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TMP401
SBOS371B – AUGUST 2006 – REVISED OCTOBER 2014
TMP401 ±1°C Programmable, Remote and Local, Digital Out Temperature Sensor
1 Features
3 Description
•
•
•
•
•
•
The TMP401 is a remote temperature sensor monitor
with a built-in local temperature sensor. The remote
sensor is capable of monitoring the temperature of
any external PN junction. Typical sense elements
include low-cost NPN- or PNP-type transistors and
diodes, or accessible thermal diodes integrated within
microcontrollers,
microprocessors,
or
fieldprogrammable gate arrays (FPGAs).
1
•
•
•
±1°C Remote Diode Sensor
±3°C Local Temperature Sensor
Series Resistance Cancellation
THERM Flag Output
ALERT/THERM2 Flag Output
Programmable Over- and Undertemperature
Limits
Programmable Resolution: 9- to 12-Bit
Diode Fault Detection
SMBus-Compatible
2 Applications
•
•
•
•
The accuracy of the remote sensor is ±1°C for
multiple IC manufacturers, with no calibration needed.
The two-wire serial interface accepts SMBus write
byte, read byte, send byte, and receive byte
commands to program alarm thresholds and to read
temperature data.
Features included in the TMP401 are series
resistance cancellation, wide remote temperature
measurement range (up to +150°C), diode fault
detection, and temperature alert functions.
Servers and Workstations
Desktop and Notebook Computers
Telecom and Network Infrastructure
Set Top Boxes
Device Information(1)
PART NUMBER
TMP401
PACKAGE
BODY SIZE (NOM)
VSSOP (8)
3.00 mm × 3.00 mm
(1) For all available packages, see the orderable addendum at
the end of the datasheet.
space
space
4
V+
1
V+
5
GND
6
TMP401
Interrupt
Configuration
THERM
ALERT/THERM2
Consecutive Alert
Configuration Register
Remote Temp High Limit
One-Shot
Start Register
Status Register
Remote THERM Limit
Remote Temp Low Limit
Local
Temperature
Register
TL
THERM Hysteresis Register
Local Temp High Limit
Local THERM Limit
Temperature
Comparators
Conversion Rate
Register
Manufacturer ID Register
D+ 2
3
Remote
Temperature
Register
TR
Device ID Register
Configuration Register
DSCL
SDA
Local Temp Low Limit
Resolution Register
8
7
Bus Interface
Pointer Register
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.
TMP401
SBOS371B – AUGUST 2006 – REVISED OCTOBER 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
4
5
6.1
6.2
6.3
6.4
6.5
6.6
6.7
5
5
5
5
6
7
8
Absolute Maximum Ratings ......................................
Handling Ratings.......................................................
Recommended Operating Conditions.......................
Thermal Information ..................................................
Electrical Characteristics: V+ = 3 V to 5.5 V.............
Timing Requirements ................................................
Typical Characteristics ..............................................
Detailed Description ............................................ 10
7.1 Overview ................................................................. 10
7.2 Functional Block Diagram ....................................... 11
7.3
7.4
7.5
7.6
8
Feature Description.................................................
Device Functional Modes........................................
Programming...........................................................
Register Maps .........................................................
12
15
17
20
Application and Implementation ........................ 28
8.1 Application Information............................................ 28
8.2 Typical Application .................................................. 28
9 Power-Supply Recommendations...................... 30
10 Layout................................................................... 31
10.1 Layout Guidelines ................................................. 31
10.2 Layout Examples................................................... 32
11 Device and Documentation Support ................. 34
11.1 Trademarks ........................................................... 34
11.2 Electrostatic Discharge Caution ............................ 34
11.3 Glossary ................................................................ 34
12 Mechanical, Packaging, and Orderable
Information ........................................................... 34
4 Revision History
Changes from Revision A (October 2007) to Revision B
Page
•
Changed format to meet latest data sheet standards ............................................................................................................ 1
•
Added Handling Rating, Recommended Operating Conditions, and Thermal Information tables and Feature
Description, Device Functional Modes, Application and Implementation, Power Supply
Recommendations, Layout, Device and Documentation Support, and Mechanical, Packaging, and Orderable
Information sections................................................................................................................................................................ 1
•
Changed VS to V+ throughout document .............................................................................................................................. 1
•
Changed last Features bullet ................................................................................................................................................. 1
•
Changed Applications section ............................................................................................................................................... 1
•
Changed first paragraph and first sentence of second paragraph in Description section ..................................................... 1
•
Deleted Device Information Table title.................................................................................................................................... 4
•
Changed Input and output voltage parameter name and footnote 2 in Absolute Maximum Ratings table............................ 5
•
Changed Operating temperature range maximum specification in Absolute Maximum Ratings table .................................. 5
•
Changed HBM specifications in Handling Ratings table ....................................................................................................... 5
•
................................................................................................................................................................................................ 5
•
Changed test conditions for TEREMOTE parameter in Electrical Characteristics table ............................................................ 6
•
Changed Temperature Error, TELOCAL and TEREMOTE versus supply parameter name .......................................................... 6
•
Deleted SMBus Interface, SMBus clock frequency and SCL falling edge to SDA valid time parameters from
Electrical Characteristics table .............................................................................................................................................. 6
•
Changed typical and maximum specifications in first two rows of Power Supply, IQ parameter in Electrical
Characteristics table ............................................................................................................................................................... 6
•
Changed test conditions for third row of Power Supply, IQ parameter in Electrical Characteristics table.............................. 6
•
Added Power Supply, UVLO parameter to Electrical Characteristics table .......................................................................... 6
•
Changed Power Supply, POR parameter maximum specification in Electrical Characteristics table ................................... 6
•
Changed Timing Requirements table ..................................................................................................................................... 7
•
Changed title of Standard and Extended Temperature Measurement Range section ....................................................... 12
•
Changed second sentence of High-Speed Mode section ................................................................................................... 16
•
Changed range for high-speed mode in Serial Interface section ........................................................................................ 17
•
Changed POR value and D0 value in Consecutive alert register row of Table 3 ............................................................... 20
2
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Revision History (continued)
•
Added Figure 19 to the Configuration Register section ...................................................................................................... 24
•
Added Figure 20 to the Resolution Register section ........................................................................................................... 24
•
Added Figure 21 to the Conversion Rate Register section ................................................................................................. 25
•
Changed Table 6 for clarity of bit settings ........................................................................................................................... 25
•
Added Figure 22 to the Consecutive Alert Register section ................................................................................................ 26
•
Changed Filtering section .................................................................................................................................................... 29
•
Changed series line resistance value in second sentence of Series Resistance Cancellation section .............................. 29
•
Changed supply voltage in second sentence of Power-Supply Recommendations section ............................................... 30
•
Changed last sentence of Measurement Accuracy and Thermal Considerations section .................................................. 31
•
Added Figure 30 .................................................................................................................................................................. 33
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SBOS371B – AUGUST 2006 – REVISED OCTOBER 2014
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5 Pin Configuration and Functions
DGK Package
VSSOP-8
(Top View)
V+
1
8
SCL
D+
2
7
SDA
D-
3
6
ALERT/THERM2
THERM
4
5
GND
Pin Functions
PIN
NO.
