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LM75A
SNOS808P – JANUARY 2000 – REVISED DECEMBER 2014
LM75A Digital Temperature Sensor and Thermal Watchdog With Two-Wire Interface
1 Features
3 Description
•
•
•
The LM75A is an industry-standard digital
temperature sensor with an integrated sigma-delta
analog-to-digital converter (ADC) and I2C interface.
The LM75A provides 9-bit digital temperature
readings with an accuracy of ±2°C from –25°C to
100°C and ±3°C over –55°C to 125°C.
1
•
•
No External Components Required
Shutdown Mode to Minimize Power Consumption
Up to Eight LM75As can be Connected to a Single
Bus
Power up Defaults Permit Stand-Alone Operation
as Thermostat
Key Specifications:
– Supply Voltage
– LM75A: 2.7 V to 5.5 V
– Supply Current
– Operating: 280 μA (Typical)
– Shutdown: 4 μA (Typical)
– Temperature Accuracy
– 25°C to 100°C: ±2°C (Max)
– 55°C to 125°C: ±3°C (Max)
The LM75A operates with a single supply from 2.7 V
to 5.5 V. Communication is accomplished over a
2-wire interface which operates up to 400 kHz. The
LM75A has three address pins, allowing up to eight
LM75A devices to operate on the same 2-wire bus.
The LM75A has a dedicated overtemperature output
(O.S.) with programmable limit and hysteresis. This
output has programmable fault tolerance, which lets
the user to define the number of consecutive error
conditions that must occur before O.S. is activated.
The wide temperature and supply range and I2C
interface make the LM75A ideal for a number of
applications including base stations, electronic test
equipment, office electronics, personal computers,
and any other system in which thermal management
is critical to performance. The LM75A is available in
an SOIC-8 package and an VSSOP-8 package.
2 Applications
•
•
•
•
General System Thermal Management
Communications Infrastructure
Electronic Test Equipment
Environmental Monitoring
Device Information(1)
PART NUMBER
LM75A
PACKAGE
BODY SIZE (NOM)
SOIC (8)
4.90 mm × 3.91 mm
VSSOP (8)
3.00 mm × 3.00 mm
(1) For all available packages, see the orderable addendum at
the end of the datasheet.
Typical Application
+VS
100 nF (typ) unless mounted
close to processor
8
A0
Address
A1
(Set as desired)
A2
Interface
SDA
SCL
7
6
5
LM75
3
O.S.
To Processor
Interrupt Line
1
O.S. set to active low
IRUZLUH25¶GPXOWLSOH
interrupt line
2
4
GND
1
An IMPORTANT NOTICE at the end of this data sheet addresses availability, warranty, changes, use in safety-critical applications,
intellectual property matters and other important disclaimers. PRODUCTION DATA.
LM75A
SNOS808P – JANUARY 2000 – REVISED DECEMBER 2014
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Table of Contents
1
2
3
4
5
6
7
Features ..................................................................
Applications ...........................................................
Description .............................................................
Revision History.....................................................
Pin Configuration and Functions .........................
Specifications.........................................................
1
1
1
2
3
3
6.1
6.2
6.3
6.4
6.5
6.6
6.7
6.8
3
3
4
4
4
5
5
9
Absolute Maximum Ratings ......................................
ESD Ratings..............................................................
Recommended Operating Conditions.......................
Thermal Information ..................................................
Temperature-to-Digital Converter Characteristics.....
Digital DC Characteristics .........................................
I2C Digital Switching Characteristics.........................
Typical Characteristics ..............................................
Detailed Description ............................................ 10
7.1 Overview ................................................................. 10
7.2 Functional Block Diagram ....................................... 10
7.3
7.4
7.5
7.6
8
Feature Description.................................................
Device Functional Modes........................................
Programming...........................................................
Register Maps .........................................................
10
10
11
13
Application and Implementation ........................ 15
8.1 Application Information............................................ 15
8.2 Typical Applications ................................................ 15
8.3 System Examples ................................................... 16
9 Power Supply Recommendations...................... 18
10 Layout................................................................... 18
10.1 Layout Guidelines ................................................. 18
10.2 Layout Example .................................................... 19
11 Device and Documentation Support ................. 20
11.1 Trademarks ........................................................... 20
11.2 Electrostatic Discharge Caution ............................ 20
11.3 Glossary ................................................................ 20
12 Mechanical, Packaging, and Orderable
Information ........................................................... 20
4 Revision History
NOTE: Page numbers for previous revisions may differ from page numbers in the current version.
