends on many system factors but, in general, the pull-up
resistor should be as large as possible. This will minimize
any errors due to internal heating of the LM75. The maxi­mum resistance of the pull up, based on LM75 specification
for High Level Output Current, to provide a 2V high level, is
30 kX.

2.2 O.S. POLARITY

The O.S. output can be programmed via the configuration
register to be either active low (default mode), or active
high. In active low mode the O.S. output goes low when
triggered exactly as shown on the O.S. Output Temperature
Response Diagram,

Figure 4.

Active high simply inverts the

polarity of the O.S. output.

3.0 Application Hints

The LM75 can be applied easily in the same way as other
integrated-circuit temperature sensors. It can be glued or
cemented to a surface and its temperature will be within
about 0.2

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 of the LM75 die would be at an inter­mediate temperature between the surface temperature and
the air temperature.

The path of best thermal conductivity is between the die and
the GND pin, upon which the die is mounted. The printed­circuit board lands and traces connecting to the LM75 will
be the object whose temperature is being measured.

In probe type applications, the LM75 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 LM75 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 insure that moisture cannot corrode
the LM75 or its connections.

C of the surface temperature.

§

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4.0 Internal Register Structure

There are four data registers in the LM75, selected by the
Pointer register. At power-up the Pointer is set to ‘‘00’’; the
location for the Temperature Register. The Pointer register
latches whatever the last location it was set to. In Interrupt
Mode, a read from the LM75, or placing the device in shut­down mode, resets the O.S. output. All registers are read
and write, except the Temperature register which is read
only.

A write to the LM75 will always include the address byte and
the Pointer byte. A write to the Configuration register re­quires one data byte, and the T
quire two data bytes.

Reading the LM75 can take place either of two ways: If the
location latched in the Pointer is correct (most of the time it
is expected that the Pointer will point to the Temperature
register because it will be the data most frequently read
from the LM75), then the read can simply consist of an ad­dress byte, followed by retrieving the corresponding number
of data bytes. If the Pointer needs to be set, then an ad-

OS

and T

HYST

registers re-

TL/H/12658– 8

dress byte, pointer byte, repeat start, and another address
byte will accomplish a read.

The first data byte is the most significant byte with most
significant bit first, permitting only as much data as neces­sary to be read to determine temperature condition. For in­stance, if the first four bits of the temperature data indicates
an overtemperature condition, the host processor could im­mediately take action to remedy the excessive tempera­tures. At the end of a read, the LM75 can accept either
Acknowledge or No Acknowledge from the Master (No Ac­knowledge is typically used as a signal for the slave that the
Master has read its last byte).

An inadvertent 8-bit read from a 16-bit register, with the D7
bit low, can cause the LM75 to stop in a state where the
SDA line is held low. This can prevent any further bus com­munication until at least 9 additional clock cycles have oc­curred. Alternatively, the master can issue clock cycles until
SDA goes high, at which time issuing a ‘‘Stop’’ condition will
reset the LM75.

FIGURE 5. Inadvertent 8-Bit Read from 16-Bit Register where D7 is Zero (‘‘0’’)

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TL/H/12658– 9

4.0 Internal Register Structure (Continued)

4.1 POINTER REGISTER (Selects which registers will be read from or written to):

P7 P6 P5 P4 P3 P2 P1 P0

000000Register

P0-P1: Register Select:

P1 P0 Register

0 0 Temperature (Read only)(Power-up default)

0 1 Configuration (Read/Write)

10T

11TOS(Read/Write)

P2–P7: Must be kept zero.

4.2 TEMPERATURE REGISTER (Read Only):

D15 D14 D13 D12 D11 D10 D9 D8 D7 D6 D5 D4 D3 D2 D1 D0

MSB Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 LSB X X X X X X X

D0–D6: Undefined

D7–D15: Temperature Data. One LSBe0.5§C. Two’s complement format.

4.3 CONFIGURATION REGISTER (Read/Write):

D7 D6 D5 D4 D3 D2 D1 D0

0 0 0 Fault Queue O.S. Cmp/Int Shutdown

Power up default is with all bits ‘‘0’’ (zero).

D0: Shutdown: When set to 1 the LM75 goes to low power shutdown mode.

D1: Comparator/Interrupt mode: 0 is Comparator mode, 1 is Interrupt mode.

D2: O.S. Polarity: 0 is active low, 1 is active high. O.S. is an open-drain output under all conditions.

D3–D4: Fault Queue: Number of faults necessary to detect before setting O.S. output to avoid false tripping due to noise:

(Read/Write)

HYST

D4 D3 Number of Faults

0 0 1 (Power-up default)

012

104

116

Select

Polarity

D5–D7: These bits are used for production testing and must be kept zero for normal operation.

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4.0 Internal Register Structure (Continued)

4.4 T

D0–D6: Undefined

D7–D15: T
default is T

AND TOSREGISTER (Read/Write):

HYST

D15 D14 D13 D12 D11 D10 D9 D8 D7 D6 D5 D4 D3 D2 D1 D0

MSB Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 LSB X X X X X X X

Or TOSTrip Temperature Data. Power up

HYST
OS

e

80§C, T

HYST

e

75§C.

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I2C Timing Diagrams

TL/H/12658– 10

C Timing Diagram

2

FIGURE 6. I

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I2C Timing Diagrams (Continued)

TL/H/12658– 11

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C Timing Diagrams (Continued)

2

FIGURE 7. I

Typical Applications

When using I2C interface: program O.S. for active high and connect O.S. directly to Q2’s gate.

FIGURE 8. Simple Fan Controller I2C Interface Optional

FIGURE 9. Data Acquisition System with Temperature Input via I2C Bus

TL/H/12658– 12

TL/H/12658– 13

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Typical Applications (Continued)

FIGURE 10. Simple Thermostat I2C Interface Optional

TL/H/12658– 14

FIGURE 11. Temperature Sensor with Loudmouth Alarm (Barking Watchdog)

TL/H/12658– 15

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Physical Dimensions inches (millimeters)

8-Lead (0.150×Wide) Molded Small Outline Package, JEDEC

Order Number LM75CIM-3, LM75CIMX-3, LM75CIM-5 or LM75CIMX-5

NS Package Number M08A

C Digital Temperature Sensor and Thermal Watchdog

2

LM75 I

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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 OF NATIONAL
SEMICONDUCTOR CORPORATION. As used herein:

1. Life support devices or systems are devices or 2. A critical component is any component of a life
systems which, (a) are intended for surgical implant support device or system whose failure to perform can
into the body, or (b) support or sustain life, and whose be reasonably expected to cause the failure of the life
failure to perform, when properly used in accordance support device or system, or to affect its safety or
with instructions for use provided in the labeling, can effectiveness.
be reasonably expected to result in a significant injury
to the user.

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Corporation Europe Hong Kong Ltd. Japan Ltd.

1111 West Bardin Road Fax:
Arlington, TX 76017 Email: [e-mail] Ocean Centre, 5 Canton Rd. Fax: [phone]
Tel: [phone] Deutsch Tel:
Fax: [phone] English Tel:

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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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