4
I/O
NAME
DESCRIPTION
1
V+
Analog input
Positive supply (3 V to 5.5 V)
2
D+
Analog input
Positive connection to remote temperature sensor
3
D–
Analog input
Negative connection to remote temperature sensor
4
THERM
Digital output
Thermal flag, active low, open-drain; requires pull-up resistor to V+
5
GND
—
6
ALERT/THERM2
Digital output
7
SDA
Digital I/O
Serial data line for SMBus, open-drain; requires pull-up resistor to V+
8
SCL
Digital I/O
Serial clock line for SMBus, open-drain; requires pull-up resistor to V+
Ground
Alert (reconfigurable as second thermal flag), active low, open-drain; requires pull-up
resistor to V+
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6 Specifications
6.1 Absolute Maximum Ratings (1)
MIN
Power supply, V+
Input and output voltage
(2)
–0.5
(2)
V
V
10
mA
+125
°C
+150
°C
–55
Junction Temperature (TJ max)
(1)
UNIT
7.0
(V+) + (0.5)
Input current
Operating temperature range
MAX
Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. These are stress ratings
only, which do not imply functional operation of the device at these or any other conditions beyond those indicated under Recommended
Operating Conditions. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability.
Input voltage rating applies to all TMP401 input and output pins.
6.2 Handling Ratings
Tstg
V(ESD)
(1)
(2)
MIN
MAX
UNIT
–60
+130
°C
Human body model (HBM), per ANSI/ESDA/JEDEC JS-001, all
pins (1)
–3000
3000
Charged device model (CDM), per JEDEC specification
JESD22-C101, all pins (2)
–1000
1000
Storage temperature range
Electrostatic discharge
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.
6.3 Recommended Operating Conditions
MIN
V+
Positive supply (3 V to 5.5 V)
TA
Ambient temperature
NOM
MAX
UNIT
5
V
25
°C
6.4 Thermal Information
TMP401
THERMAL METRIC (1)
DGK (VSSOP)
UNIT
8 PINS
RθJA
Junction-to-ambient thermal resistance
78.8
RθJC(top)
Junction-to-case (top) thermal resistance
71.6
RθJB
Junction-to-board thermal resistance
68.2
ψJT
Junction-to-top characterization parameter
22.0
ψJB
Junction-to-board characterization parameter
67.6
RθJC(bot)
Junction-to-case (bottom) thermal resistance
N/A
(1)
°C/W
For more information about traditional and new thermal metrics, see the IC Package Thermal Metrics application report, SPRA953.
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6.5 Electrical Characteristics: V+ = 3 V to 5.5 V
At TA = –40°C to +125°C, and V+ = 3 V to 5.5 V, unless otherwise noted.
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
±1
UNIT
TEMPERATURE ERROR
TELOCAL
Local temperature sensor
TEREMOTE
Remote temperature sensor
TA = –40°C to +125°C
(1)
±3
°C
TA = +15°C to +75°C, TREMOTE = –40°C to +150°C,
V+ = 3.3 V
±1
°C
TA = –40°C to +100°C, TREMOTE = –40°C to +150°C,
V+ = 3.3 V
±3
°C
TA = –40°C to +125°C, TREMOTE = –40°C to +150°C
TELOCAL and TEREMOTE versus supply
±5
V+ = 3 V to 5.5 V
±0.2
One-shot mode
115
±0.5
°C
°C/V
TEMPERATURE MEASUREMENT
Conversion time (per channel)
Resolution
TELOCAL
(programmable)
9
TEREMOTE
High
Remote sensor
source currents
Series resistance, 3 kΩ max
12
Bits
12
Bits
120
µA
Medium high
60
µA
Medium low
12
µA
6
µA
Low
η
ms
Remote transistor ideality factor
TMP401 optimized ideality factor
1.008
SMBus INTERFACE
VIH
Logic input high voltage (SCL, SDA)
VIL
Logic input low voltage (SCL, SDA)
2.1
V
0.8
Hysteresis
500
SMBus output low sink current
6
Logic input current
mA
–1
SMBus input capacitance (SCL, SDA)
+1
µA
30
35
ms
0.15
0.4
V
0.1
1
µA
3
SMBus timeout
V
mV
pF
DIGITAL OUTPUTS
VOL
Output low voltage
IOUT = 6 mA
IOH
High-level output leakage current
VOUT = V+
ALERT/THERM2 output low sink current
ALERT/THERM2 forced to 0.4 V
6
mA
THERM output low sink current
THERM forced to 0.4 V
6
mA
POWER SUPPLY
V+
Specified voltage range
3
0.0625 conversions per second
8 conversions per second
IQ
Quiescent current
UVLO
Undervoltage lock out
POR
Power-on reset threshold
Serial bus inactive, shutdown mode
V
29
36
µA
390
450
µA
3
10
µA
Serial bus active, fS = 400 kHz, shutdown mode
90
Serial bus active, fS = 2.5 MHz, shutdown mode
350
2.3
5.5
µA
µA
2.4
2.6
V
1.6
2.3
V
°C
TEMPERATURE RANGE
θJA
(1)
6
Specified range
–40
+125
Storage range
–60
+130
Thermal resistance, VSSOP-8
150
°C
°C/W
Tested with less than 5-Ω effective series resistance and 100-pF differential input capacitance.
