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LM74
SPI/MICROWIRE
General Description
The LM74 is a temperature sensor, Delta-Sigma
analog-to-digital converter with an SPI and MICROWIRE
compatible interface. The host can query the LM74 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.
The LM74 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 LM74’s 3.0V 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 diskdrives,printers,electronic test equipment, and office electronics.
Applications
n System Thermal Management
n Personal Computers
n Disk Drives
n Office Electronics
™
Digital Temperature Sensor
December 1999
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 SO-8 package saves space
Key Specifications
n Supply Voltage 3.0V to 5.5V
n Supply Current operating 310 µA (typ)
520 µA (max)
shutdown 7 µA (typ)
n Temperature
Accuracy
−10˚C to 65˚C
−25˚C to 110˚C
−55˚C to 125˚C
±
1.25˚C(max)
±
2.1˚C(max)
±
3˚C(max)
LM74 SPI/MICROWIRE Digital Temperature Sensor
Simplified Block Diagram
DS100909-1
MICROWIRE®is a registeredtrademark of National Semiconductor Corporation.
© 1999 National Semiconductor Corporation DS100909 www.national.com
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Connection Diagram
LM74
Ordering Information
Order Number
LM74CIM-3 SO-8, M08A 3.0V to 3.6V 95 Units in Rail
LM74CIMX-3 SO-8, M08A 3.0V to 3.6V 2500 Units in Tape and Reel
LM74CIM-5 SO-8, M08A 4.5V to 5.5V 95 Units in Rail
LM74CIMX-5 SO-8, M08A 4.5V to 5.5V 2500 Units in Tape and Reel
Pin Descriptions
NS Package
Number
SO-8
DS100909-2
TOP VIEW
NS Package Number M08A
Supply Voltage Transport Media
Label Pin
SI/O 1 Slave Input/Output - Serial bus bi-directional data
SC 2 Slave Clock - Serial bus clock Shmitt trigger input
NC 3 No Connection No Connection
GND 4 Power Supply Ground Ground
NC 5 No Connection No Connection
NC 6 No Connection No Connection
CS
+
V
#
line. Shmitt trigger input.
line.
7 Chip Select input. From Controller
8 Positive Supply Voltage Input DC Voltage from 3.0V to 5.5V. Bypass with
Function Typical Connection
From and to Controller
From Controller
a 0.1 µF ceramic capacitor.
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Typical Application
LM74
DS100909-3
FIGURE 1. COP Microcontroller Interface
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Absolute Maximum Ratings (Note 1)
LM74
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
Soldering Information, Lead Temperature
SOP Package (Note 3)
Vapor Phase (60 seconds)
Infrared (15 seconds)
+
+ 0.3V
215˚C
220˚C
ESD Susceptibility (Note 4)
Human Body Model 2000V
Machine Model 200V
Operating Ratings
Specified Temperature Range T
(Note 5) −55˚C to +150˚C
Supply Voltage Range (+V
) +3.0V to +5.5V
S
MIN
to T
MAX
Temperature-to-Digital Converter Characteristics
Unless otherwise noted, these specifications apply for V
LM74CIM-5 (Note 6). Boldface limits apply for T
noted.
