LM71
SPI/MICROWIRE
TM
13-Bit Plus Sign Temperature Sensor
General Description
The LM71 is a low-power, high-resolution digital temperature
sensor with an SPI and MICROWIRE compatible interface,
available in the 5-pin SOT23 or the 6-pin LLP (no pull back)
package. The host can query the LM71 at any time to read
temperature. Its low operating current is useful in systems
where low power consumption is critical.
The LM71 has 13-bit plus sign temperature resolution
(0.03125C per LSB) while operating over a temperature
range of -40C to +150C.
The LM71's 2.65V to 5.5V supply voltage range, fast con-
version rate, low supply current, and simple SPI interface
make it ideal for a wide range of applications.
Applications
n
System Thermal Management
n
Personal Computers
n
Portable Electronic Devices
n
Disk Drives
n
Office Electronics
n
Electronic Test Equipment
n
Vending Machines
Features
n
SOT23-5 or No-Pull-Back LLP-6 Packages
n
Operates over a full -40C to +150C range
n
SPI and MICROWIRE Bus interface
Key Specifications
j
Supply Voltage
2.65V to 5.5V
j
Supply Current
operating
300 A (typ)
550 A (max)
j
Temperature
Accuracy
-10C to +65C
1.5C (max)
-40C to 150C
+3/- 2C (max)
j
Temperature
Resolution
31.25 mC
Simplified Block Diagram
20031701
MICROWIRE
TM
is a trademark of National Semiconductor Corporation.
TRI-STATE
is a registered trademark of National Semiconductor Corporation.
March 2004
LM71
SPI/MICROWIRE
13-Bit
Plus
Sign
T
emperature
Sensor
2004 National Semiconductor Corporation
DS200317
www.national.com
Connection Diagrams
SOT23-5
LLP-6 No Pull-Back
20031702
TOP VIEW
NS Package Number MF05A
20031728
TOP VIEW
NS Package Number SDE06A
Ordering Information
Order Number
Package
Marking
NS Package
Number
Supply Voltage
Transport Media
LM71CIMF
T16C
MF05A
2.65V to 5.5V
3000 Units in Tape and Reel
LM71CISD
LM71C
SDE06A
2.65V to 5.5V
4500 Units in Tape and Reel
LM71
www.national.com
2
Pin Descriptions
Label
Pin Number
Function
Typical Connection
SOT23-5
LLP-6
CS
1
4
Chip Select input
From controller
GND
2
2, 5
Power Supply Ground
Connect all GND Pins to ground
SI/O
3
3
Slave Input/Output - Serial bus
bi-directional data line. Shmitt trigger input.
From and to controller
SC
4
1
Slave Clock - Serial bus clock Shmitt
trigger input line
From controller
V
+
5
6
Positive Supply Voltage Input
DC voltage from 2.65V to 5.5V. Bypass with a
0.1 F ceramic capacitor.
Typical Application
20031703
FIGURE 1. COP Microcontroller Interface
LM71
www.national.com
3
Absolute Maximum Ratings
(Note 1)
Supply Voltage
-0.3V to 6.0V
Voltage at any Pin
-0.3V to V
+
+ 0.3V
Input Current at any Pin (Note 2)
5 mA
Storage Temperature
-65C to +150C
Soldering Information, Lead Temperature
SOT23-5 Package (Note 3)
Vapor Phase (60 seconds)
Infrared (15 seconds)
215C
220C
LLP-6 Package (Note 3)
Infrared (5 seconds)
215C
ESD Susceptibility (Note 4)
Human Body Model
Machine Model
2000V
200V
Operating Ratings
Specified Temperature Range
(Note 5)
T
MIN
to T
MAX
LM71CIMF, LM71CISD
-40C to +150C
Supply Voltage Range (+V
S
)
LM71CIMF, LM71CISD
+2.65V to +5.5V
Temperature-to-Digital Converter Characteristics
Unless otherwise noted, these specifica-
tions apply for V
+
= 2.65V to 3.6V (Note 6). Boldface limits apply for T
A
= T
J
= T
MIN
to T
MAX
; all other limits T
A
= T
J
=
+25C, unless otherwise noted.
Parameter
Conditions
Typical
(Note 7)
LM71CIMF
LM71CISD
Limits
(Note 8)
Units
(Limit)
Temperature Error
(Note 6)
T
A
= -10C to +65C
1.5
C (max)
T
A
= -40C to +85C
2.0
C (max)
T
A
= -40C to +150C
+3/-2
C (max)
Resolution
14
0.03125
Bits
C
Temperature
Conversion Time
(Note 9)
200
270
ms (max)
Quiescent Current
Serial Bus Inactive
300
550
A (max)
Logic Electrical Characteristics
DIGITAL DC CHARACTERISTICS Unless otherwise noted, these specifications apply for V
+
= 2.65V to 3.6V (Note 6). Bold-
face limits apply for T
A
= T
J
= T
MIN
to T
MAX
; all other limits T
A
= T
J
= +25C, unless otherwise noted.