Changes from Revision O (May 2013) to Revision P
•
Added Pin Configuration and Functions section, ESD Ratings table, Feature Description section, Device Functional
Modes, Application and Implementation section, Power Supply Recommendations section, Layout section, Device
and Documentation Support section, and Mechanical, Packaging, and Orderable Information section .............................. 1
Changes from Revision N (May 2013) to Revision O
•
2
Page
Page
Changed layout of National Data Sheet to TI format ........................................................................................................... 16
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5 Pin Configuration and Functions
8-Pins
SOIC (D) and VSSOP (DGK) Packages
Top View
Pin Functions
PIN
NO.
NAME
1
SDA
2
DESCRIPTION
TYPICAL CONNECTION
I2C Serial Bi-Directional Data Line, Open
Drain
2
From Controller, tied to a pullup resistor or current source
SCL
I C Clock Input
From Controller, tied to a pullup resistor or current source
3
O.S.
Overtemperature Shutdown, Open Drain
Output
Pull–up Resistor, Controller Interrupt Line
4
GND
Power Supply Ground
Ground
5
A2
6
A1
User-Set I2C Address Inputs
Ground (Low, “0”) or +VS (High, “1”)
7
A0
8
+VS
Positive Supply Voltage Input
DC Voltage from 2.7 V to 5.5 V 100-nF bypass capacitor with 10-µF bulk
capacitance in the near vicinity
6 Specifications
6.1 Absolute Maximum Ratings
over operating free-air temperature range (unless otherwise noted) (1)
MIN
MAX
UNIT
Supply Voltage Pin (+VS)
−0.3
6.5
V
Voltage at A0, A1and A2 Pins
−0.3
(+VS + 0.3) and must be ≤ 6.5
V
Voltage at OS, SCL and SDA Pins
−0.3
6.5
V
Input Current at any Pin (2)
5
mA
Package Input Current (2)
20
mA
O.S. Output Sink Current
10
mA
O.S. Output Voltage
6.5
V
150
°C
Storage temperature, Tstg
(1)
(2)
–65
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.
When the input voltage (VI) at any pin exceeds the power supplies (VI < GND or VI > +VS) 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.
6.2 ESD Ratings
VALUE
Human-body model (HBM), per ANSI/ESDA/JEDEC JS-001
V(ESD)
(1)
(2)
Electrostatic discharge
(1)
UNIT
±2500
Charged-device model (CDM), per JEDEC specification JESD22C101 (2)
±1000
Machine model
±250
V
JEDEC document JEP155 states that 500-V HBM allows safe manufacturing with a standard ESD control process.
JEDEC document JEP157 states that 250-V CDM allows safe manufacturing with a standard ESD control process.
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6.3 Recommended Operating Conditions (1) (2)
Specified Temperature Range (TMIN to TMAX)
Supply Voltage Range (+VS) LM75A
(1)
(2)
MIN
MAX
UNIT
−55
125
°C
2.7
5.5
V
LM75A θJA (thermal resistance, junction-to-ambient) when attached to a printed circuit board with 2 oz. foil similar to the one shown in
Thermal Information is summarized in the table below the Operating Ratings table.
Reflow temperature profiles are different for lead-free and non-lead-free packages. Soldering process must comply with Reflow
Temperature Profile specifications. Refer to www.ti.com/packaging.(2)
6.4 Thermal Information
LM75A
THERMAL METRIC (1)
RθJA
(1)
Junction-to-ambient thermal resistance
D
DGK
8 PINS
8 PINS
200
250
UNIT
°C/W
For more information about traditional and new thermal metrics, see the IC Package Thermal Metrics application report, SPRA953.
6.5 Temperature-to-Digital Converter Characteristics
Unless otherwise noted, these specifications apply for: +VS = 2.7 to 5.5 Vdc for LM75AIM. TA = TJ = 25°C, unless otherwise
noted.
