LM73
LM73 2.7V, SOT-23, 11-to-14 Bit Digital Temperature Sensor with 2-Wire
Interface
Literature Number: SNIS141D
LM73
May 13, 2009
2.7V, SOT-23, 11-to-14 Bit Digital Temperature Sensor with
2-Wire Interface
General Description
The LM73 is an integrated, digital-output temperature sensor
featuring an incremental Delta-Sigma ADC with a two-wire
interface that is compatible with the SMBus and I2C® inter-
faces. The host can query the LM73 at any time to read
temperature. Available in a 6-pin SOT-23 package, the LM73
occupies very little board area while operating over a wide
temperature range (-40°C to 150°C) and providing ±1.0°C
accuracy from -10°C to 80°C. The user can optimize between
the conversion time and the sensitivity of the LM73 by pro-
gramming it to report temperature in any of four different
resolutions. Defaulting to 11-bit mode (0.25°C/LSB), the
LM73 measures temperature in a maximum time of 14 ms,
making it ideal for applications that require temperature data
very soon after power-up. In its maximum resolution, 14-bit
mode (0.03125°C/LSB), the LM73 is optimized to sense very
small changes in temperature.
A single multi-level address line selects one of three unique
device addresses. An open-drain ALERT output goes active
when the temperature exceeds a programmable limit. Both
the data and clock lines are filtered for excellent noise toler-
ance and reliable communication. Additionally, a time-out
feature on the clock and data lines causes the LM73 to auto-
matically reset these lines if either is held low for an extended
time, thus exiting any bus lock-up condition without processor
intervention.
Applications
■Portable Electronics
■Notebook Computers
■Automotive
■System Thermal Management
■Office Electronics
Key Specifications
■ Supply Voltage 2.7V to 5.5V
■ Supply Current operating 320 µA (typ)
495 µA (max)
shutdown 8 µA (max)
1.9 µA (typ)
■ Temperature −10°C to 80°C ±1.0°C (max)
Accuracy −25°C to 115°C ±1.5°C (max)
−40°C to 150°C ±2.0°C (max)
■ Resolution 0.25°C to
0.03125°C
■ Conversion Time 11-bit (0.25°C) 14 ms (max)
14-bit (0.03125°C) 112 ms (max)
Features
■Single address pin offers choice of three selectable
addresses per version for a total of six possible addresses.
■SMBus and I2C-compatible two-wire interface
■Supports 400 kHz operation
■Shutdown mode with one-shot feature available for very
low average power consumption
■Programmable digital temperature resolution from 11 bits
to 14 bits.
■Fast conversion rate ideal for quick power up and
measuring rapidly changing temperature
■Open-drain ALERT output pin goes active when
temperature is above a programmed temperature limit
■Very stable, low-noise digital ouput.
■UL Recognized Component
Typical Application
20147803
I2C is a registered trademark of Philips Electronics N.V. Corporation
© 2009 National Semiconductor Corporation 201478 www.national.com
LM73 2.7V, SOT-23, 11-to-14 Bit Digital Temperature Sensor with 2-Wire Interface
Simplified Block Diagram
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Connection Diagram
SOT23-6
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TOP VIEW
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LM73
Ordering Information
Part Number Package
Marking
NS Package
Number
Transport
Media
SMBus Device Address
Address Pin Device Address
LM73CIMK-0 T730 MK06A
(Thin SOT23-6)
1000 Units on Tape
and Reel
Float
Ground
VDD
1001 000
1001 001
1001 010
LM73CIMKX-0 T730 MK06A
(Thin SOT23-6)
3000 Units on Tape
and Reel
Float
Ground
VDD
1001 000
1001 001
1001 010
LM73CIMK-1 T731 MK06A
(Thin SOT23-6)
1000 Units on Tape
and Reel
Float
Ground
VDD
1001 100
1001 101
1001 110
LM73CIMKX-1 T731 MK06A
(Thin SOT23-6)
3000 Units on Tape
and Reel
Float
Ground
VDD
1001 100
1001 101
1001 110
Note 1: Available in RoHS-compliant packages. More details at www.national.com.
Pin Descriptions
Label Pin # Type Equivalent Circuit Function
ADDR 1 CMOS Logic
Input
(three levels)
Address Select Input: One of three device
addresses is selected by connecting to ground,
left floating, or connecting to VDD.