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6.6 Timing Requirements
See the Timing Diagrams section for timing diagrams.
FAST MODE
PARAMETER
HIGH-SPEED MODE
MIN
MAX
MIN
MAX
UNIT
0.001
0.4
0.001
2.5
MHz
f(SCL)
SCL operating frequency
t(BUF)
Bus free time between stop and start condition
600
160
ns
t(HDSTA)
Hold time after repeated start condition.
After this period, the first clock is generated.
600
160
ns
t(SUSTA)
Repeated start condition setup time
600
160
ns
t(SUSTO)
Stop condition setup time
600
160
ns
t(HDDAT)
Data hold time
100
80
ns
t(SUDAT)
Data setup time
100
60
ns
t(LOW)
SCL clock low period
1300
260
ns
t(HIGH)
SCL clock high period
600
60
ns
tF
tR
Clock rise and fall time
300
40
ns
Data fall time
300
120
ns
Data rise time for SCL ≤ 100 kHz
300
ns
1000
ns
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6.7 Typical Characteristics
At TA = +25°C and V+ = 5.0 V, unless otherwise noted.
3
V+ = 3.3 V
TREMOTE = +25°C
30 Typical Units Shown
h = 1.008
2
1
Local Temperature Error (°C)
Remote Temperature Error (°C)
3
0
-1
-2
-3
28 Typical Units Shown
V+ = 3.3 V
2
1
0
-1
-2
-3
-50
0
-25
25
50
75
100
125
-50
-25
Ambient Temperature, TA (°C)
Figure 1. Remote Temperature Error vs Temperature
25
50
75
100
125
Figure 2. Local Temperature Error vs Temperature
60
16
40
20
14
Remote Temperature Error (°C)
Remote Temperature Error (°C)
0
Ambient Temperature, TA (°C)
R to GND
0
R to V+
-20
-40
12
10
V+ = 3.3 V
8
6
4
V+ = 5.5 V
2
0
-60
-2
0
5
10
15
20
25
30
0
500
1000
1500
2000
2500
3000
Leakage Resistance (MW)
R S (W )
Figure 3. Remote Temperature Error vs Leakage Resistance
Figure 4. Remote Temperature Error vs Series Resistance
(Diode-Connected Configuration; see Figure 11)
3
Remote Temperature Error (°C)
Remote Temperature Error (°C)
5
4
3
V+ = 3.3 V
2
1
0
2
1
0
-1
-2
V+ = 5.5 V
-3
-1
0
8
500
1000
1500
2000
2500
3000
0
0.5
1
1.5
2
2.5
RS (W)
Capacitance (nF)
Figure 5. Remote Temperature Error vs Series Resistance
(Transistor-Connected Configuration; see Figure 11)
Figure 6. Remote Temperature Error vs
Differential Capacitance
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Typical Characteristics (continued)
At TA = +25°C and V+ = 5.0 V, unless otherwise noted.
25
15
10
5
450
400
350
IQ (mA)
Temperature Error (°C)
500
Local 100-mVPP Noise
Remote 100-mVPP Noise
Local 250-mVPP Noise
Remote 250-mVPP Noise
20
0
300
250
-5
200
-10
150
-15
100
-20
50
5
10
V+ = 3.3 V
0
0.0625
-25
0
V+ = 5.5 V
15
0.125
Figure 7. Temperature Error vs
Power-Supply Noise Frequency
0.5
1
2
4
8
Figure 8. Quiescent Current vs Conversion Rate
500
8
450
7
400
6
350
5
300
250
IQ (mA)
IQ (mA)
0.25
Conversion Rate (samples/s)
Frequency (MHz)
V+ = 5.5 V
200
4
3
150
2
100
1
50
V+ = 3.3 V
0
1k
10k
100k
1M
10M
0
3
3.5
4
4.5
5
5.5
SCL CLock Frequency (Hz)
V+ (V)
Figure 9. Shutdown Quiescent Current vs
SCL Clock Frequency
Figure 10. Shutdown Quiescent Current vs Supply Voltage
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7 Detailed Description
7.1 Overview
The TMP401 is a dual-channel digital temperature sensor that combines a local die temperature measurement
channel and a remote junction temperature measurement channel in a single VSSOP-8 package. The TMP401 is
two-wire- and SMBus interface-compatible and is specified over a temperature range of –40°C to +125°C. The
TMP401 contains multiple registers for holding configuration information, temperature measurement results,
temperature comparator limits, and status information.
User-programmed high and low temperature limits stored in the TMP401 can be used to monitor local and
remote temperatures to trigger an over- and undertemperature alarm (ALERT). Additional thermal limits can be
programmed into the TMP401 and used to trigger another flag (THERM) that can be used to initiate a system
response to rising temperatures.
The TMP401 requires only a transistor connected between D+ and D– for proper remote temperature sensing
operation. The SCL and SDA interface pins require pull-up resistors as part of the communication bus, while
ALERT and THERM are open-drain outputs that also need pull-up resistors. ALERT and THERM may be shared
with other devices if desired for a wired-OR implementation. A 0.1-μF power-supply bypass capacitor is
recommended for good local bypassing. Figure 11 shows a typical configuration for the TMP401.
+5 V
0.1 mF
(1)
Transistor-connected configuration :
1
Series Resistance
RS
RS
V+
(2)
SCL
2
(2)
CDIFF
D+
10 kW
(typ)
10 kW
(typ)
10 kW
(typ)
8
TMP401
(3)
3
10 kW
(typ)
SDA
7
DALERT/THERM2
THERM
SMBus
Controller
6
4
Fan Controller
GND
(1)
5
Diode-connected configuration :
RS
RS
(2)
(2)
CDIFF
(3)
(1) The diode-connected configuration provides better settling time. The transistor-connected configuration provides better series resistance
cancellation. A 2N3906 PNP is used in this configuration.
