FEATURES
D±1°C REMOTE DIODE SENSOR
D±3°C LOCAL TEMPERATURE SENSOR
DSERIES RESISTANCE CANCELLATION
DTHERM FLAG OUTPUT
DALERT/THERM2 FLAG OUTPUT
DPROGRAMMABLE OVER/UNDER
TEMPERATURE LIMITS
DPROGRAMMABLE RESOLUTION: 9- to 12-Bit
DDIODE FAULT DETECTION
DSMBus SERIAL INTERFACE
APPLICATIONS
DLCD/DLPE/LCOS PROJECTORS
DSERVERS
DINDUSTRIAL CONTROLLERS
DCENTRAL OFFICE TELECOM EQUIPMENT
DDESKTOP AND NOTEBOOK COMPUTERS
DSTORAGE AREA NETWORKS
DESCRIPTION
The TMP401 is a remote temperature sensor monitor with
a built-in local temperature sensor. The remote
temperature sensor diode-connected transistors are
typically low-cost, NPN- or PNP-type transistors or diodes
that are an integral part of microcontrollers,
microprocessors, or FPGAs.
Remote accuracy 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.
Device ID Register
Manufacturer ID Register
THERM Hysteresis Register
Consecutive Alert
Configuration Register
TR
TL
Status Register
Conversion Rate
Register
One− Shot
Start Register
D+
1
5
7
8
2
3
Bus Interface
TMP401
Resolution Register
Pointer Register
Configuration Register
Local Temp Low Limit
Local THERM Limit
Local Temp High Limit
Remote Temp Low Limit
Remote THERM Limit
Remote Temp High Limit
Remote
Te mpe ratur e
Register
Local
Temperature
Register
Temperature
Comparators
Interrupt
Configuration
SCL
GND
THERM
4
6ALERT/THERM2
V+
V+
SDA
D−
TMP401
SBOS371A − AUGUST 2006 − REVISED OCT OBER 2007
+15C Programmable, Remote/Local, Digital Out
TEMPERATURE SENSOR
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Copyright 2006-2007, Texas Instruments Incorporated
Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of Texas Instruments
semiconductor products and disclaimers thereto appears at the end of this data sheet.
DLP is a trademark of Texas Instruments. All other trademarks are the property of their respective owners.
! !
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2
ABSOLUTE MAXIMUM RATINGS(1)
Power Supply, VS7.0V. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Input Voltage(2) −0.5V to VS + 0.5V. . . . . . . . . . . . . . . . . . . . . . . . . .
Input Current 10mA. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Operating Temperature Range −55 °C to +127°C. . . . . . . . . . . . . . .
Storage Temperature Range −60 °C to +130°C. . . . . . . . . . . . . . . . .
Junction Temperature (TJ max) +150°C. . . . . . . . . . . . . . . . . . . . . .
ESD Rating:
Human Body Model (HBM) 4000V. . . . . . . . . . . . . . . . . . . . . . .
Charged Device Model (CDM) 1000V. . . . . . . . . . . . . . . . . . . .
(1) Stresses above these ratings may cause permanent damage.
Exposure to absolute maximum conditions for extended periods
may degrade device reliability. These are stress ratings only, and
functional operation of the device at these or any other conditions
beyond those specified is not supported.
(2) Input voltage rating applies to all TMP401 input voltages.
This integrated circuit can be damaged by ESD. Texas
Instruments recommends that all integrated circuits be
handled with appropriate precautions. Failure to observe
proper handling and installation procedures can cause damage.
ESD damage can range from subtle performance degradation to
complete device failure. Precision integrated circuits may be more
susceptible to damage because very small parametric changes could
cause the device not to meet its published specifications.
PACKAGE/ORDERING INFORMATION(1)
PRODUCT DESCRIPTION ADDRESS PACKAGE-LEAD PACKAGE
DESIGNATOR PACKAGE
MARKING
TMP401 Remote Junction Temperature Sensor 1001100 MSOP-8 DGK BRB
(1) For the most current package and ordering information, see the Package Option Addendum at the end of this document, or see the TI website
at www.ti.com.