GND 2 Ground Ground
VDD 3 Power Supply Voltage
SMBCLK 4 CMOS Logic
Input
Serial Clock: SMBus clock signal. Operates up
to 400 kHz. Low-pass filtered.
ALERT 5 Open-Drain
Output
Digital output which goes active whenever the
measured temperature exceeds a
programmable temperature limit.
SMBDAT 6 Open-Drain
Input/Output
Serial Data: SMBus bi-directional data signal
used to transfer serial data synchronous to the
SMBCLK. Low-pass filtered.
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LM73
Absolute Maximum Ratings (Note 2)
Supply Voltage −0.3 V to 6.0 V
Voltage at SMBCLK and
SMBDAT pins −0.3 V to 6.0 V
Voltage at All Other Pins −0.3 V to
(VDD + 0.5 V) and ≤ 6.0 V
Input Current at Any Pin (Note 3) ±5 mA
Storage Temperature −65°C to +150°C
ESD Susceptibility (Note 5)
Human Body Model 2000 V
Machine Model 200 V
Soldering process must comply with National
Semiconductor's Reflow Temperature Profile specifications.
Refer to www.national.com/packaging. (Note 4)
Operating Ratings
(Note 2)
Specified Temperature Range TMIN ≤ TA ≤ TMAX
−40°C ≤ TA ≤ +150°C
Supply Voltage Range (VDD)+2.7V to +5.5V
Temperature-to-Digital Converter Characteristics
Unless otherwise noted, these specifications apply for VDD = 2.7V to 5.5V. Boldface limits apply for TA = TJ =TMIN to TMAX; all
other limits TA = TJ = +25°C, unless otherwise noted. TA is the ambient temperature. TJ is the junction temperature.
Parameter Conditions Typical
(Note 6)
LM73C
Units (Limit)
Limits
(Note 7)
Accuracy (Note 8) VDD = 2.7V
to
VDD = 4.5V
TA = −10°C to 80°C ±1.0 °C (max)
TA = −25°C to 115°C ±1.5 °C (max)
TA = −40°C to 150°C ±2.0 °C (max)
VDD > 4.5V
to
VDD = 5.5V
TA = −10°C to 80°C ±1.5 °C (max)
TA = −25°C to 115°C ±2.0 °C (max)
TA = −40°C to 150°C ±2.5 °C (max)
Resolution RES1 Bit = 0, RES0 Bit = 0 11 Bits
0.25 °C/LSB
RES1 Bit = 0, RES0 Bit = 1 12 Bits
0.125 °C/LSB
RES1 Bit = 1, RES0 Bit = 0 13 Bits
0.0625 °C/LSB
RES1 Bit = 1, RES0 Bit = 1 14 Bits
0.03125 °C/LSB
Temperature Conversion
Time (Note 9)
RES1 Bit = 0, RES0 Bit = 0 10.1 14 ms (max)
RES1 Bit = 0, RES0 Bit = 1 20.2 28 ms (max)
RES1 Bit = 1, RES0 Bit = 0 40.4 56 ms (max)
RES1 Bit = 1, RES0 Bit = 1 80.8 112 ms (max)
Quiescent Current Continuous Conversion Mode, SMBus inactive 320 495 µA (max)
Shutdown, bus-idle timers on 120 175 µA (max)
Shutdown, bus-idle timers off 1.9 8µA (max)
Power-On Reset Threshold Measured on VDD input, falling edge 0.9 V (min)
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LM73
Logic Electrical Characteristics
DIGITAL DC CHARACTERISTICS
Unless otherwise noted, these specifications apply for VDD = 2.7V to 5.5V. Boldface limits apply for TA = TJ = TMIN to TMAX; all
other limits TA = TJ = +25°C, unless otherwise noted. TA is the ambient temperature. TJ is the junction temperature.