(2) In most applications, RS is < 1.5 kΩ.
(3) In most applications, CDIFF is < 1000 pF.
Figure 11. Basic Connections
10
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7.2 Functional Block Diagram
4
V+
1
V+
5
GND
6
TMP401
Interrupt
Configuration
THERM
ALERT/THERM2
Consecutive Alert
Configuration Register
Remote Temp High Limit
One-Shot
Start Register
Status Register
Remote THERM Limit
Remote Temp Low Limit
Local
Temperature
Register
TL
THERM Hysteresis Register
Local Temp High Limit
Local THERM Limit
Temperature
Comparators
Conversion Rate
Register
Manufacturer ID Register
D+ 2
3
Remote
Temperature
Register
TR
Device ID Register
Configuration Register
DSCL
SDA
Local Temp Low Limit
Resolution Register
8
7
Bus Interface
Pointer Register
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7.3 Feature Description
7.3.1 Standard and Extended Temperature Measurement Range
Temperature measurement data are taken over a default range of 0°C to +127°C for both local and remote
locations. Measurements from –55°C to +150°C can be made both locally and remotely by reconfiguring the
TMP401 for the extended temperature range. To change the TMP401 configuration from the standard to the
extended temperature range, switch bit 2 (RANGE) of the configuration register from low to high.
Temperature data resulting from conversions within the default measurement range are represented in binary
form, as shown in Table 1 (see the Standard Binary column). Note that any temperature below 0°C results in a
data value of zero (00h). Likewise, temperatures above +127°C result in a value of 127 (7Fh). The device can be
set to measure over an extended temperature range by changing bit 2 of the configuration register from low to
high. The change in measurement range and data format from standard binary to extended binary occurs at the
next temperature conversion. For data captured in the extended temperature range configuration, an offset of 64
(40h) is added to the standard binary value, as shown in Table 1 (see the Extended Binary column). This
configuration allows measurement of temperatures below 0°C. Note that binary values corresponding to
temperatures as low as –64°C, and as high as +191°C are possible; however, most temperature-sensing diodes
only measure with the range of –55°C to +150°C. Additionally, the TMP401 is rated only for ambient
temperatures ranging from –40°C to +125°C. Parameters in the Absolute Maximum Ratings table must be
followed.
Table 1. Temperature Data Format (Local and Remote Temperature High Bytes)
LOCAL, REMOTE TEMPERATURE REGISTER HIGH BYTE VALUE (+1°C Resolution)
TEMPERATURE (°C)
STANDARD BINARY
EXTENDED BINARY
BINARY
HEX
BINARY
–64
0000 0000
00
0000 0000
HEX
00
–50
0000 0000
00
0000 1110
0E
–25
0000 0000
00
0010 0111
27
0
0000 0000
00
0100 0000
40
1
0000 0001
01
0100 0001
41
5
0000 0101
05
0100 0101
45
10
0000 1010
0A
0100 1010
4A
25
0001 1001
19
0101 1001
59
50
0011 0010
32
0111 0010
72
8B
75
0100 1011
4B
1000 1011
100
0110 0100
64
1010 0100
A4
125
0111 1101
7D
1011 1101
BD
127
0111 1111
7F
1011 1111
BF
150
0111 1111
7F
1101 0110
D6
175
0111 1111
7F
1110 1111
EF
191
0111 1111
7F
1111 1111
FF
NOTE
Whenever changing between standard and extended temperature ranges, be aware that
the temperatures stored in the temperature limit registers are NOT automatically
reformatted to correspond to the new temperature range format. These temperature limit
values must be reprogrammed in the appropriate binary or extended binary format.
Both local and remote temperature data use two bytes for data storage. The high byte stores the temperature
with 1°C resolution. The second or low byte stores the decimal fraction value of the temperature and allows a
higher measurement resolution; see Table 2. The measurement resolution for the remote channel is 0.0625°C,
and is not adjustable. The measurement resolution for the local channel is adjustable and can be set for 0.5°C,
0.25°C, 0.125°C, or 0.0625°C by setting the RES1 and RES0 bits of the resolution register; see the Resolution
Register section.
12
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Table 2. Decimal Fraction Temperature Data Format (Local and Remote Temperature Low Bytes)
REMOTE TEMPERATURE
REGISTER LOW BYTE VALUE
TEMPERATURE
(°C)
0.0625°C RESOLUTION
STANDARD
AND EXTENDED
BINARY
0.0000
0.0625
LOCAL TEMPERATURE REGISTER LOW BYTE VALUE
0.5°C RESOLUTION
HEX
STANDARD
AND EXTENDED
BINARY
0000 0000
00
0001 0000
10
0.1250
0010 0000
0.1875
0011 0000
0.2500
0.25°C RESOLUTION
HEX
STANDARD
AND EXTENDED
BINARY
0000 0000
00
0000 0000
00
20
0000 0000
30
0000 0000
0100 0000
40
0.3125
0101 0000
0.3750
0.125°C RESOLUTION
HEX
STANDARD
AND EXTENDED
BINARY
0000 0000
00
0000 0000
00
00
0000 0000
00
0000 0000
0000 0000
00
50
0000 0000
0110 0000
60
0.4375
0111 0000
0.5000
0.0625°C RESOLUTION
HEX
STANDARD
AND EXTENDED
BINARY
HEX
0000 0000
00
0000 0000
00
0000 0000
00
0001 0000
10
00
0010 0000
20
0010 0000
20
00
0010 0000
20
0011 0000
30
0100 0000
40
0100 0000
40
0100 0000
40
00
0100 0000
40
0100 0000
40
0101 0000
50
0000 0000
00
0100 0000
40
0110 0000
60
0110 0000
60
70
0000 0000
00
0100 0000
40
0110 0000
60
0111 0000
70
1000 0000
80
1000 0000
80
1000 0000
80
1000 0000
80
1000 0000
80
0.5625
1001 0000
90
1000 0000
80
1000 0000
80
1000 0000
80
1001 0000
90
0.6250
1010 0000
A0
1000 0000
80
1000 0000
80
1010 0000
A0
1010 0000
A0
0.6875
1011 0000
B0
1000 0000
80
1000 0000
80
1010 0000
A0
1011 0000
B0
0.7500
1100 0000
C0
1000 0000
80
1100 0000
C0
1100 0000
C0
1100 0000
C0
0.8125
1101 0000
D0
1000 0000
80
1100 0000
C0
1100 0000
C0
1101 0000
D0
0.8750
1110 0000
E0
1000 0000
80
1100 0000
C0
1110 0000
E0
1110 0000
E0
0.9375
1111 0000
F0
1000 0000
80
1100 0000
C0
1110 0000
E0
1111 0000
F0
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7.3.2 Remote Sensing
The TMP401 is designed to be used with either discrete transistors or substrate transistors built into processor
chips and application-specific integrated circuits (ASICs). Either NPN or PNP transistors can be used, as long as
the base-emitter junction is used as the remote temperature sense. Either a transistor or diode connection can
also be used (see Figure 11).