Symbol
Parameter
Conditions
Typical
(Note 7)
Limits
(Note 8)
Units
(Limit)
V
IN(1)
Logical "1" Input Voltage
V
+
x 0.7
V (min)
V
+
+ 0.3
V (max)
V
IN(0)
Logical "0" Input Voltage
-0.3
V (min)
V
+
x 0.3
V (max)
Input Hysteresis Voltage
V
+
= 3.0V to 3.6V
0.4
0.33
V (min)
I
IN(1)
Logical "1" Input Current
V
IN
= V
+
0.005
3.0
A (max)
I
IN(0)
Logical "0" Input Current
V
IN
= 0V
-0.005
-3.0
A (min)
C
IN
All Digital Inputs
20
pF
V
OH
High Level Output Voltage
I
OH
= -400 A
2.4
V (min)
V
OL
Low Level Output Voltage
I
OL
= +2 mA
0.4
V (max)
I
O_TRI-STATE
TRI-STATE
Output Leakage
Current
V
O
= GND
V
O
= V
+
-1
+1
A (min)
A (max)
LM71
www.national.com
4
Logic Electrical Characteristics
(Continued)
SERIAL BUS DIGITAL SWITCHING CHARACTERISTICS Unless otherwise noted, these specifications apply for V
+
= 2.65V
to 3.6V (Note 6); C
L
(load capacitance) on output lines = 100 pF unless otherwise specified. Boldface limits apply for T
A
= T
J
= T
MIN
to T
MAX
; all other limits T
A
= T
J
= +25C, unless otherwise noted.
Symbol
Parameter
Conditions
Typical
(Note 7)
Limits
(Note 8)
Units
(Limit)
t
1
SC (Clock) Period
0.16
DC
s (min)
(max)
t
2
CS Low to SC (Clock) High Set-Up Time
100
ns (min)
t
3
CS Low to Data Out (SO) Delay
70
ns (max)
t
4
SC (Clock) Low to Data Out (SO) Delay
70
ns (max)
t
5
CS High to Data Out (SO) TRI-STATE
200
ns (max)
t
6
SC (Clock) High to Data In (SI) Hold Time
50
ns (min)
t
7
Data In (SI) Set-Up Time to SC (Clock) High
30
ns (min)
20031704
FIGURE 2. Data Output Timing Diagram
20031705
FIGURE 3. TRI-STATE Data Output Timing Diagram
LM71
www.national.com
5
Logic Electrical Characteristics
(Continued)
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
I
) at any pin exceeds the power supplies (V
I
<
GND or V
I
>
+V
S
) the current at that pin should be limited to 5 mA.
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 k
resistor. Machine model, 200 pF discharged directly into each pin.
Note 5: The life expectancy of the LM71 will be reduced when operating at elevated temperatures. LM71
JA
(thermal resistance, junction-to-ambient) when
attached to a printed circuit board with 2 oz. foil is summarized in the table below:
Device Number
NS Package
Number
Thermal
Resistance (
JA
)
LM71CIMF
MF05A
250C/W
LM71CISD
SDE06A
57.6C/W
Note 6: The LM71 will operate properly over the V
+
supply voltage range of 2.65V to 5.5V.
Note 7: Typicals are at T
A
= 25C and represent most likely parametric norm.
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 LM71 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 0.64C at full
rated sink current and saturation voltage based on junction-to-ambient thermal resistance.
20031706
FIGURE 4. Data Input Timing Diagram
LM71
www.national.com
6
Electrical Characteristics
TRI-STATE Test Circuit
20031708
FIGURE 5. Temperature-to-Digital Transfer Function (Non-linear scale for clarity)
20031707
FIGURE 6.
LM71
www.national.com
7
Typical Performance Characteristics
Static Supply Current vs. Temperature
Temperature Error
20031796
20031797
1.0 Functional Description
The LM71 temperature sensor incorporates a temperature
sensor and 13-bit plus sign
ADC (Delta-Sigma Analog-to-
Digital Converter). Compatibility of the LM71's three wire
serial interface with SPI and MICROWIRE allows simple
communications with common microcontrollers and proces-
sors. Shutdown mode can be used to optimize current drain
for different applications. A Manufacture's/Device ID register
identifies the LM71 as National Semiconductor product.
1.1 POWER UP AND POWER DOWN
The LM71 always powers up in a known state. The power up
default condition is continuous conversion mode. Immedi-
ately after power up the LM71 will output an erroneous code
until the first temperature conversion has completed.
When the supply voltage is less than about 1.6V (typical),
the LM71 is considered powered down. As the supply volt-
age 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 LM71 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 com-
munication 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. Communication
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. CS can be taken high at any
time during the transmit phase. If CS is brought low in the
middle of a conversion the LM71 will complete the conver-
sion 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 LM71 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. All zeros
must be shifted in order to place the LM71 into continuous
conversion mode. Only the following codes should be trans-
mitted to the LM71:
00 hex for continuous conversion
FF hex for shutdown
Another code may place the part into a test mode. Test
modes are used by National Semiconductor to thoroughly
test the function of the LM71 during production testing. Only
eight bits have been defined above since only the last eight
transmitted are detected by the LM71, 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 300 ms will have to pass for a conversion to
complete before the LM71 actually transmits temperature
data.