PIN CONFIGURATION
TOP VIEW MSOP-8
1
2
3
4
8
7
6
5
SCL
SDA
ALERT/THERM2
GND
V+
D+
D−
THERM
TMP401
PIN ASSIGNMENTS
PIN NAME DESCRIPTION
1 V+ Positive supply (3V to 5.5V)
2 D+ Positive connection to remote
temperature sensor
3 D− Negative connection to remote
temperature sensor
4 THERM Thermal flag, active low, open-drain;
requires pull-up resistor to V+
5 GND Ground
6 ALERT/THERM2 Alert (reconfigurable as second
thermal flag), active low, open-drain;
requires pull-up resistor to V+
7 SDA Serial data line for SMBus, open-drain;
requires pull-up resistor to V+
8 SCL Serial clock line for SMBus,
open-drain; requires pull-up resistor to
V+
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ELECTRICAL CHARACTERISTICS: VS = 3V to 5.5V
At TA = −40°C to +125°C, and VS = 3V to 5.5V, unless otherwise noted.
TMP401
PARAMETER CONDITION MIN TYP MAX UNITS
TEMPERATURE ERROR
Local Temperature Sensor TELOCAL TA = −40°C to +125°C±1±3°C
Remote Temperature Sensor(1) TEREMOTE TA = +15°C to +75°C, TD = −40°C to +150°C, VS = 3.3V ±1°C
TA = −40°C to +100°C, TD = −40°C to +150°C, VS = 3.3V ±3°C
TA = −40°C to +125°C, TD = −40°C to +150°C±5°C
vs Supply
Local/Remote VS = 3V to 5.5V ±0.2 ±0.5 °C/V
TEMPERATURE MEASUREMENT
Conversion Time (per channel) One Shot Mode 115 ms
Resolution
Local Temperature Sensor (programmable) 9 12 Bits
Remote Temperature Sensor 12 Bits
Remote Sensor Source Currents
High Series Resistance 3kΩ Max 120 µA
Medium High 60 µA
Medium Low 12 µA
Low 6 µA
Remote T ransistor Ideality Factor ηTMP401 Optimized Ideality Factor 1.008
SMBus INTERFACE
Logic Input High Voltage (SCL, SDA) VIH 2.1 V
Logic Input Low Voltage (SCL, SDA) VIL 0.8 V
Hysteresis 500 mV
SMBus Output Low Sink Current 6 mA
Logic Input Current −1 +1 µA
SMBus Input Capacitance (SCL, SDA) 3 pF
SMBus Clock Frequency 3.4 MHz
SMBus T imeout 30 35 ms
SCL Falling Edge to SDA Valid Time 1µs
DIGITAL OUTPUTS
Output Low Voltage VOL IOUT = 6mA 0.15 0.4 V
High-Level Output Leakage Current IOH VOUT = VS0.1 1 µA
ALERT/THERM2 Output Low Sink Current ALERT/THERM2 Forced to 0.4V 6 mA
THERM Output Low Sink Current THERM Forced to 0.4V 6 mA
POWER SUPPLY
Specified Voltage Range VS3 5.5 V
Quiescent Current IQ0.0625 Conversions per Second 25 30 µA
8 Conversions per Second 350 425 µA
Serial Bus Inactive, Shutdown Mode 3 10 µA
Serial Bus Active, fS = 400kHz, Shutdown Mode 90 µA
Serial Bus Active, fS = 3.4MHz, Shutdown Mode 350 µA
Power-On Reset Threshold POR 1.6 2.5 V
TEMPERATURE RANGE
Specified Range −40 +125 °C
Storage Range −60 +130 °C
Thermal Resistance qJA
MSOP-8 150 °C/W
(1) Tested with less than 5Ω effective series resistance and 100pF dif ferential input capacitance.
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TYPICAL CHARACTERISTICS
At TA = +25°C and VS = 5.0V, unless otherwise noted.
Figure 1
3
2
1
0
−1
−2
−3
REMOTE TEMPERATURE ERROR
vs TEMPERATURE
Ambient Temperature, TA(_C)
−50 −25 1251007550250
Remote Temperature Error (_C)
VS=3.3V
TREMOTE =+25
_C
30 Typical Units Shown
η= 1.008
Figure 2
3
2
1
0
−1
−2
−3
LOCAL TEMPERATURE ERROR
vs TEMPERATURE
Ambient Temperature, TA(_C)
−50 −25 1251007550250
Local Temperature Error (_C)
28 Typical Units Shown
VS=3.3V
60
40
20
0
−20
−40
−60
REMOTE TEMPERATURE ERROR
vs LEAKAGE RESISTANCE
Leakage Resistance (MΩ
)
0 5 10 15 20 25 30
Remote Temperature Error (_C)
R−GND
R−V
S
Figure 3 Figure 4
16
14
12
10
8
6
4
2
0
−2
REMOTE TEMPERATURE ERROR vs SERIES RESISTANCE
(Diode−Connected Configuration; see Figure 11)
RS(Ω)
0 500 1000 1500 2000 2500 3000
Remote Temperature Error (_C)
VS=5.5V
VS=3.3V
Figure 5
REMOTE TEMPERATURE ERROR vs SERIES RESISTANCE
(Transistor−Connected Configuration; see Figure 11)
RS(Ω
)
0 500 1000 1500 2000 2500 3000
VS=5.5V
VS=3.3V
5
4
3
2
1
0
−1
Remote Temperature Error (_C)
3
2
1
0
−1
−2
−3
REMOTE TEMPERATURE ERROR
vs DIFFERENTIAL CAPACITANCE
Capacitance (nF)
0 0.5 1.0 1.5 2.0 2.5 3.0
Remote Temperature Error (_C)
Figure 6
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TYPICAL CHARACTERISTICS (continued)
At TA = +25°C and VS = 5.0V, unless otherwise noted.
