National Semiconductor LM74A Technical data

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LM74A

LM74A SPI/MICROWIRE 12-Bit Plus Sign Temperature Sensor (LM74 in Die Form)

December 2001

SPI/MICROWIRE

™

12-Bit Plus Sign Temperature Sensor

(LM74 in Die Form)

General Description

The LM74A is a temperature sensor, Delta-Sigma
analog-to-digital converter with an SPI and MICROWIRE
compatible interface in die form. The host can query the
LM74A at any time to read temperature. A shutdown mode
decreases power consumption to less than 10 µA. This
mode is useful in systems where low average power con­sumption is critical.

This particular data sheet applies to the LM74 in die form.
The LM74 is available in the SO-8 package as well as an
5-Bump micro SMD package please refer to LM74 data
sheet for detailed specifictions pertaining to the packaged
parts.

The LM74A has 12-bit plus sign temperature resolution
(0.0625˚C per LSB) while operating over a temperature
range of−55˚C to +150˚C. The LM74Aaccuracy of
specified over a temperature range of 0˚C to +150˚C.

The LM74A’s 4.5V to 5.5V supply voltage range, low supply
current and simple SPI interface make it ideal for a wide
range of applications. These include thermal management
and protection applications in hard disk drives, printers, elec­tronic test equipment, and office electronics.

Applications

n System Thermal Management
n Personal Computers

±

3.5˚C is

n Disk Drives
n Office Electronics
n Electronic Test Equipment

Features

n 0.0625˚C temperature resolution.
n Shutdown mode conserves power between temperature

reading

n SPI and MICROWIRE Bus interface
n LM74 is available in a 5-Bump micro SMD and 8-pin

SOP

Key Specifications

j

Supply Voltage 4.5V to 5.5V

j

Supply Current operating 310µA (typ)

520µA (max)

shutdown 8µA (typ)

j

Temperature

Accuracy

0˚C to 140˚C

140˚C to 150˚C

±

3.0˚C(max)

±

3.5˚C(max)

Simplified Block Diagram

20017701

MICROWIRE®is a registered trademark of National Semiconductor Corporation.

© 2001 National Semiconductor Corporation DS200177 www.national.com

Connection Diagram

LM74A

LM74A

Bond Pad Layout

1.40mm x 1.57 mm (55 x 62 mils)

Bond Pad Mechanical Dimensions

Dimensions of bond pad coordinates are in millimeters.
Origin of coordinates: center of die.
X-Direction is in the longitudinal axis of the die.
Coordinates refer to center of Bond Pad.

#

Pin
1 -0.569 mm +0.585 mm
2 -0.537 mm +0.314 mm
3 -0.569 mm -0.554 mm
4 n/a n/a
5 +0.537 mm +0.277 mm
6 +0.569 mm +0.569 mm
Back

XY

Ordering Information

Order Number

LM74A MDA No Package, Die 4.5V to 5.5V 7k unit surftape tape-and-reel

NS Package

Number

TOP VIEW

20017727

Supply Voltage Transport Media

Pin Descriptions

Label Pin

SI/O 1 Slave Input/Output - Serial bus bi-directional data line.

SC 2 Slave Clock - Serial bus clock Shmitt trigger input

GND 3 Power Supply Ground Ground
NC 4 No Connection No Connection
CS

+

V

Back (Backside) Can go to GND connection

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#

Shmitt trigger input.

line.

5 Chip Select input. From Controller
6 Positive Supply Voltage Input DC Voltage from 4.5V to 5.5V. Bypass with a

Function Typical Connection

From and to Controller

From Controller

0.1 µF ceramic capacitor.

Typical Application

LM74A

20017703

FIGURE 1. COP Microcontroller Interface

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Absolute Maximum Ratings (Note 1)

LM74A

Supply Voltage −0.3V to 6.0V
Voltage at any Pin −0.3V to V
Input Current at any Pin (Note 2) 5 mA
Package Input Current (Note 2) 20 mA
Storage Temperature −65˚C to +150˚C

+

+ 0.3V

Operating Ratings

Operating Temperature Range 0˚C to +150˚C
Specified Temperature Range T

(Note 5)

LM74A 0˚C to +150˚C
Supply Voltage Range (+V

) +4.5V to +5.5V

S

ESD Susceptibility (Note 4)

Human Body Mode
Machine Model

2000V

200V

Temperature-to-Digital Converter Characteristics

Unless otherwise noted, these specifications apply for V+= 4.5V to 5.5V (Note 6). Boldface limits apply for TA=TJ=T
to T

Temperature Error (Note 6) T

Resolution 13 Bits
Temperature Conversion Time (Note 9) 280 425 ms (max)
Quiescent Current Serial Bus

; all other limits TA=TJ=+25˚C, unless otherwise noted.