LM71
www.national.com
8
1.0 Functional Description
(Continued)
1.3 TEMPERATURE DATA FORMAT
Temperature data is represented by a 14-bit, two's comple-
ment word with an LSB (Least Significant Bit) equal to
0.03125C:
Temperature
Digital Output
Binary
Hex
+150C
0100 1011 0000 0011
4B03
+125C
0011 1110 1000 0011
3E83
+25C
0000 1100 1000 0011
0C83
+0.03125C
0000 0000 0000 0111
0007
0C
0000 0000 0000 0011
0003
-0.03125C
1111 1111 1111 1111
FFFF
-25C
1111 0011 1000 0011
F383
-40C
1110 1100 0000 0011
EC03
The first data byte is the most significant byte with most
significant bit first, permitting only as much data as neces-
sary 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 im-
mediately take action to remedy the excessive tempera-
tures.
1.4 SHUTDOWN MODE/MANUFACTURER'S ID
Shutdown mode is enabled by writing XX FF to the LM71 as
shown in Figure 7c. The serial bus is still active when the
LM71 is in shutdown. When in shutdown mode the LM71
always will output 1000 0000 0000 1111. This is the
manufacturer's/Device ID information. The first 5-bits of the
field (1000 0XXX) are reserved for manufacturer's ID.
1.5 INTERNAL REGISTER STRUCTURE
The LM71 has three registers, the temperature register, the
configuration register and the manufacturer's/device identifi-
cation register. The temperature and manufacturer's/device
identification registers are read only. The configuration reg-
ister 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
X
X
X
X
X
X
X
X
Shutdown
D0D15 set to XX FF hex enables shutdown mode.
D0D15 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 LM71 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 12
Bit 11
Bit 10
Bit 9
Bit 8
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit1
LSB
1
1
D0D1: Logic 1 will be output on SI/0.
D2D15: Temperature Data. One LSB = 0.03125C. Two's complement format.
1.5.3 Manufacturer/Device ID Register
(Read Only):
D15
D14
D13
D12
D11
D10
D9
D8
D7
D6
D5
D4
D3
D2
D1
D0
1
0
0
0
0
0
0
0
0
0
0
0
1
1
1
1
D0D1: Logic 1 will be output on SI/0.
D2D15: Manufacturer's/Device ID Data. This register is accessed whenever the LM71 is in shutdown mode.
LM71
www.national.com
9
2.0 Serial Bus Timing Diagrams
3.0 Application Hints
To get the expected results when measuring temperature
with an integrated circuit temperature sensor like the LM71,
it is important to understand that the sensor measures its
own die temperature. For the LM71, the best thermal path
between the die and the outside world is through the LM71's
pins. In the SOT23 package, all the pins on the LM71 will
have an equal effect on the die temperature. Because the
pins represent a good thermal path to the LM71 die, the
LM71 will provide an accurate measurement of the tempera-
ture of the printed circuit board on which it is mounted. There
is a less efficient thermal path between the plastic package
and the LM71 die. If the ambient air temperature is signifi-
cantly different from the printed circuit board temperature, it
will have a small effect on the measured temperature.
In probe-type applications, the LM71 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
LM71 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 LM71
or its connections.
20031714
a) Reading Continuous Conversion - Single Eight-Bit Frame
20031715
b) Reading Continuous Conversion - Two Eight-Bit Frames
20031718
c) Writing Shutdown Control
FIGURE 7. Timing Diagrams
LM71
www.national.com
10
4.0 Typical Applications
20031720
FIGURE 8. Temperature monitor using Intel 196 processor
20031719
FIGURE 9. LM71 digital input control using micro-controller's general purpose I/O.
LM71
www.national.com
11
Physical Dimensions
inches (millimeters) unless otherwise noted
Order Number LM71Top View
CIMF
NS Package Number MF05A
LM71
www.national.com
12
Physical Dimensions
inches (millimeters) unless otherwise noted (Continued)
Order Number LM71Bottom View
CISD
NS Package Number SDE06A
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 certifies that the products and packing materials 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.
National Semiconductor
Americas Customer
Support Center
Email: new.feedback@nsc.com
Tel: 1-800-272-9959
National Semiconductor
Europe Customer Support Center
Fax: +49 (0) 180-530 85 86
Email: europe.support@nsc.com
Deutsch Tel: +49 (0) 69 9508 6208
English
Tel: +44 (0) 870 24 0 2171
Franais Tel: +33 (0) 1 41 91 8790
National Semiconductor
Asia Pacific Customer
Support Center
Email: ap.support@nsc.com
National Semiconductor
Japan Customer Support Center
Fax: 81-3-5639-7507
Email: jpn.feedback@nsc.com
Tel: 81-3-5639-7560
www.national.com
LM71
SPI/MICROWIRE
13-Bit
Plus
Sign
T
emperature
Sensor
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.
PDF 
ZIP