Errors in remote temperature sensor readings are the consequence of the ideality factor and current excitation
used by the TMP401 versus the manufacturer’s specified operating current for a given transistor. Some
manufacturers specify a high-level and low-level current for the temperature-sensing substrate transistors. The
TMP401 uses 6 μA for ILOW and 120 μA for IHIGH.
The ideality factor (η) is a measured characteristic of a remote temperature sensor diode as compared to an
ideal diode. The ideality factor for the TMP401 is trimmed to be 1.008. For transistors whose ideality factor does
not match the TMP401, Equation 1 can be used to calculate the temperature error. Note that for Equation 1 to be
used correctly, actual temperature (°C) must be converted to Kelvin (°K).
ª º
T ERR = «
» x ¬ª2.73.15 + T qC ¼º
¬« 1.008 ¼»
where
•
•
•
η = Ideality factor of the remote temperature sensor,
T(°C) = actual temperature, and
TERR = Error in the TMP401 reading resulting from η ≠ 1.008. Degree delta is the same for °C and °K.
(1)
For η = 1.004 and T(°C) = 100°C, use Equation 2:
ª 1.004 - 1.008 º
T ERR = «
» x > 2.73.15 + 100qC@
1.008
¬«
¼»
T ERR = -1.48qC
(2)
If a discrete transistor is used as the remote temperature sensor with the TMP401, the best accuracy can be
achieved by selecting the transistor according to the following criteria:
1. Base-emitter voltage > 0.25 V at 6 μA, at the highest sensed temperature.
2. Base-emitter voltage < 0.95 V at 120 μA, at the lowest sensed temperature.
3. Base resistance < 100 Ω.
4. Tight control of VBE characteristics indicated by small variations in hFE (that is, 50 to 150).
Based on these criteria, two recommended small-signal transistors are the 2N3904 (NPN) or 2N3906 (PNP).
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7.4 Device Functional Modes
7.4.1 SMBus Alert Function
The TMP401 supports the SMBus alert function. When pin 6 is configured as an alert output, the ALERT pin of
the TMP401 can be connected as an SMBus alert signal. When a master detects an alert condition on the
ALERT line, the master sends an SMBus alert command (0001 1001b) on the bus. If the ALERT pin of the
TMP401 is active, the devices acknowledge the SMBus alert command and respond by returning its slave
address on the SDA line. The eighth bit (LSB) of the slave address byte indicates whether the temperature
exceeding one of the temperature high limit settings or falling below one of the temperature low limit settings
caused the alert condition. This bit is high if the temperature is greater than or equal to one of the temperature
high limit settings; this bit is low if the temperature is less than one of the temperature low limit settings. See
Figure 15 for details of this sequence.
If multiple devices on the bus respond to the SMBus alert command, arbitration during the slave address portion
of the SMBus alert command determines which device clears its alert status. If the TMP401 wins the arbitration,
its ALERT pin becomes inactive at the completion of the SMBus alert command. If the TMP401 loses the
arbitration, the ALERT pin remains active.
7.4.2 THERM (Pin 4) and ALERT/THERM2 (Pin 6)
The TMP401 has two pins dedicated to alarm functions, the THERM and ALERT/THERM2 pins. Both pins are
open-drain outputs that each require a pull-up resistor to V+. These pins can be wire-ORed together with other
alarm pins for system monitoring of multiple sensors. The THERM pin provides a thermal interrupt that cannot be
software disabled. The ALERT pin is intended for use as an earlier warning interrupt, and can be software
disabled, or masked. The ALERT/THERM2 pin can also be configured for use as THERM2, a second THERM
pin (configuration register, AL/TH bit = 1). The default setting configures pin 6 to function as ALERT (AL/TH = 0).
The THERM pin asserts low when either the measured local or remote temperature is outside of the temperature
range programmed in the corresponding local and remote THERM limit register. The THERM temperature limit
range can be programmed with a wider range than that of the limit registers, which allows ALERT to provide an
earlier warning than THERM. The THERM alarm resets automatically when the measured temperature returns to
within the THERM temperature limit range minus the hysteresis value stored in the THERM hysteresis register.
The allowable values of hysteresis are listed in Table 8. The default hysteresis is 10°C. When the
ALERT/THERM2 pin is configured as a second thermal alarm (configuration register, bit 7 = 0, bit 5 = 1), the pin
functions the same as THERM, but uses the temperatures stored in the local and remote temperature high and
low limit registers to set its comparison range.
When ALERT/THERM2 (pin 6) is configured as ALERT (configuration register, bit 7 = 0, bit 5 = 0), the pin
asserts low when either the measured local or remote temperature violates the range limit set by the
corresponding local and remote temperature high and low limit registers. This alert function can be configured to
assert only if the range is violated a specified number of consecutive times (1, 2, 3, or 4). The consecutive
violation limit is set in the consecutive alert register. False alerts that occur as a result of environmental noise can
be prevented by requiring consecutive faults. ALERT also asserts low if the remote temperature sensor is opencircuit. When the MASK function is enabled (configuration register, bit 7 = 1), ALERT is disabled (that is,
masked). ALERT resets when the master reads the device address, as long as the condition that caused the
alert no longer persists, and the status register is reset.