MAX

Parameter Conditions

= 0˚C to

A

+140˚C
T

= +140˚C

A

to +150˚C

Inactive
Serial Bus

Active
Shutdown

Mode, V

+

=

5V

Typical

(Note 7)

Limits

(Note 8)

±

3.0

±

3.5 ˚C (max)

310 520 µA (max)

310 µA

8µA

to T

MIN

Units

(Limit)

˚C (max)

MAX

MIN

Logic Electrical Characteristics

DIGITAL DC CHARACTERISTICS

Unless otherwise noted, these specifications apply for V

to T

; all other limits TA=TJ=+25˚C, unless otherwise noted.

MAX

Symbol Parameter Conditions

V

IN(1)

V

IN(0)

Logical “1” Input Voltage V+x 0.7 V (min)

Logical “0” Input Voltage −0.3 V (min)

Input Hysteresis Voltage V

I

IN(1)

I

IN(0)

C

IN

V

OH

V

OL

I

O_TRI-STATE

Logical “1” Input Current VIN=V
Logical “0” Input Current VIN= 0V −0.005 −3.0 µA (min)
All Digital Inputs 20 pF
High Level Output Voltage IOH= −400 µA 2.4 V (min)
Low Level Output Voltage IOL=+2mA 0.4 V (max)
TRI-STATE Output Leakage

Current

+

= 4.5V to 5.5V (Note 6). Boldface limits apply for TA=TJ=T

+

= 4.5V to 5.5V 0.8 0.33 V (min)

+

VO= GND

+

=V

V

O

Typical

(Note 7)

Limits

(Note 8)

+

V

+ 0.3 V (max)

+

V

x 0.3 V (max)

Units

(Limit)

0.005 3.0 µA (max)

−1
+1

µA (min)

µA

(max)

MIN

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SERIAL BUS DIGITAL SWITCHING CHARACTERISTICS

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

+

= 4.5V to 5.5V (Note 6); CL(load capacitance) on output lines = 100

A=TJ=TMIN

to T

MAX

otherwise noted.

Symbol Parameter Conditions

t

1

t

2

t

3

t

4

t

5

t

6

t

7

SC (Clock) Period 0.16

CS Low to SC (Clock) High Set-Up Time 100 ns (min)
CS Low to Data Out (SO) Delay 70 ns (max)
SC (Clock) Low to Data Out (SO) Delay 100 ns (max)
CS High to Data Out (SO) TRI-STATE 200 ns (max)
SC (Clock) High to Data In (SI) Hold Time 50 ns (min)
Data In (SI) Set-Up Time to SC (Clock) High 30 ns (min)

; all other limits TA=TJ= +25˚C, unless

Typical

(Note 7)

Limits

(Note 8)

Units

(Limit)

µs (min)

DC

(max)

LM74A

FIGURE 2. Data Output Timing Diagram

FIGURE 3. TRI-STATE Data Output Timing Diagram

20017704

20017705

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LM74A

20017706

FIGURE 4. Data Input Timing Diagram

Note 1: Absolute Maximum Ratingsindicate limits beyond which damage tothe device may occur. DC and AC electrical specifications donot 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 “Surface Mounting Methods and Their Effect on Product Reliability” or the section titled “Surface Mount” found in a current National

Semiconductor Linear Data Book for other methods of soldering surface mount devices.

Note 4: Human body model, 100 pF discharged through a 1.5 kΩ resistor. Machine model, 200 pF discharged directly into each pin.
Note 5: The life expectancy of the LM74 will be reduced when operating at elevated temperatures.
Note 6: All LM74 parts will function over the V

+140˚C, and 0˚C to +150˚C include error induced by power supply variation of

Note 7: Typicals are at T
Note 8: Limits are guaranteed to National’s AOQL (Average Outgoing Quality Level).
Note 9: This specification is provided onlyto indicate how often temperature data is updated. The LM74A can be read at any timewithout regard to conversion state

(and will yield last conversion result). Aconversion in progress will not be interrupted. The output shift register will be updated at the completion of the read and a
new conversion restarted.