PARAMETER
TEST CONDITIONS
Accuracy
MIN
TYP (1)
TA = −25°C to +100°C
–55°C ≤ TJ ≤ 125°C
–2
2
TA = −55°C to +125°C
–55°C ≤ TJ ≤ 125°C
–3
3
Resolution
9
See (3)
Temperature Conversion Time
300
I2C Inactive
LM75A
0.28
I2C Inactive, –55°C ≤ TJ ≤ 125°C
0.5
Shutdown Mode, +VS = 3 V
4
Shutdown Mode, +VS = 5 V
6
UNIT
°C
Bits
100
See (3), –55°C ≤ TJ ≤ 125°C
Quiescent Current
MAX (2)
ms
mA
μA
μA
O.S. Output Saturation Voltage
IOUT = 4 mA, –55°C ≤ TJ ≤ 125°C
O.S. Delay
See (4), –55°C ≤ TJ ≤ 125°C
TOS Default Temperature
See (5)
80
°C
THYST Default Temperature
See (5)
75
°C
(1)
(2)
(3)
(4)
(5)
4
0.8
1
6
V
Conversion
Typicals are at TA = 25°C and represent most likely parametric norm.
Maximum values (limits) are ensured to AOQL (Average Outgoing Quality Level).
The conversion-time specification is provided to indicate how often the temperature data is updated. The LM75A can be accessed at
any time and reading the Temperature Register will yield result from the last temperature conversion. When the LM75A is accessed, the
conversion that is in process will be interrupted and it will be restarted after the end of the communication. Accessing the LM75A
continuously without waiting at least one conversion time between communications will prevent the device from updating the
Temperature Register with a new temperature conversion result. Consequently, the LM75A should not be accessed continuously with a
wait time of less than 300ms.
O.S. Delay is user programmable up to 6 “over limit” conversions before O.S. is set to minimize false tripping in noisy environments.
Default values set at power up.
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6.6 Digital DC Characteristics
Unless otherwise noted, these specifications apply for +VS = 2.7 to 5.5 Vdc for LM75AIM and LM75AIMM. TA = TJ = 25°C,
unless otherwise noted.
PARAMETER
VIN(1)
VIN(0)
TEST CONDITIONS
Logical “1” Input Voltage
Logical “0” Input Voltage
MIN
–55°C ≤ TJ ≤ 125°C
+VS × 0.7
–55°C ≤ TJ ≤ 125°C
−0.3
TYP (1)
MAX (2)
V
+VS + 0.3
V
V
+VS × 0.3
VIN = +VS
V
0.005
1.0
μA
−1.0
μA
IIN(1)
Logical “1” Input Current
IIN(0)
Logical “0” Input Current
CIN
All Digital Inputs
IOH
High Level Output
Current
Open drain leakage
VOL
Low Level Output Voltage
IOL = 3 mA, –55°C ≤
TJ ≤ 125°C
0.4
Output Fall Time
CL = 400 pF IO = 3
mA, –55°C ≤ TJ ≤
125°C
250
tOF
VIN = +VS, –55°C ≤
TJ ≤ 125°C
−0.005
VIN = 0 V
(1)
(2)
UNIT
VIN = 0 V, –55°C ≤
TJ ≤ 125°C
5
LM75A
pF
VOH = 5 V, –55°C ≤
TJ ≤ 125°C
μA
1
V
ns
Typicals are at TA = 25°C and represent most likely parametric norm.
Maximum values (limits) are ensured to AOQL (Average Outgoing Quality Level).
6.7 I2C Digital Switching Characteristics
Unless otherwise noted, these specifications apply for +VS = 2.7 to 5.5 Vdc for LM75AIM and LM75AIMM on output lines = 80
pF unless otherwise specified. TA = TJ = 25°C, unless otherwise noted.
PARAMETER
TEST CONDITIONS
MIN
TYP (1)
MAX (2) (3)
UNIT
t1
SCL (Clock) Period
–55°C ≤ TJ ≤ 125°C
2.5
ns
t2
Data in Set-Up Time to SCL High
–55°C ≤ TJ ≤ 125°C
100
ns
t3
Data Out Stable after SCL Low
–55°C ≤ TJ ≤ 125°C
0
ns
t4
SDA Low Set-Up Time to SCL Low (Start
Condition)
–55°C ≤ TJ ≤ 125°C
100
t5
SDA High Hold Time after SCL High (Stop
Condition)
–55°C ≤ TJ ≤ 125°C
100
tTIMEOUT
SDA Time Low for Reset of Serial
LM75A
Interface (4)
(1)
(2)
(3)
(4)
ns
ns
75
–55°C ≤ TJ ≤ 125°C
325
ms
Typicals are at TA = 25°C and represent most likely parametric norm.
Maximum values (limits) are ensured to AOQL (Average Outgoing Quality Level).