Symbol Parameter Conditions Typical Limits Units
(Note 6) (Note 7) (Limit)
SMBDAT, SMBCLK INPUTS
VIH Logical “1” Input Voltage 0.7*VDD V (min)
VIL Logical “0” Input Voltage 0.3*VDD V (max)
VIN;HYST SMBDAT and SMBCLK Digital Input
Hysteresis
0.07*VDD V
IIH Logical “1” Input Current VIN = VDD 0.01 2µA (max)
IIL Logical “0” Input Current VIN = 0 V –0.01 –2µA (max)
CIN Input Capacitance 5 pF
SMBDAT, ALERT OUTPUTS
IOH High Level Output Current VOH = VDD 0.01 2µA (max)
VOL SMBus Low Level Output Voltage IOL = 3 mA 0.4 V (max)
ADDRESS INPUT
VIH;ADDRESS Address Pin High Input Voltage VDD minus 0.100 V (min)
VIL;ADDRESS Address Pin Low Input Voltage 0.100 V (max)
IIH; ADDRESS Address Pin High Input Current VIN = VDD 0.01 2µA (max)
IIL;ADDRESS Address Pin Low Input Current VIN = 0 V –0.01 –2 µA (max)
SMBus DIGITAL SWITCHING CHARACTERISTICS
Unless otherwise noted, these specifications apply for VDD = +2.7 V to +5.5 V, CL (load capacitance) on output lines = 400 pF.
Boldface limits apply for TA = TJ = TMIN to TMAX; all other limits TA = TJ = +25°C, unless otherwise noted.
Symbol Parameter Conditions Typical Limits Units
(Note 6) (Note 7) (Limit)
fSMB SMBus Clock Frequency No minimum clock frequency
if Time-Out feature is
disabled.
400 kHz (max)
tLOW SMBus Clock Low Time 300 ns (min)
tHIGH SMBus Clock High Time 300 ns (min)
tF;SMBO Output Fall Time (Note 10) CL = 400 pF
IPULL-UP ≤ 3 mA
250 ns (max)
tTIMEOUT SMBDAT and SMBCLK Time Low for Reset of
Serial Interface (Note 11)
15
45
ms (min)
ms (max)
tSU;DAT Data In Setup Time to SMBCLK High 100 ns (min)
tHD;DATI Data Hold Time: Data In Stable after SMBCLK
Low
0ns (min)
tHD;DATO Data Hold Time: Data Out Stable after SMBCLK
Low
30 ns (min)
tHD;STA Start Condition SMBDAT Low to SMBCLK Low
(Start condition hold before the first clock falling
edge)
60 ns (min)
tSU;STO Stop Condition SMBCLK High to SMBDAT Low
(Stop Condition Setup)
50 ns (min)
tSU;STA SMBus Repeated Start-Condition Setup Time,
SMBCLK High to SMBDAT Low
50 ns (min)
tBUF SMBus Free Time Between Stop and Start
Conditions
1.2 µs (min)
tPOR Power-On Reset Time (Note 12) 1ms (max)
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LM73
SMBus Communication
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Note 2: 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 3: When the input voltage (VI) at any pin exceeds the power supplies (VI < GND or VI > VDD), the current at that pin should be limited to 5 mA.
Note 4: Reflow temperature profiles are different for lead-free and non-lead-free packages.
Note 5: Human body model, 100 pF discharged through a 1.5 kΩ resistor. Machine model, 200 pF discharged directly into each pin.
Note 6: Typicals are at TA = 25°C and represent most likely parametric norm.
Note 7: Limits are guaranteed to National's AOQL (Average Outgoing Quality Level).
Note 8: Local temperature accuracy does not include the effects of self-heating. The rise in temperature due to self-heating is the product of the internal power
dissipation of the LM73 and the thermal resistance.
Note 9: This specification is provided only to indicate how often temperature data is updated. The LM73 can be read at any time without regard to conversion
state (and will yield last conversion result).
Note 10: The output fall time is measured from (VIH;MIN + 0.15V) to (VIL;MAX - 0.15V).
Note 11: Holding the SMBDAT and/or SMBCLK lines Low for a time interval greater than tTIMEOUT will reset the LM73's SMBus state machine, setting SMBDAT
and SMBCLK pins to a high impedance state.
Note 12: Represents the time from VDD reaching the power-on-reset level to the LM73 communications being functional. After an additional time equal to one
temperature conversion time, valid temperature will be available in the Temperature Register.
Note 13: A write to an invalid pointer address is not allowed. If the master writes an invalid address to the Pointer Register, (1) the LM73 will not acknowledge
the address and (2) the Pointer Register will continue to contain the last value stored in it.
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LM73
Typical Performance Characteristics
Accuracy vs. Temperature
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Operating Current vs. Temperature
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Shutdown Current vs.Temperature
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Typical Output Noise
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LM73
1.0 Functional Description
The LM73 is a digital temperature sensor that senses the
temperature of its die using a sigma-delta analog-to-digital
converter and stores the temperature in the Temperature
Register. The LM73's 2-wire serial interface is compatible with
SMBus 2.0 and I2C. Please see the SMBus 2.0 specification
for a detailed description of the differences between the I2C
bus and SMBus.