Note 10: For best accuracy, minimizeoutput loading. Higher sink currents can affect sensor accuracy with internal heating. This can cause an errorof 0.64˚C at full
rated sink current and saturation voltage based on junction-to-ambient thermal resistance.

) at any pin exceeds the power supplies (V

I

+

supply voltage range of 3V to 5.5V. The LM74A temperature error specifications for temperature ranges of 0˚C to

= 25˚C and represent most likely parametric norm.

A

<

GND or V

I

±

10% from the nominal value of 5V.

>

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

I

Electrical Characteristics

FIGURE 5. Temperature-to-Digital Transfer Function (Non-linear scale for clarity)

20017708

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TRI-STATE Test Circuit

20017707

FIGURE 6.

Typical Performance Characteristics

Average Power-On Reset Voltage vs Temperature Static Supply Current vs Temperature

LM74A

Temperature Error

20017723

20017726

20017721

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1.0 Functional Description

LM74A

The LM74A temperature sensor incorporates a band-gap
type temperature sensor and 12-bit plus sign ∆Σ ADC
(Delta-Sigma Analog-to-Digital Converter). Compatibility of
the LM74’s three wire serial interface with SPI and MI­CROWIRE allows simple communications with common mi­crocontrollers and processors. Shutdown mode can be used
to optimize current drain for different applications. A
Manufacture’s/Device ID register identifies the LM74 as Na­tional Semiconductor product.

1.1 POWER UP AND POWER DOWN

The LM74A always powers up in a known state. The power
up default condition is continuous conversion mode. Imme­diatly after power up the LM74 will output an erroneous code
until the first temperature conversion has completed.

When the supply voltage is less than about 1.6V (typical),
the LM74A is considered powered down. As the supply
voltage rises above the nominal 1.6V power up threshold,
the internal registers are reset to the power up default state
described above.

3F hex

•

7F hex

•

FF hex

•

any others may place the part into a Test Mode. Test Modes
are used by National Semiconductor to thoroughly test the
function of the LM74 during production testing. Only eight
bits have been defined above since only the last eight trans­mitted are detected by the LM74, before CS is taken HIGH.

The following communication can be used to determine the
Manufacturer’s/Device ID and then immediately place the
part into continuous conversion mode. With CS continuously
low:

Read 16 bits of temperature data

•

Write 16 bits of data commanding shutdown

•

Read 16 bits of Manufacture’s/Device ID data

•

Write 8 to 16 bits of data commanding Conversion Mode

•

Take CS HIGH.

•

Note that 250 ms will have to pass for a conversion to
complete before the LM74 actually transmits temperature
data.

1.2 SERIAL BUS INTERFACE

The LM74A operates as a slave and is compatible with SPI
or MICROWIRE bus specifications. Data is clocked out on
the falling edge ofthe serial clock (SC), while data is clocked
in on the rising edge of SC. A complete transmit/receive
communication will consist of 32 serial clocks. The first 16
clocks comprise the transmit phase of communication, while
the second 16 clocks are the receive phase.

When CS is high SI/O will be in TRI-STATE
tion should be initiated by taking chip select (CS) low. This
should not be done when SC is changing from a low to high
state. Once CS is low the serial I/O pin (SI/O) will transmit
the first bit of data. The master can then read this bit with the
rising edge of SC. The remainder of the data will be clocked
out by the falling edge of SC. Once the 14 bits of data (one
sign bit, twelve temperature bits and 1 high bit) are transmit­ted the SI/O line will go into TRI-STATE. CS can be taken
high at any time during the transmit phase. If CS is brought
low in the middle of a conversion the LM74 will complete the
conversion and the output shift register will be updated after
CS is brought back high.

The receive phase of a communication starts after 16 SC
periods. CS can remain low for 32 SC cycles. The LM74 will
read the data available on the SI/O line on the rising edge of
the serial clock. Input data is to an 8-bit shift register. The
part will detect the last eight bits shifted into the register.The
receive phase can last up to 16 SC periods.All ones must be
shifted in order to place the part into shutdown.Azero in any
location will take the LM74 out of shutdown. The following
codes should only be transmitted to the LM74:

00 hex

•

01 hex

•

03 hex

•

07 hex

•

0F hex

•

1F hex

•

®

. Communica-

1.3 TEMPERATURE DATA FORMAT

Temperature data is represented by a 13-bit, two’s comple­ment word with an LSB (Least Significant Bit) equal to