7.4.3 Sensor Fault
The TMP401 senses a fault at the D+ input resulting from incorrect diode connection or an open circuit. The
detection circuitry consists of a voltage comparator that trips when the voltage at D+ exceeds (V+) – 0.6 V
(typical). The comparator output is continuously checked during a conversion. If a fault is detected, the last valid
measured temperature is used for the temperature measurement result, the OPEN bit (status register, bit 2) is
set high, and (if the alert function is enabled) ALERT asserts low.
When not using the remote sensor with the TMP401, the D+ and D– inputs must be connected together to
prevent meaningless fault warnings.
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Device Functional Modes (continued)
7.4.4 High-Speed Mode
In order for the two-wire bus to operate at frequencies above 400 kHz, the master device must issue a highspeed mode (Hs-mode) master code (0000 1xxxb) as the first byte after a start condition to switch the bus to
high-speed operation. The TMP401 does not acknowledge this byte, but switches the input filters on SDA and
SCL and the output filter on SDA to operate in Hs-mode, allowing transfers at up to 2.5 MHz. After the Hs-mode
master code is issued, the master transmits a two-wire slave address to initiate a data transfer operation. The
bus continues to operate in Hs-mode until a stop condition occurs on the bus. Upon receiving the stop condition,
the TMP401 switches the input and output filter back to fast-mode operation.
7.4.5 Shutdown Mode (SD)
The TMP401 shutdown mode (SD) allows the user to save maximum power by shutting down all device circuitry
other than the serial interface, thus reducing current consumption to typically less than 3 μA; see Figure 10
(Shutdown Quiescent Current vs Supply Voltage). Shutdown mode is enabled when the SD bit of the
configuration register is high; the device shuts down when the current conversion is completed. When SD is low,
the device maintains a continuous conversion state.
7.4.6 One-Shot Conversion
When the TMP401 is in shutdown mode (SD = 1 in the configuration register), a single conversion on both
channels is started by writing any value to the one-shot start register, pointer address 0Fh. This write operation
starts one conversion; the TMP401 returns to shutdown mode when that conversion completes. The value of the
data sent in the write command is irrelevant and is not stored by the TMP401. When the TMP401 is set to
shutdown mode, an initial 200 μs is required before a one-shot command can be given. This wait time only
applies to the 200 μs immediately following shutdown. One-shot commands can be issued without delay
thereafter.
7.4.7 General-Call Reset
The TMP401 supports reset via the two-wire general-call address 00h (0000 0000b). The TMP401 acknowledges
the general-call address and responds to the second byte. If the second byte is 06h (0000 0110b), the TMP401
executes a software reset. This software reset restores the power-on reset state to all TMP401 registers, aborts
any conversion in progress, and clears the ALERT and THERM pins. The TMP401 takes no action in response
to other values in the second byte.
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7.5 Programming
7.5.1 Bus Overview
The TMP401 is SMBus interface-compatible. In SMBus protocol, the device that initiates the transfer is called a
master, and the devices controlled by the master are slaves. The bus must be controlled by a master device that
generates the serial clock (SCL), controls the bus access, and generates the start and stop conditions.
To address a specific device, a start condition is initiated. A start condition is indicated by pulling the data line
(SDA) from a high to low logic level while SCL is high. All slaves on the bus shift in the slave address byte, with
the last bit indicating whether a read or write operation is intended. During the ninth clock pulse, the slave being
addressed responds to the master by generating an acknowledge and pulling SDA low.
Data transfer is then initiated and sent over eight clock pulses followed by an acknowledge bit. During data
transfer SDA must remain stable while SCL is high, because any change in SDA while SCL is high is interpreted
as a control signal.
When all data are transferred, the master generates a stop condition. A stop condition is indicated by pulling
SDA from low to high while SCL is high.
7.5.2 Serial Interface
The TMP401 operates only as a slave device on either the two-wire bus or the SMBus. Connections to either bus
are made via the open-drain I/O lines, SDA and SCL. The SDA and SCL pins feature integrated spikesuppression filters and Schmitt triggers to minimize the effects of input spikes and bus noise. The TMP401
supports the transmission protocol for fast (1 kHz to 400 kHz) and high-speed (1 kHz to 2.5 MHz) modes. All
data bytes are transmitted MSB first.
7.5.3 Serial Bus Address
To communicate with the TMP401, the master must first address slave devices via a slave address byte. The
slave address byte consists of seven address bits, and a direction bit indicating the intent of executing a read or
write operation. The address of the TMP401 is 4Ch (1001100b).
7.5.4 Read and Write Operations
Accessing a particular register on the TMP401 is accomplished by writing the appropriate value to the pointer
register. The value for the pointer register is the first byte transferred after the slave address byte with the R/W
bit low. Every write operation to the TMP401 requires a value for the pointer register (see Figure 13).
When reading from the TMP401, the last value stored in the pointer register by a write operation is used to
determine which register is read by a read operation. To change the register pointer for a read operation, a new
value must be written to the pointer register. This transaction is accomplished by issuing a slave address byte
with the R/W bit low, followed by the pointer register byte. No additional data are required. The master can then
generate a start condition and send the slave address byte with the R/W bit high to initiate the read command.
See Figure 14 for details of this sequence. If repeated reads from the same register are desired, continually
sending the pointer register bytes is not necessary, because the TMP401 retains the pointer register value until
changed by the next write operation. Note that register bytes are sent MSB first, followed by the LSB.
7.5.5 Timeout Function
When bit 7 of the consecutive alert register is set high, the TMP401 timeout function is enabled. The TMP401
resets the serial interface if either SCL or SDA are held low for 30 ms (typ) between a start and stop condition. If
the TMP401 is holding the bus low, the device releases the bus and waits for a start condition. To avoid
activating the timeout function, a communication speed of at least 1 kHz must be maintained for the SCL
operating frequency. The default state of the timeout function is enabled (bit 7 = high).