The temperature resolution is programmable, allowing the
host system to select the optimal configuration between sen-
sitivity and conversion time. The LM73 can be placed in
shutdown to minimize power consumption when temperature
data is not required. While in shutdown, a 1-shot conversion
mode allows system control of the conversion rate for ultimate
flexibility.
The LM73 features the following registers. See Section 2.0
for a complete list of the pointer address, content, and reset
state of each register.
1. Pointer Register
2. Temperature Register
3. Configuration Register
4. THIGH Register
5. TLOW Register
6. Control/Status Register
7. Identification Register
1.1 POWER-ON RESET
The power-on reset (POR) state is the point at which the sup-
ply voltage rises above the power-on reset threshold (speci-
fied in the electrical specifications table), generating an
internal reset. Each of the registers contains a defined value
upon POR and this data remains there until any of the follow-
ing occurs:
1. The first temperature conversion is completed, causing the
Temperature Register and various status bits to be updated
internally, depending on the value of the measured tempera-
ture.
2. The master writes different data to any Read/Write (R/W)
bits, or
3. The LM73 is powered down.
1.2 ONE-SHOT CONVERSION
The LM73 features a one-shot conversion bit, which is used
to initiate a single conversion and comparison cycle when the
LM73 is in shutdown mode. While the LM73 is in shutdown
mode, writing a "1" to the One-Shot bit in the Configuration
Register will cause the LM73 to perform a single temperature
conversion and update the Temperature Register and the af-
fected status bits. Operating the LM73 in this one-shot mode
allows for extremely low average-power consumption, mak-
ing it ideal for low-power applications.
When the One-Shot bit is set, the LM73 initiates a tempera-
ture conversion. After this initiation, but before the completion
of the conversion and resultant register updates, the LM73 is
in a "one-shot" state. During this state, the Data Available
(DAV) flag in the Control/Status register is "0" and the Tem-
perature Register contains the value 8000h (-256°C). All other
registers contain the data that was present before initiating
the one-shot conversion. After the temperature measurement
is complete, the DAV flag will be set to "1" and the temperature
register will contain the resultant measured temperature.
1.3 TEMPERATURE DATA FORMAT
The resolution of the temperature data and the size of the data
word are user-selectable through bits RES1 and RES0 in the
Control/Status Register. By default, the LM73 temperature
stores the measured temperature in an 11-bit (10 bits plus
sign) word with one least significant bit (LSB) equal to 0.25°
C. The maximum word size is 14 bits (13-bits plus sign) with
a resolution of 0.03125 °C/LSB.
CONTROL BIT DATA FORMAT
RES1 RES0 WORD SIZE RESOLUTION
0 0 11 bits 0.25 °C/LSB
0 1 12 bits 0.125 °C/LSB
1 0 13 bits 0.0625 °C/LSB
1 1 14 bits 0.03125 °C/LSB
The temperature data is reported in 2's complement format.
The word is stored in the 16-bit Temperature Register and is
left justified in this register. Unused temperature-data bits are
always reported as "0".