0.0625˚C:

Temperature Digital Output

Binary Hex

+150˚C 0100 1011 0000 0111 4B 07h
+125˚C 0011 1110 1000 0111 3E 87h

+25˚C 0000 1100 1000 0111 0B 87h

+0.0625˚C 0000 0000 0000 1111 00 0Fh

0˚C 0000 0000 0000 0111 00 07h

−0.0625˚C 1111 1111 1111 1111 FF FFh

−25˚C 1111 0011 1000 0111 F3 87h

−55˚C 1110 0100 1000 0111 E4 87h

Note: The last two bits are TRI-STATE and depicted as one
in the table.

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 indicate
an overtemperature condition, the host processor could im­mediately take action to remedy the excessive tempera­tures.

1.4 SHUTDOWN MODE/MANUFACTURER’S ID

Shutdown mode is enabled by writing XX FF to the LM74 as
shown in
LM74 is in shutdown. Current draw drops to less than 10 µA
between serial communications. When in shutdown mode
the LM74 always will output 1000 00000000 0XX. This is the
manufacturer’s/Device ID information. The first 5-bits of the
field (1000 0XXX) are reserved for manufacturer’s ID.

Figure 7

c. The serial bus is still active when the

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1.0 Functional Description (Continued)

1.5 INTERNAL REGISTER STRUCTURE

The LM74 has three registers, the temperature register, the
configuration register and the manufacturer’s/device identifi­cation register. The temperature and manufacturer’s/device
identification registers are read only. The configuration reg­ister is write only.

1.5.1 CONFIGURATION REGISTER

(Selects shutdown or continuous conversion modes):

(Write Only):

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

XXXXXXXX Shutdown

D0–D15 set to XX FF hex enables shutdown mode.
D0–D15 set to 00 00 hex sets Continuous conversion mode.
Note: setting D0-D15 to any other values may place the LM70 into a manufacturer’s test mode, upon which the LM74 will stop

responding as described. These test modes are to be used for National Semiconductor production testing only. See Section 1.2
Serial Bus Interface for a complete discussion.

1.5.2 TEMPERATURE REGISTER

(Read Only):

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

MSB Bit 11 Bit 10 Bit 9 Bit 8 Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 LSB 1 X X

LM74A

D0–D1: Undefined. TRI-STATE will be output on SI/0.
D2: Always set high.
D3–D15: Temperature Data. One LSB = 0.0625˚C. Two’s complement format.

1.5.3 MANUFACTURER’S/DEVICE ID REGISTER

(Read Only):

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

10000000000000XX

D0–D1: Undefined. TRI-STATE will be output on SI/0.
D2–D15: Manufacturer’s/Device ID Data. This register is accessed whenever the LM74 is in shutdown mode.

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2.0 Serial Bus Timing Diagrams

LM74A

a) Reading Continuous Conversion - Single Eight-Bit Frame

20017714

b) Reading Continuous Conversion - Two Eight-Bit Frames

c) Writing Shutdown Control

FIGURE 7. Timing Diagrams

20017715

20017718

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3.0 Application Hints

3.1 LIGHT SENSITIVITY

The LM74 in die form should not be exposed to ultraviolet
light. Exposing the LM74A to bright sunlight will not immedi­atly cause a change in the output reading. Our experiments
show that directly exposing the circuit side (pad side) of the

4.0 Typical Applications

die to high intensity (≥1mW/cm
a wavelength of 254nm, for greater than 20 minutes will
deprogram the EEPROM cells in the LM74. Since the EE­PROM is used for storing calibration coefficients, the LM74
will function but the temperature accuracy will no longer be
as specified. Light can penetrate through the side of the die
as well.

2

) ultraviolet light, centered at

LM74A

20017720

FIGURE 8. Temperature monitor using Intel 196 processor

20017719

FIGURE 9. LM74 digital input control using micro-controller’s general purpose I/O.

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Physical Dimensions inches (millimeters)

unless otherwise noted

Bond Pad Layout

20017727

Order Number LM74A MDA

Bare Die

TOP VIEW

1.40mm x 1.57 mm (55 x 62 mils)

For Bond Pad Mechanical Dimensions see Connection Diagram Section

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

LM74A SPI/MICROWIRE 12-Bit Plus Sign Temperature Sensor (LM74 in Die Form)

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]

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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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