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Programming (continued)
7.5.6 Timing Diagrams
The TMP401 is two-wire and SMBus compatible. Figure 12 to Figure 15 describe the various operations on the
TMP401. Parameters for Figure 12 are defined in Timing Requirements table. Bus definitions are as follows:
Bus Idle: Both SDA and SCL lines remain high.
Start Data Transfer: A change in the state of the SDA line from high to low while the SCL line is high,
defines a start condition. Each data transfer is initiated with a start condition.
Stop Data Transfer: A change in the state of the SDA line from low to high while the SCL line is high
defines a stop condition. Each data transfer terminates with a repeated start or stop condition.
Data Transfer: The number of data bytes transferred between a start and a stop condition is not limited and
is determined by the master device. The receiver acknowledges the transfer of data.
Acknowledge: Each receiving device, when addressed, is obliged to generate an acknowledge bit. A device
that acknowledges must pull down the SDA line during the acknowledge clock pulse in such a way that the
SDA line is stable low during the high period of the acknowledge clock pulse. Setup and hold times must be
taken into account. On a master receive, data transfer termination can be signaled by the master generating
a not-acknowledge on the last byte transmitted by the slave.
t(LOW)
tF
tR
t(HDSTA)
SCL
t(HDSTA)
t(HIGH)
t(SUSTO)
t(SUSTA)
t(HDDAT)
t(SUDAT)
SDA
t(BUF)
P
S
S
P
Figure 12. Two-Wire Timing Diagram
1
9
9
1
SCL
¼
1
SDA
0
0
1
1
0
0
R/W
Start By
Master
P7
P6
P5
P4
P3
P2
P1
P0
ACK By
Device
ACK By
Device
Frame 2 Pointer Register Byte
Frame 1 Two-Wire Slave Address Byte
9
1
¼
1
9
SCL
(Continued)
SDA
(Continued)
D7
D6
D5
D4
D3
D2
D1
D0
D7
D6
D5
D4
D3
D2
D1
D0
ACK By
Device
ACK By
Device
Stop By
Master
Frame 4 Data Byte 2
Frame 3 Data Byte 1
Figure 13. Two-Wire Timing Diagram for Write Word Format
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Programming (continued)
1
9
1
9
SCL
¼
SDA
1
0
0
1
1
0
R/W
0
P7
Start By
Master
P6
P5
P4
P3
P2
P1
P0
¼
ACK By
Device
ACK By
Device
Frame 1 Two-Wire Slave Address Byte
Frame 2 Pointer Register Byte
1
9
1
9
SCL
(Continued)
¼
SDA
(Continued)
1
0
0
1
1
0
0
D7
R/W
Start By
Master
D6
D5
D4
D3
D2
ACK By
Device
D0
¼
From
Device
Frame 3 Two-Wire Slave Address Byte
1
D1
ACK By
Master
Frame 4 Data Byte 1 Read Register
9
SCL
(Continued)
SDA
(Continued)
D7
D6
D5
D4
D3
D2
D1
D0
From
Device
ACK By
Master
Stop By
Master
Frame 5 Data Byte 2 Read Register
Figure 14. Two-Wire Timing Diagram for Read Word Format
ALERT
1
9
1
9
SCL
SDA
0
0
0
1
1
Start By
Master
0
0
R/W
1
0
0
1
1
0
ACK By
Device
Frame 1 SMBus ALERT Response Address Byte
0
From
Device
Status
NACK By
Master
Stop By
Master
Frame 2 Slave Address Byte
Figure 15. Timing Diagram for SMBus Alert
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7.6 Register Maps
The TMP401 contains multiple registers for holding configuration information, temperature measurement results,
temperature comparator limits, and status information. These registers are described in Figure 16 and Table 3.
Pointer Register
Local and Remote Temperature Registers
Local and Remote Limit Registers
Hysteresis Register
SDA
Status Register
I/O
Control
Interface
Configuration Register
Resolution Register
SCL
Conversion Rate Register
One-Shot Register
Consecutive Alert Register
Identification Registers
Figure 16. Internal Register Structure
Table 3. Register Map
POINTER
ADDRESS (HEX)
READ
WRITE
POWERON
RESET
(HEX)
00
NA
00
01
NA
00
RT11
RT10
RT9
RT8
RT7
RT6
RT5
RT4
02
NA
XX
BUSY
LHIGH
LLOW
RHIGH
RLOW
OPEN
RTHRM
LTHRM
03
09
00
MASK1
SD
AL/TH
0
0
RANGE
0
0
04
0A
08
0
0
0
0
R3
R2
R1
R0
05
0B
55
LTH11
LTH10
LTH9
LTH8
LTH7
LTH6
LTH5
LTH4
Local temperature high limit
(high byte)
06
0C
00
LTL11
LTL10
LTL9
LTL8
LTL7
LTL6
LTL5
LTL4
Local temperature low limit
(high byte)
07
0D
55
RTH11
RTH10
RTH9
RTH8
RTH7
RTH6
RTH5
RTH4
Remote temperature high limit
(high byte)
08
0E
00
RTL11
RTL10
RTL9
RTL8
RTL7
RTL6
RTL5
RTL4
Remote temperature low limit
(high byte)
NA
0F
XX
X
X
X
X
X
X
X
X
One-shot start
10
NA
00
RT3
RT2
RT1
RT0
0
0
0
0
Remote temperature (low byte)
13
13
00
RTH3
RTH2
RTH1
RTH0
0
0
0
0
Remote temperature high limit
(low byte)
14
14
00
RTL3
RTL2
RTL1
RTL0
0
0
0
0
Remote temperature low limit
(low byte)
15
NA
00
LT3
LT2
LT1
LT0
0
0
0
0
Local temperature (low byte)
16
16
00
LTH3
LTH2
LTH1
LTH0
0
0
0
0
Local temperature high limit
(low byte)
17
17
00
LTL3
LTL2
LTL1
LTL0
0
0
0
0
Local temperature low limit
(low byte)
20
BIT DESCRIPTION
D7
D6
D5
D4
D3
D2
D1
D0
REGISTER DESCRIPTION
LT11
LT10
LT9
LT8
LT7
LT6
LT5
LT4
Local temperature (high byte)
Remote temperature (high byte)
Status register
Configuration register
Conversion rate register
19
19
55
RTHL11
RTHL10
RTHL9
RTHL8
RTHL7
RTHL6
RTHL5
RTHL4
Remote THERM limit
1A
1A
1C
0
0
0
1
1
1
RES1
RES0
Resolution register
20
20
55
LTHL11
LTHL10
LTHL9
LTHL8
LTHL7
LTHL6
LTHL5
LTHL4
Local THERM limit
21
21
0A
TH11
TH10
TH9
TH8
TH7
TH6
TH5
TH4
THERM hysteresis
22
22
81
TO_EN
0
0
0
C2
C1
C0
1
Consecutive alert register
FE
NA
55
0
1
0
1
0
1
0
1
Manufacturer ID
FF
NA
11
0
0
0
1
0
0
0
1
Device ID
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7.6.1 Pointer Register
Figure 16 illustrates the internal register structure of the TMP401. The 8-bit pointer register is used to address a
given data register. The pointer register identifies which of the data registers respond to a read or write command
on the two-wire bus. This register is set with every write command. A write command must be issued to set the
proper value in the pointer register before executing a read command. Table 3 describes the pointer address of
the registers available in the TMP401. The power-on reset (POR) value of the pointer register is 00h (0000
0000b).