11-bit (10-bit plus Sign)
Temperature Digital Output
Binary Hex
+150°C 0100 1011 0000 0000 4B00h
+25°C 0000 1100 1000 0000 0C80h
+1°C 0000 0000 1000 0000 0080h
+0.25°C 0000 0000 0010 0000 0020h
0°C 0000 0000 0000 0000 0000h
−0.25°C 1111 1111 1110 0000 FFE0h
−1°C 1111 1111 1000 0000 FF80h
−25°C 1111 0011 1000 0000 F380h
−40°C 1110 1100 0000 0000 EC00h
12-bit (11-bit plus Sign)
Temperature Digital Output
Binary Hex
+150°C 0100 1011 0000 0000 4B00h
+25°C 0000 1100 1000 0000 0C80h
+1°C 0000 0000 1000 0000 0080h
+0.125°C 0000 0000 0001 0000 0010h
0°C 0000 0000 0000 0000 0000h
−0.125°C 1111 1111 1111 0000 FFF0h
−1°C 1111 1111 1000 0000 FF80h
−25°C 1111 0011 1000 0000 F380h
−40°C 1110 1100 0000 0000 EC00h
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LM73
13-bit (12-bit plus Sign)
Temperature Digital Output
Binary Hex
+150°C 0100 1011 0000 0000 4B00h
+25°C 0000 1100 1000 0000 0C80h
+1°C 0000 0000 1000 0000 0080h
+0.0625°C 0000 0000 0000 1000 0008h
0°C 0000 0000 0000 0000 0000h
−0.0625°C 1111 1111 1111 1000 FFF8h
−1°C 1111 1111 1000 0000 FF80h
−25°C 1111 0011 1000 0000 F380h
−40°C 1110 1100 0000 0000 EC00h
14-bit (13-bit plus Sign)
Temperature Digital Output
Binary Hex
+150°C 0100 1011 0000 0000 4B00h
+25°C 0000 1100 1000 0000 0C80h
+1°C 0000 0000 1000 0000 0080h
+0.03125°C 0000 0000 0000 0100 0004h
0°C 0000 0000 0000 0000 0000h
−0.03125°C 1111 1111 1111 1100 FFFCh
−1°C 1111 1111 1000 0000 FF80h
−25°C 1111 0011 1000 0000 F380h
−40°C 1110 1100 0000 0000 EC00h
1.4 SMBus INTERFACE
The LM73 operates as a slave on the SMBus. The SMBDAT
line is bidirectional. The SMBCLK line is an input only. The
LM73 never drives the SMBCLK line and it does not support
clock stretching.
The LM73 uses a 7-bit slave address. It is available in two
versions. Each version can be configured for one of three
unique slave addresses, for a total of six unique address.
Part Number Address Pin Device
Address
LM73-0 Float
Ground
VDD
1001 000
1001 001
1001 010
LM73-1 Float
Ground
VDD
1001 100
1001 101
1001 110
The SMBDAT output is an open-drain output and does not
have internal pull-ups. A “high” level will not be observed on
this pin until pull-up current is provided by 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 without effecting the
SMBus desired data rate. This will minimize any internal tem-
perature reading errors due to internal heating of the LM73.
The LM73 features an integrated low-pass filter on both the
SMBCLK and the SMBDAT line. These filters increase com-
munications reliability in noisy environments.
If either the SMBCLK or SMBDAT line is held low for a time
greater than tTIMEOUT (see Logic Electrical Characteristics for
the value of tTIMEOUT), the LM73 state machine will reset to the
SMBus idle state, releasing the data line. Once the SMBDAT
is released high, the master may initiate an SMBus start.
1.5 ALERT FUNCTION
The ALERT output is an over-temperature indicator. At the
end of every temperature conversion, the measured temper-
ature is compared to the value in the THIGH Register. If the
measured temperature exceeds the value stored in THIGH, the
ALERT output goes active (see Figure 1). This over-temper-
ature condition will also cause the ALRT_STAT bit in the
Control/Status Register to change value (this bit mirrors the
logic level of the ALERT pin).
The ALERT pin and the ALRT_STAT bit are cleared when any
of the following occur:
1. The measured temperature falls below the value stored
in the TLOW Register
2. A "1" is written to the ALERT Reset bit in the
Configuration Register
3. The master resets it through an SMBus Alert Response
Address (ARA) procedure
If ALERT has been cleared by the master writing a "1" to the
ALERT Reset bit, while the measured temperature still ex-
ceeds the THIGH setpoint, ALERT will go active again after the
completion of the next temperature conversion.
Each temperature reading is associated with a Temperature
High (THI) and a Temperature Low (TLOW) flag in the Con-
trol/Status Register. A digital comparison determines whether
that reading is above the THIGH setpoint or below the TLOW
setpoint. If so, the corresponding flag is set. All digital com-
parisons to the THIGH, and TLOW values are based on an 11-
bit temperature comparison. Regardless of the resolution
setting of the LM73, the lower three temperature LSBs will not
affect the state of the ALERT output, THI flag, and TLOW flag.
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FIGURE 1. ALERT Temperature Response cleared when
temperature crosses TLOW
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LM73
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FIGURE 2. ALERT Temperature Response cleared by
writing a "1" to the ALERT Reset Bit.
1.6 COMMUNICATING WITH THE LM73
The data registers in the LM73 are selected by the Pointer
Register. At power-up the Pointer Register is set to “00h”, the
location for the Temperature Register. The Pointer Register
latches the last location it was set to. Note that all Pointer
Register bits are decoded; any incorrect pointer values will
not be acknowledged and will not be stored in the Pointer
Register (Note 13).