Timing specifications are tested at the bus input logic levels (Vin(0)=0.3XVA for a falling edge and Vin(1)=0.7XVA for a rising edge)
when the SCL and SDA edge rates are similar.
Holding the SDA line low for a time greater than tTIMEOUT will cause the LM75A to reset SDA to the IDLE state of the serial bus
communication (SDA set High).
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Figure 1. Timing Diagram
Figure 2. Temperature-to-Digital Transfer Function (Non-Linear Scale for Clarity)
Figure 3. Printed Circuit Board Used for Thermal Resistance Specifications
6
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Figure 4. I2C Timing Diagram
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Figure 5. I2C Timing Diagrams (Continued)
8
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6.8 Typical Characteristics
Figure 6. Accuracy vs Temperature (LM75A)
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7 Detailed Description
7.1 Overview
The LM75A temperature sensor incorporates a band-gap type temperature sensor and 9-bit ADC (sigma-delta
ADC). The temperature data output of the LM75A is available at all times via the I2C bus. If a conversion 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. The LM75A has
an integrated low-pass filter on both the SDA and the SCL line. These filters increase communications reliability
in noisy environments.
The LM75A also has a bus fault timeout feature. If the SDA line is held low for longer than tTIMEOUT (see
specification) the LM75A will reset to the IDLE state (SDA set to high impedance) and wait for a new start
condition. The TIMEOUT feature is not functional in Shutdown Mode.
7.2 Functional Block Diagram
+VS
8
Ð
1-Bit
D/A
TOS Set Point
Register
A0
A1
Set Point
Comparator
A2
Reset
Configuration
Register
Pointer
Register
5
THYST Set
Point Register
Product ID
Register
1
7
6
O.S.
Threshold
9-Bit Sigma-Delta ADC
Silicon Bandgap
Temperature
Sensor
3
Temperature
10-Bit
Digital
Decimation
Filter
Two-Wire Interface
2
SDA
SCL
4
GND
7.3 Feature Description
7.3.1 Digital Temperature Sensor
The LM75A is an industry-standard digital temperature sensor with an integrated sigma-delta ADC and I2C
interface. The LM75A provides 9-bit digital temperature readings with an accuracy of ±2°C from –25°C to 100°C
and ±3°C over –55°C to 125°C.
The LM75A operates with a single supply from +2.7 V to +5.5 V. Communication is accomplished over a 2-wire
interface which operates up to 400kHz. The LM75A has three address pins, allowing up to eight LM75A devices
to operate on the same 2-wire bus. The LM75A has a dedicated over-temperature output (O.S.) with
programmable limit and hysteresis. This output has programmable fault tolerance, which allows the user to
define the number of consecutive error conditions that must occur before O.S. is activated.
7.4 Device Functional Modes
In Comparator mode the O.S. Output behaves like a thermostat. The output becomes active when temperature
exceeds the TOS limit, and leaves the active state when the temperature drops below the THYST limit. In this mode
the O.S. output can be used to turn a cooling fan on, initiate an emergency system shutdown, or reduce system
clock speed. Shutdown mode does not reset O.S. state in a comparator mode.
In Interrupt mode exceeding TOS also makes O.S. active but O.S. will remain active indefinitely until reset by
reading any register via the I2C interface. Once O.S. has been activated by crossing TOS, then reset, it can be
activated again only by Temperature going below THYST. Again, it will remain active indefinitely until being reset
by a read. Placing the LM75A in shutdown mode also resets the O.S. Output.
10
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Device Functional Modes (continued)
The LM75A always powers up in a known state. The power up default conditions are:
• Comparator mode
• TOS = 80°C
• THYST = 75°C
• O.S. active low
• Pointer = “00”
When the supply voltage is less than about 1.7V, the LM75A is considered powered down. As the supply voltage
rises above the nominal 1.7V power up threshold, the internal registers are reset to the power up default values
listed above.
If the LM75A is not connected to the I2C bus on power up, it will act as a stand-alone thermostat with the power
up default conditions listed above. It is optional, but recommended, to connect the address pins (A2, A1, A0) and
the SCL and SDA pins together and to a 10k pullup resistor to +VS for better noise immunity. Any of these pins
may also be tied high separately through a 10-k pullup resistor.