7.6.2 Temperature Registers
The TMP401 has four 8-bit registers that hold temperature measurement results. Both the local channel and the
remote channel have a high byte register that contains the most significant bits (MSBs) of the temperature ADC
result and a low byte register that contains the least significant bits (LSBs) of the temperature ADC result. The
local channel high byte address is 00h; the local channel low byte address is 15h. The remote channel high byte
is at address 01h; the remote channel low byte address is 10h. These registers are read-only and are updated by
the ADC each time a temperature measurement is completed.
The TMP401 contains circuitry to assure that a low byte register read command returns data from the same ADC
conversion as the immediately preceding high byte read command. This assurance remains valid only until
another register is read. For proper operation, the high byte of a temperature register must be read first. Read
the low byte register in the next read command. The low byte register may be left unread if the LSBs are not
needed. Alternatively, the temperature registers can be read as a 16-bit register by using a single two-byte read
command from address 00h for the local channel result or from address 01h for the remote channel result. The
high byte is output first, followed by the low byte. Both bytes of this read operation are from the same ADC
conversion. The power-on reset value of both temperature registers is 00h.
7.6.3 Limit Registers
The TMP401 has 11 registers for setting comparator limits for both the local and remote measurement channels.
These registers have read and write capability. The high and low limit registers for both channels span two
registers, as do the temperature registers. The local temperature high limit is set by writing the high byte to
pointer address 0Bh and writing the low byte to pointer address 16h, or by using a single two-byte write
command (high byte first) to pointer address 0Bh. The local temperature high limit is obtained by reading the
high byte from pointer address 05h and the low byte from pointer address 16h, or by using a two-byte read
command from pointer address 05h. The power-on reset value of the local temperature high limit is 55h,
standard, and 00h, extended (+85°C in standard temperature mode; +21°C in extended temperature mode).
Similarly, the local temperature low limit is set by writing the high byte to pointer address 0Ch and writing the low
byte to pointer address 17h, or by using a single two-byte write command to pointer address 0Ch. The local
temperature low limit is read by reading the high byte from pointer address 06h and the low byte from pointer
address 17h, or by using a two-byte read from pointer address 06h. The power-on reset value of the local
temperature low limit register is 00h, standard and extended (0°C in standard temperature mode; –64°C in
extended mode).
The remote temperature high limit is set by writing the high byte to pointer address 0Dh and writing the low byte
to pointer address 13h, or by using a two-byte write command to pointer address 0Dh. The remote temperature
high limit is obtained by reading the high byte from pointer address 07h and the low byte from pointer address
13h, or by using a two-byte read command from pointer address 07h. The power-on reset value of the remote
temperature high limit register is 55h, standard, and 00h, extended (+85°C in standard temperature mode; +21°C
in extended temperature mode).
The remote temperature low limit is set by writing the high byte to pointer address 0Eh and writing the low byte to
pointer address 14h, or by using a two-byte write to pointer address 0Eh. The remote temperature low limit is
read by reading the high byte from pointer address 08h and the low byte from pointer address 14h, or by using a
two-byte read from pointer address 08h. The power-on reset value of the remote temperature low limit register is
00h, standard and extended (0°C in standard temperature mode; –64°C in extended mode).
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The TMP401 also has a THERM limit register for both the local and the remote channels. These registers are
eight bits and allow for THERM limits set to 1°C resolution. The local channel THERM limit is set by writing to
pointer address 20h. The remote channel THERM limit is set by writing to pointer address 19h. The local channel
THERM limit is obtained by reading from pointer address 20h; the remote channel THERM limit is read by
reading from pointer address 19h. The power-on reset value of the THERM limit registers is 55h (+85°C in
standard temperature mode; +21°C in extended temperature mode). The THERM limit comparators also have
hysteresis. The hysteresis of both comparators is set by writing to pointer address 21h. The hysteresis value is
obtained by reading from pointer address 21h. The value in the hysteresis register is an unsigned number
(always positive). The power-on reset value of this register is 0Ah (+10°C).
Whenever changing between standard and extended temperature ranges, be aware that the temperatures stored
in the temperature limit registers are not automatically reformatted to correspond to the new temperature range
format. These values must be reprogrammed in the appropriate binary or extended binary format.
7.6.4 Status Register
The TMP401 has a status register to report the state of the temperature comparators. Figure 17 shows the status
register bits. The status register is read-only and is read by reading from pointer address 02h.
Figure 17. Status Register (Read = 02h, Write = NA, POR = XXh)
D7
BUSY (1)
R-0b
D6
LHIGH
R-0b
D5
LLOW
R-0b
D4
RHIGH
R-0b
D3
RLOW
R-0b
D2
OPEN
R-0b
D1
RTHRM
R-0b
D0
LTHRM
R-0b
LEGEND: R = Read only; -n = value after reset
(1)
The BUSY bit will change to ‘1’ almost immediately (