A Write to the LM73 will always include the address byte and
the pointer byte.
A Read from the LM73 can take place either of two ways:
1. If the location latched in the Pointer Register is correct
(that is, the Pointer Register is pre-set prior to the read),
then the read can simply consist of an address byte,
followed by retrieving the data byte. Most of the time it is
expected that the Pointer Register will point to
Temperature Registers because that will be the data
most frequently read from the LM73.
2. If the Pointer Register needs to be set, then an address
byte, pointer byte, repeat start, and another address byte
will accomplish a read.
The data byte is read out of the LM73 by the most significant
bit first. At the end of a read, the LM73 can accept either an
Acknowledge or No Acknowledge bit from the Master. No Ac-
knowledge is typically used as a signal to the slave that the
Master has read its last byte.
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(a) Typical Read from a 2-Byte Register with Preset Pointer
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(b) Typical Pointer Set Followed by Immediate Read of a 2-Byte Register
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(c) Typical Read from a 1-Byte Register with Preset Pointer
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LM73
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(d) Typical Pointer Set Followed by Immediate Read of a 1-Byte Register.
FIGURE 3. Reading from the LM73
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(a) Typical 1-Byte Write
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(b) Typical 2-Byte Write
FIGURE 4. Writing to the LM73
1.7 SHUTDOWN MODE
Shutdown Mode is enabled by writing a “1” to the Full Power
Down Bit, Bit 7 of the Configuration Register, and holding it
high for at least the specified maximum conversion time at the
existing temperature resolution setting. (see Temperature
Conversion Time specifications under the Temperature-to-
Digital Characteristics section). For example, if the LM73 is
set for 12-bit resolution before shutdown, then Bit 7 of the
Configuration register must go high and stay high for the
specified maximum conversion time for 12-bits resolution.
The LM73 will always finish a temperature conversion and
update the temperature registers before shutting down.
Writing a “0” to the Full Power Down Bit restores the LM73 to
normal mode. The user should wait at least the specified
maximum conversion time, at the existing resolution setting,
before accurate data appears in the temperature register.
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LM73
2.0 LM73 Registers
The LM73's internal registers are selected by the Pointer register. The Pointer register latches the last location that it was set to.
The pointer register and all internal registers are described below. All registers reset at device power up.
2.1 POINTER REGISTER
The diagram below shows the Pointer Register, the six internal registers to which it points, and their associated pointer addresses.
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P7 P6 P5 P4 P3 P2 P1 P0
0 0 0 0 0 Register Select
Bits Name Description
7:3 Not Used Must write zeros only.
2:0 Register Select Pointer address. Points to desired register.
See table below.
P2 P1 P0 REGISTER (Note 13)
0 0 0 Temperature
0 0 1 Configuration
0 1 0 THIGH
0 1 1 TLOW
1 0 0 Control / Status
1 1 1 Identification
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LM73
2.2 TEMPERATURE DATA REGISTER
Pointer Address 00h (Read Only)
Reset State: 7FFCh (+255.96875°C)
One-Shot State: 8000h (-256°C)
D15 D14 D13 D12 D11 D10 D9 D8
SIGN 128°C 64°C 32°C 16°C 8°C 4°C 2°C
D7 D6 D5 D4 D3 D2 D1 D0
1°C 0.5°C 0.25°C 0.125°C 0.0625°C 0.03125°C reserved reserved
Bits Name Description
15:2 Temperature Data Represents the temperature that was measured by the most recent temperature conversion. On
Power-up, this data is invalid until the Data Available (DAV) bit in the Control/Status register is
high (after the completion of the first temperature conversion). The resolution is user-
progammable from 11-bit resolution (0.25°C/LSB) through 14-bit resolution (0.03125°C/LSB).
The desired resolution is programmed with bits 5 and 6 of the Control/Status register.
1:0 Not Used Return zeros upon read.
2.3 CONFIGURATION REGISTER
Pointer Address 01h (R/W)
Reset State: 40h
D7 D6 D5 D4 D3 D2 D1 D0
PD reserved ALRT EN ALRT POL ALRT RST ONE SHOT reserved
Bits Name Description
7 Full Power Down Writing a "1" to this bit and holding it high for at least the specified maximum conversion time, at the
existing temperature resolution setting, puts the LM73 in shutdown mode for power conservation.
Writing a "0" to this bit restores the LM73 to normal mode. Waiting one specified maximum conversion
time for the existing resolution setting assures accurate data in the temperature register.