7.5 Programming
7.5.1 I2C Bus Interface
The LM75A operates as a slave on the I2C bus, so the SCL line is an input (no clock is generated by the LM75A)
and the SDA line is a bi-directional serial data path. According to I2C bus specifications, the LM75A has a 7-bit
slave address. The four most significant bits of the slave address are hard wired inside the LM75A 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 +VS for a high, (1).
Therefore, the complete slave address is:
1
0
0
1
A2
A1
MSB
A0
LSB
These interrupt mode resets of O.S. occur only when LM75A is read or placed in shutdown. Otherwise, O.S. would
remain active indefinitely for any event.
Figure 7. O.S. Output Temperature Response Diagram
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7.5.2 Temperature Data Format
Temperature data can be read from the Temperature, TOS Set Point, and THYST Set Point registers; and written to
the TOS Set Point, and THYST Set Point registers. Temperature data is represented by a 9-bit, two's complement
word with an LSB (Least Significant Bit) equal to 0.5°C:
Temperature
Digital Output
Binary
Hex
+125°C
0 1111 1010
0FAh
+25°C
0 0011 0010
032h
+0.5°C
0 0000 0001
001h
0°C
0 0000 0000
000h
−0.5°C
1 1111 1111
1FFh
−25°C
1 1100 1110
1CEh
−55°C
1 1001 0010
192h
7.5.3 Shutdown Mode
Shutdown mode is enabled by setting the shutdown bit in the Configuration register via the I2C bus. Shutdown
mode reduces power supply current significantly. See specified quiescent current specification in the electrical
tables. In Interrupt mode O.S. is reset if previously set and is undefined in Comparator mode during shutdown.
The I2C interface remains active. Activity on the clock and data lines of the I2C bus may slightly increase
shutdown mode quiescent current. TOS, THYST, and Configuration registers can be read from and written to in
shutdown mode.
For the LM75A, the TIMEOUT feature is turned off in Shutdown Mode.
7.5.4 Fault Queue
A fault queue of up to 6 faults is provided to prevent false tripping of O.S. when the LM75A is used in noisy
environments. The number of faults set in the queue must occur consecutively to set the O.S. output.
7.5.5 Comparator and Interrupt Mode
As indicated in the O.S. Output Temperature Response Diagram, Figure 7, 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 LM75A.
7.5.6 O.S. Output
The O.S. output is an open-drain output and does not have an internal pullup. A “high” level will not be observed
on this pin until pullup current is provided from some external source, typically a pullup resistor. Choice of
resistor value depends on many system factors but, in general, the pullup resistor should be as large as possible.
This will minimize any errors due to internal heating of the LM75A. The maximum resistance of the pullup, based
on LM75A specification for High Level Output Current, to provide a 2-V high level, is 30 kΩ.
7.5.7 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 7. Active high simply inverts the polarity of the O.S. output.
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7.5.8 Internal Register Structure
SCL
2
I C Interface
SDA
Data
Address
Pointer Register
(Selects register for
communication)
Temperature
(Read-Only)
Pointer = 00000000
Configuration
(Read-Write)
Pointer = 00000001
TOS Set Point
(Read-Write)
Pointer = 00000011
THYST Set Point
(Read-Write)
Pointer = 00000010
Product ID
(Read-Only)
Pointer = 00000111
Figure 8. Register Structure
There are four data registers in the LM75A and an additional Product ID register selected by the Pointer register.
At power-up the Pointer is set to “000”; 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 LM75A, or placing the device in
shutdown mode, resets the O.S. output. All registers are read and write, except the Temperature register and the
LM75A's Product ID register, which are read-only.
A write to the LM75A will always include the address byte and the Pointer byte. A write to the Configuration
register requires one data byte, and the TOS and THYST registers require two data bytes.
Reading the LM75A 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 LM75A), 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 address 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 LM75A 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).
7.6 Register Maps
7.6.1 Pointer Register (Selects Which Registers Will Be Read From or Written to):
P7
P6
P5
P4
P3
0
0
0
0
0
P2
P1
P0
Register Select
P0-P1: Register Select:
P2
P1
P0
0
0
0
Temperature (Read-only) (Power-up default)
Register
0
0
1
Configuration (Read/Write)
0
1
0
THYST (Read/Write)
0
1
1
TOS (Read/Write)
1
1
1
Product ID Register
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P3–P7: Must be kept zero.
7.6.2 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 LSB = 0.5°C. Two's complement format.
7.6.3 Configuration Register (Read/Write):
D7
D6
D5
0
0
0
D4
D3
Fault Queue
D2
D1
D0
O.S. Polarity
Cmp/Int
Shutdown
Power up default is with all bits “0” (zero).