Parameter Conditions
=
Temperature Error (Note 6) T
−10˚C to +65˚C
A
=
T
−25˚C to +110˚C
A
=
T
−40˚C to +85˚C +2.65/−1.65
A
=
T
−40˚C to +110˚C +2.65/
A
=
−55˚C to +125˚C
T
A
=
T
−55˚C to +150˚C
A
+
=
3.0V to 3.6V for the LM74CIM-3 and V
=
=
to T
T
A
T
J
MIN
; all other limits T
MAX
Typical
(Note 7)
LM74-5
Limits
(Note 8)
±
1.25
±
2.1 +2.65/−2.15 ˚C (max)
+
=
=
A
4.5V to 5.5V for the
=
T
+25˚C, unless otherwise
J
LM74-3
Limits
(Note 8)
±
1.25 ˚C (max)
±
2.15 ˚C (max)
Units
(Limit)
+2.65/−2.15 ˚C (max)
−2.0
±
3.0
±
5.0
±
3.5 ˚C (max)
±
5.0 ˚C (max)
Resolution 13 Bits
Temperature Conversion Time (Note 9) 280 425 425 ms (max)
Quiescent Current Serial Bus Inactive 310 520 520 µA (max)
Serial Bus Active 310 µA
+
Shutdown Mode, V
Shutdown Mode, V
=
3.3V 7 µA
+
=
5V 8 µA
Logic Electrical Characteristics
DIGITAL DC CHARACTERISTICS
Unless otherwise noted, these specifications apply for V
LM74CIM-5. Boldface limits apply for T
=
T
A
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 V
Logical “0” Input Current V
All Digital Inputs 20 pF
High Level Output Voltage I
Low Level Output Voltage I
TRI-STATE Output Leakage
Current
+
=
=
J
3.0V to 3.6V for the LM74CIM-3 and V
to T
T
MIN
+
+
V
IN
IN
OH
OL
V
O
V
O
; all other limits T
MAX
=
3.0V to 3.6V 0.8 0.35 V (min)
=
4.5V to 5.5V 0.8 0.33 V (min)
+
=
V
=
0V −0.005 −3.0 µA (min)
=
−400 µA 2.4 V (min)
=
+2 mA 0.4 V (max)
=
GND
+
=
V
=
=
T
A
J
Typical
(Note 7)
0.005 3.0 µA (max)
+
=
+25˚C, unless otherwise noted.
4.5V to 5.5V for the
Limits
(Note 8)
+
V
+ 0.3 V (max)
+
V
x 0.3 V (max)
−1
+1
Units
(Limit)
µA (min)
µA(max)
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Logic Electrical Characteristics (Continued)
SERIAL BUS DIGITAL SWITCHING CHARACTERISTICS
Unless otherwise noted, these specifications apply for V
LM74CIM-5, C
to T
T
MIN
(load capacitance) on output lines=100 pF unless otherwise specified. Boldface limits apply for T
L
; all other limits T
MAX
=
=
T
+25˚C, unless otherwise noted.
A
J
Symbol Parameter Conditions
t
1
t
2
t
3
t
4
t
5
t
6
t
7
SC (Clock) Period 0.33
CS Low to SC (Clock) High Set-Up Time 100 ns (max)
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 (min)
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)
+
=
3.0V to 3.6V for the LM74CIM-3 and V
Typical
(Note 7)
+
=
4.5V to 5.5V for the
Limits
(Note 8)
DC
=
A
(Limit)
µs (min)
T
J
Units
(max)
LM74
=
FIGURE 2. Data Output Timing Diagram
FIGURE 3. TRI-STATE Data Output Timing Diagram
DS100909-4
DS100909-5
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Logic Electrical Characteristics (Continued)
LM74
DS100909-6
FIGURE 4. Data Input Timing Diagram
Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. DC andAC 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 “Surface Mounting Methods and Their Effect on Product Reliability” or the section titled “Surface Mount” found in a current National Semicon-
ductor 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. LM74 θ
tached to a printed circuit board with 2 oz. foil is summarized in the table below:
) at any pin exceeds the power supplies (V
I
Device Number
<
GND or V
I
NS Package
Number
>
+VS) the current at that pin should be limited to 5 mA. The 20 mA
I
(thermal resistance, junction-to-ambient) when at-
JA
Thermal
Resistance (θ
)
JA
LM74CIM M08A 160˚C/W
Note 6: Both part numbers of the LM74 will operate properly over the V+supply voltage range of 3V to 5.5V.The devices are tested and specified for rated tem-
perature error at their nominal supply voltage for temperature ranges of −10˚C to +65˚C, −55˚C to +125˚C and −55˚C to +150˚C. The temperature error for temperature ranges of −40˚C to +85˚C, −25˚C to +110˚C and −40˚C to +110˚C include error induced by power supply variation of
error will increase by
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 only to indicate how often temperature data is updated. The LM74 can be read at any time without regard to conversion state
(and will yield last conversion result). A conversion 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, minimize output loading. Higher sink currents can affect sensor accuracy with internal heating. This can cause an error of 0.64˚C at full
rated sink current and saturation voltage based on junction-to-ambient thermal resistance.