6 reserved User must write only a 1 to this bit
5 ALERT Enable A 0 in this location enables the ALERT output. A 1 disables it. This bit also controls the ALERT Status
bit (the Control/Status Register, Bit 3) since that bit reflects the state of the Alert pin.
4 ALERT Polarity When set to 1, the ALERT pin and ALERT Status bit are active-high. When 0, it is active-low.
3 ALERT Reset Writing a 1 to this bit resets the ALERT pin and the ALERT Status bit. It will always be 0 when read.
2 One Shot When in shutdown mode (Bit 7 is 1), initiates a single temperature conversion and update of the
temperature register with new temperature data. Has no effect when in continuous conversion mode
(i.e., when Bit 7 is 0). Always returns a 0 when read.
1:0 Reserved User must write only a 0 to these bits.
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LM73
2.4 THIGH UPPER-LIMIT REGISTER
Pointer Address 02h (R/W)
Reset State: 7FE0h (+255.75°C)
D15 D14 D13 D12 D11 D10 D9 D8
SIGN 128°C 64°C 32°C 16°C 8°C 4°C 2°C
D7 D6 D5 D4 D3 D2 D1 D0
1°C 0.5°C 0.25°C reserved
Bits Name Description
15:5 Upper-Limit
Temperature
If the measured temperature that is stored in this register exceeds this user-programmable upper
temperature limit, the ALERT pin will go active and the THIGH flag in the Control/Status register
will be set to 1. Two's complement format.
4:0 Reserved Returns zeros upon read. Recommend writing zeros only in these bits.
2.5 TLOW LOWER-LIMIT REGISTER
Pointer Address 03h (R/W)
Reset State: 8000h (–256°C)
D15 D14 D13 D12 D11 D10 D9 D8
SIGN 128°C 64°C 32°C 16°C 8°C 4°C 2°C
D7 D6 D5 D4 D3 D2 D1 D0
1°C 0.5°C 0.25°C reserved
Bits Name Description
15:5 Lower-Limit
Temperature
If the measured temperature that is stored in the temperature register falls below this user-
programmable lower temperature limit, the ALERT pin will be deactivated and the TLOW flag in
the Control/Status register will be set to 1. Two's complement format.
4:0 Reserved Returns zeros upon read. Recommend writing zeros only in these bits.
2.6 CONTROL/STATUS REGISTER
Pointer Address 04h (R/W)
Reset State: 08h
D7 D6 D5 D4 D3 D2 D1 D0
TO_DIS RES1 RES0 reserved ALRT_STAT THI TLOW DAV
Bits Name Description
7 Time-Out Disable Disable the time-out feature on the SMBDAT and SMBCLK lines if set to 1. Setting this bit turns off
the bus-idle timers, enabling the LM73 to operate at lowest shutdown current.
6:5 Temperature
Resolution
Selects one of four user-programmable temperature data resolutions
00: 0.25°C/LSB, 11-bit word (10 bits plus Sign)
01: 0.125°C/LSB, 12-bit word (11 bits plus Sign)
10: 0.0625°C/LSB, 13-bit word (12 bits plus Sign)
11: 0.03125°C/LSB, 14-bit word (13 bits plus Sign)
4 reserved Always returns zero when read. Recommend customer write zero only.
3 ALERT Pin Status Value is 0 when ALERT output pin is low. Value is 1 when ALERT output pin is high. The ALERT
output pin is reset under any of the following conditions: (1) Cleared by writing a 1 to the ALERT
Reset bit in the configuration register, (2) Measured temperature falls below the TLOW limit, or (3)
cleared via the ARA sequence. Recommend customer write zero only.
www.national.com 14
LM73
Bits Name Description
2 Temperature High
Flag
Bit is set to 1 when the measured temperature exceeds the THIGH limit stored in the programmable
THIGH register. Flag is reset to 0 when both of the following conditions are met: (1) measured
temperature no longer exceeds the programmed THIGH limit and (2) upon reading the Control/Status
register. If the temperature is not longer above the THIGH limit, this status bit remains set until it is
read by the master so that the system can check the history of what caused the ALERT output to go
active. This bit is not cleared after every read if the measured temperature is still above the THIGH
limit.