D0: Shutdown: When set to 1 the LM75A 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. Faults are determine at the end of a conversion. See specified temperature conversion time in the
electrical tables.
D4
D3
Number of Faults
0
0
1 (Power-up default)
0
1
2
1
0
4
1
1
6
D5–D7: These bits are used for production testing and must be kept zero for normal operation.
7.6.4 THYST and TOS Register (Read/Write):
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
75°C
D7–D15: THYST Or TOS Trip Temperature Data. Power up default is TOS = 80°C, THYST =
7.6.5 PRODID: Product ID Register (Read-Only) Pointer Address: 07h
D7
D6
D5
D4
D3
D2
D1
D0
1
0
1
0
0
0
0
1
D4--D7 Product Identification Nibble. Always returns Ah to uniquely identify this part as the LM75A.
D0--D3 Die Revision Nibble. Returns 1h to uniquely identify the revision level as one.
14
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8 Application and Implementation
NOTE
Information in the following applications sections is not part of the TI component
specification, and TI does not warrant its accuracy or completeness. TI’s customers are
responsible for determining suitability of components for their purposes. Customers should
validate and test their design implementation to confirm system functionality.
8.1 Application Information
The wide temperature and supply range and I2C interface make the LM75A ideal for a number of applications
including base stations, electronic test equipment, office electronics, personal computers, and any other system
where thermal management is critical to performance.
8.2 Typical Applications
8.2.1 Simple Fan Controller, Interface Optional
+VS
+12V
Optional but
Recommended
Pull-up
In Stand-alone
Mode
R3
10k
C1
100 nF
R1
10k
R2
10k
+12V/300 mA
Fan Motor
8
A0 7
A1 6
3 O.S.
A2 5
Q1
2N3904
Q2
NDP410A
series
LM75A
SDA 1
SCL 2
4
GND
When using the two-wire interface: program O.S. for active high and connect O.S. directly to Q2's gate.
Figure 9. Simple Fan Controller, Interface Optional
8.2.1.1 Design Requirements
The LM75A requires positive supply voltage of 2.7 V to 5.5 V to be applied between +Vs and GND. For best
results, bypass capacitors of 100 nF and 10 µF are recommended. Pullup resistors of 10 kΩ are required on SCL
and SDA.
8.2.1.2 Detailed Design Procedure
Accessing the conversion result of the LM75A consists of writing an address byte followed by retrieving the
corresponding number of data bytes. The first data byte is the most significant byte with the 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 LM75A 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). Temperature data is two's complement format and one LSB is
equivalent to 0.5°C.
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Typical Applications (continued)
8.2.1.3 Application Curve
Figure 10. Temperature Accuracy
8.3 System Examples
8.3.1 Simple Thermostat, Interface Optional
+ 5 VDC
Heater
Heater
Supply
Optional but
Recommended
Pull-up In
Stand-alone
Mode
C1
100 nF
R2
10k
8
R1
+VS 10k
K1
5V
Relay
D1
1N4001
A0 7
A1 6
A2 5
LM75A
3
O.S.
Q1
2N2222A
SDA 1
SCL 2
4
GND
Figure 11. Simple Thermostat, Interface Optional
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System Examples (continued)
8.3.2 Temperature Sensor with Loudmouth Alarm (Barking Watchdog)
+VS
Optional but
Recommended
Pull-up
In Stand-alone
Mode
R3
10k
C6
100 nF
R1
10k
8
A0 7
A1 6
3
A2 5
LM75A
SDA 1
SCL 2
4
GND
SHUTDOWN Vo2
BYPASS
C1
100 nF
C2
100 nF
+IN
-IN
GND
VDD
LM4861M Vo1
R5 200k
O.S.
C3
6.8 nF
C4
6.8 nF
C5
6.8 nF
R2
10k
R3
10k
R4
10k
Figure 12. Temperature Sensor with Loudmouth Alarm (Barking Watchdog)
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9 Power Supply Recommendations
The LM75A is specified for operation from 2.7 V to 5.5 V. Place 100-nF and 10-µF capacitors close to +Vs in
order to reduce errors coupling in from noisy or high impedance supplies.