±
0.3˚C for a power supply voltage (V+) variation of±10%from the nominal value.
=
25˚C and represent most likely parametric norm.
A
±
5%from the nominal value. Temperature
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Electrical Characteristics
FIGURE 5. Temperature-to-Digital Transfer Function (Non-linear scale for clarity)
TRI-STATE Test Circuit
LM74
DS100909-8
DS100909-7
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Typical Performance Characteristics
LM74
Average Power-On Reset Voltage
vs Temperature
Static Supply Current vs
Temperature
Temperature Error
DS100909-23
1.0 Functional Description
The LM74 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 LM74 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 LM74 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.
1.2 SERIAL BUS INTERFACE
The LM74 operates as a slave and is compatible with SPI or
MICROWIRE bus specifications. Data is clocked out on the
falling edge of the 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
®
. Communica-
DS100909-21
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. A zero 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
•
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, before CS is taken HIGH, are detected by the LM74.
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.
DS100909-22
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1.0 Functional Description (Continued)
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
1.5 INTERNAL REGISTER STRUCTURE
The LM74 has three registers, the temperature register, the
configuration register and the manufacturer’s/device identifi-
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 Bit11Bit10Bit 9 Bit 8 Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 LSB 1 X X
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 0000 0000 0XX. This is the
manufacturer’s/Device ID information. The first 5-bits of the
field (1000 0XXX) are reserved for manufacturer’s ID.
cation register. The temperature and manufacturer’s/device
identification registers are read only.The configuration register is write only.
Figure 7
c. The serial bus is still active when the
LM74
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
LM74
a) Reading Continuous Conversion - Single Eight-Bit Frame
b) Reading Continuous Conversion - Two Eight-Bit Frames
3.0 Application Hints
To get the expected results when measuring temperature
with an integrated circuit temperature sensor like the LM74,
it is important to understand that the sensor measures its
own die temperature. For the LM74, the best thermal path
between the die and the outside world is through the LM74’s
pins. In the SO-8 package all the pins on the LM74 will have
an equal effect on the die temperature. Because the pins
represent a good thermal path to the LM74 die, the LM74 will
provide an accurate measurement of the temperature of the
printed circuit board on which it is mounted. There is a less
efficient thermal path between the plastic package and the
LM74 die. If the ambient air temperature is significantly different from the printed circuit board temperature, it will have
a small effect on the measured temperature.
DS100909-14
DS100909-15
DS100909-18
c) Writing Shutdown Control
FIGURE 7. Timing Diagrams
In probe-type applications, the LM74 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
LM74 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 LM74 or
its connections.
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4.0 Typical Applications
FIGURE 8. Temperature monitor using Intel 196 processor
LM74
DS100909-20
DS100909-19
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
Order Number LM74CIM-3, LM74CIMX-3, LM74CIM-5 or LM74CIMX-5
8-Lead Molded Small Outline Package
NS Package Number M08A
LM74 SPI/MICROWIRE Digital Temperature Sensor
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.
National Semiconductor
Corporation
Americas
Tel: 1-800-272-9959
Fax: 1-800-737-7018
Email: support@nsc.com
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Fax: +49 (0) 1 80-530 85 86
Email: europe.support@nsc.com
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English Tel: +49 (0) 1 80-532 78 32
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Italiano Tel: +49 (0) 1 80-534 16 80
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
Asia Pacific Customer
Response Group
Tel: 65-2544466
Fax: 65-2504466
Email: sea.support@nsc.com
National Semiconductor
Japan Ltd.
Tel: 81-3-5639-7560
Fax: 81-3-5639-7507
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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