1 Temperature Low
Flag
Bit is set to 1 when the measured temperature falls below the TLOW limit stored in the programmable
TLOW register. Flag is reset to 0 when both of the following conditions are met: (1) measured
temperature is no longer below the programmed TLOW limit and (2) upon reading the Control/Status
register. If the temperature is no longer below the TLOW limit, the status bit remains set until it is read
by the master so that the system can check the history of what cause the ALERT output to go active.
This bit is not cleared after every read if temperature is still below TLOW limit.
0 Data Available Flag This bit is 0 when the LM73 is in the process of converting a new temperature. It is 1 when the
conversion is done. After initiating a temperature conversion while operating in the one-shot mode,
this status bit can be monitored to indicate when the conversion is done. After triggering the one-shot
conversion, the data in the temperature register is invalid until this bit is high (that is, after completion
of the conversion). On power-up, the LM73 is in continuous conversion mode; while in continuous
conversion mode (the default mode after power-on reset) this bit will always be high. Recommend
customer write zero only.
2.7 IDENTIFICATION REGISTER
Pointer Address 07h (Read Only)
Reset State: 0190h
D15 D14 D13 D12 D11 D10 D9 D8
00000001
D7 D6 D5 D4 D3 D2 D1 D0
10010000
Bits Name Description
15:8 Manufacturer
Identification Byte
Always returns 01h to uniquely identify the manufacturer as National Semiconductor Corporation.
7:4 Product Identification
Nibble
Always returns 9h to uniquely identify this part as the LM73 Temperature Sensor.
3:0 Die Revision Step
Nibble
Always returns 0h to uniquely identify the revision as level zero.
15 www.national.com
LM73
3.0 Application Hints
3.1 THERMAL PATH CONSIDERATIONS
To get the expected results when measuring temperature with
an integrated circuit temperature sensor like the LM73, it is
important to understand that the sensor measures its own die
temperature. For the LM73, the best thermal path between
the die and the outside world is through the LM73's pins. In
the SOT23 package, all the pins on the LM73 will have an
equal effect on the die temperature. Because the pins repre-
sent a good thermal path to the LM73 die, the LM73 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
LM73 die. If the ambient air temperature is significantly dif-
ferent from the printed circuit board temperature, it will have
a small effect on the measured temperature.
3.2 OUTPUT CONSIDERATIONS: TIGHT ACCURACY,
RESOLUTION AND LOW NOISE
The LM73 is well suited for applications that require tight tem-
perature measurement accuracy. In many applications, the
low temperature error can mean better system performance
and, by eliminating a system calibration step, lower produc-
tion cost.
With digital resolution as fine as 0.03125 °C/LSB, the LM73
senses and reports very small changes in its temperature,
making it ideal for applications where temperature sensitivity
is important. For example, the LM73 enables the system to
quickly identify the direction of temperature change, allowing
the processor to take compensating action before the system
reaches a critical temperature.
The LM73 has very low output noise, typically 0.015°C rms,
which makes it ideal for applications where stable thermal
compensation is a priority. For example, in a temperature-
compensated oscillator application, the very small deviation
in successive temperature readings translates to a stable fre-
quency output from the oscillator.
3.3 POWER SUPPLY RAMP-UP CONSIDERATIONS
In systems where there is a large amount of capacitance on
the VDD node, the LM73 power supply ramp-up time can be-
come excessively long. Slow power-supply ramp times may
result in abnormal temperature readings. A linear power-on-
ramp of less than 0.7V/msec and an exponential ramp with
an RC time constant of more than 1.25 msec is categorized
as a slow power-supply ramp. To avoid errors, use the power
up sequence described below.
The software reset sequence is as follows:
1. Allow VDD to reach the specified minimum operating volt-
age, as specified in the Operating Ratings section.
2. Write a “1” to the Full Power Down bit, Bit 7 of the Config-
uration Register, and hold it high for the specified maximum
conversion time for the initial default of 11-bits resolution. This
ensures that a complete reset operation has occurred. See
the Temperature Conversion Time specifications within the
Temperature-to-Digital Characteristics section for more de-
tails.
3. Write a “0” to the Full Power Down bit to restore the LM73
to normal mode.
www.national.com 16
LM73
Physical Dimensions inches (millimeters) unless otherwise noted
6-Lead Thin-SOT23,
Order Number LM73CIMK or LM73CIMKX
NS Package Number MK06A
17 www.national.com
LM73
Notes
LM73 2.7V, SOT-23, 11-to-14 Bit Digital Temperature Sensor with 2-Wire Interface
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