10 Layout
10.1 Layout Guidelines
To achieve the expected results when measuring temperature with an integrated circuit temperature sensor like
the LM75A, it is important to understand that the sensor measures its own die temperature. For the LM75A, the
best thermal path between the die and the outside world is through the LM75A's pins. In the VSSOP-8 package,
the GND pin is directly connected to the die, so the GND pin provides the best thermal path. If the other pins are
at different temperatures (unlikely, but possible), they will affect the die temperature, but not as strongly as the
GND pin. In the SOIC-8 package, none of the pins is directly connected to the die, so they will all contribute
similarly to the die temperature. Because the pins represent a good thermal path to the LM75A die, the LM75A
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 LM75A 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.
In probe-type applications, the LM75A 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 LM75A 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 LM75A or its
connections.
10.1.1 Digital Noise Issues
The LM75A features an integrated low-pass filter on both the SCL and the SDA digital lines to mitigate the
effects of bus noise. Although this filtering makes the LM75A communication robust in noisy environments, good
layout practices are always recommended. Minimize noise coupling by keeping digital traces away from
switching power supplies. Also, ensure that digital lines containing high-speed data communications cross at
right angles to the SDA and SCL lines. Excessive noise coupling into the SDA and SCL lines on the
LM75A—specifically noise with amplitude greater than 400 mVpp (the LM75A’s typical hysteresis), overshoot
greater than 300mV above +Vs, and undershoot more than 300 mV below GND—may prevent successful serial
communication with the LM75A. Serial bus no-acknowledge is the most common symptom, causing unnecessary
traffic on the bus. Although the serial bus maximum frequency of communication is only 400 kHz, care must be
taken to ensure proper termination within a system with long printed circuit board traces or multiple parts on the
bus.
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10.2 Layout Example
Figure 13. Printed Circuit Board Used for Thermal Resistance Specifications
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11 Device and Documentation Support
11.1 Trademarks
All trademarks are the property of their respective owners.
11.2 Electrostatic Discharge Caution
These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam
during storage or handling to prevent electrostatic damage to the MOS gates.
11.3 Glossary
SLYZ022 — TI Glossary.
This glossary lists and explains terms, acronyms, and definitions.
12 Mechanical, Packaging, and Orderable Information
The following pages include mechanical, packaging, and orderable information. This information is the most
current data available for the designated devices. This data is subject to change without notice and revision of
this document. For browser-based versions of this data sheet, refer to the left-hand navigation.
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PACKAGE OPTION ADDENDUM
www.ti.com
10-Dec-2020
PACKAGING INFORMATION
Orderable Device
Status
(1)
Package Type Package Pins Package
Drawing
Qty
Eco Plan
(2)
Lead finish/
Ball material
MSL Peak Temp
Op Temp (°C)
Device Marking
(3)
(4/5)
(6)
LM75AIM/NOPB
ACTIVE
SOIC
D
8
95
RoHS & Green
SN
Level-1-260C-UNLIM
-55 to 125
LM75
AIM
LM75AIMM/NOPB
ACTIVE
VSSOP
DGK
8
1000
RoHS & Green
SN
Level-1-260C-UNLIM
-55 to 125
T00A
LM75AIMME/NOPB
ACTIVE
VSSOP
DGK
8
250
RoHS & Green
SN
Level-1-260C-UNLIM
-55 to 125
T00A
LM75AIMMX/NOPB
ACTIVE
VSSOP
DGK
8
3500
RoHS & Green
SN
Level-1-260C-UNLIM
-55 to 125
T00A
LM75AIMX/NOPB
ACTIVE
SOIC
D
8
2500
RoHS & Green
SN
Level-1-260C-UNLIM
-55 to 125
LM75
AIM
(1)
The marketing status values are defined as follows:
ACTIVE: Product device recommended for new designs.
LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.
NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design.
PREVIEW: Device has been announced but is not in production. Samples may or may not be available.
OBSOLETE: TI has discontinued the production of the device.
(2)
RoHS: TI defines "RoHS" to mean semiconductor products that are compliant with the current EU RoHS requirements for all 10 RoHS substances, including the requirement that RoHS substance
do not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, "RoHS" products are suitable for use in specified lead-free processes. TI may
reference these types of products as "Pb-Free".
RoHS Exempt: TI defines "RoHS Exempt" to mean products that contain lead but are compliant with EU RoHS pursuant to a specific EU RoHS exemption.
Green: TI defines "Green" to mean the content of Chlorine (Cl) and Bromine (Br) based flame retardants meet JS709B low halogen requirements of
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