Figure 7
25
20
15
10
5
0
−5
−10
−15
−20
−25
TEMPERATURE ERROR
vs POWER−SUPPLY NOISE FREQUENCY
Frequency (MHz)
0 5 10 15
Temperature Error (_C)
Local 100mVPP Noise
Remote 100mVPP Noise
Local 250mVPP Noise
Remote 250mVPP Noise
Figure 8
500
450
400
350
300
250
200
150
100
50
0
QUIESCENT CURRENT
vs CONVERSION RATE
Conversion Rate (samples/s)
0.0625 0.125 0.25 0.5 1 2 4 8
IQ(µA)
VS=5.5V
VS=3.3V
Figure 9
500
450
400
350
300
250
200
150
100
50
0
SHUTDOWN QUIESCENT CURRENT
vs SCL CLOCK FREQUENCY
SCL CLock Frequency (Hz)
1k 10k 100k 1M 10M
IQ(µA)
VS=3.3V
VS=5.5V
Figure 10
8
7
6
5
4
3
2
1
0
SHUTDOWN QUIESCENT CURRENT
vs SUPPLY VOLTAGE
VS(V)
3.0 3.5 4.0 4.5 5.0 5.5
IQ(µA)
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APPLICATIONS INFORMATION
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 MSOP-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/under temperature 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 0.1µF power-supply bypass capacitor
is recommended for good local bypassing. Figure 11
shows a typical configuration for the TMP401.
0.1µF10kΩ
(typ)
10kΩ
(typ)
10kΩ
(typ)
10kΩ
(typ)
TMP401
D+
D−
V+
1
8
7
6
4
5
3
2
RS(2)
RS(2) CDIFF(3)
CDIFF(3)
RS(2)
RS(2)
GND
SCL
SDA
ALERT/THERM2
THERM
+5V
SMBus
Controller
Fan Controller
Diode−connected configuration(1):
Series Resistance
Transistor−connected configuration(1):
(1) Diode−connected configuration provides better settling time.
Transistor−connected configuration provides better series resistance
cancellation. 2N3906 PNP.
(2) RSshould be < 1.5kΩin most applications.
(3) CDIFF should be < 1000pF in most applications.
NOTES:
Figure 11. Basic Connections
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SERIES RESISTANCE CANCELLATION
Series resistance in an application circuit that typically
results from printed circuit board (PCB) trace resistance
and remote line length (see Figure 11) is automatically
cancelled by the TMP401, preventing what would
otherwise result in a temperature offset. When using a 5V
supply voltage, a total of up to 3kΩ of series line resistance
is cancelled by the TMP401, eliminating the need for
additional characterization and temperature offset
correction. Series line resistance should be limited to
500Ω total when using a 3.3V supply voltage. See typical
characteristics curves (Figure 4 and Figure 5) for details
on the effect of series resistance and power-supply
voltage on sensed remote temperature error.
DIFFERENTIAL INPUT CAPACITANCE
The TMP401 tolerates differential input capacitance of up
to 1000pF with minimal change in temperature error. The
effect of capacitance on sensed remote temperature error
is shown in Figure 6, Remote Temperature Error vs
Differential Capacitance.
TEMPERATURE MEASUREMENT DATA
Temperature measurement data is taken over a default
range o f 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 is represented in binary form,
as shown in Table 1, 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,
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 observed.
Table 1. Temperature Data Format
(Local and Remote Temperature High Bytes)
LOCAL/REMOTE TEMPERATURE REGISTER
HIGH BYTE VALUE (+15C RESOLUTION)
TEMP
STANDARD BINARY EXTENDED BINARY
TEMP
(5C) BINARY HEX BINARY HEX
−64 0000 0000 00 0000 0000 00
−50 0000 0000 00 0000 1110 0E
−25 0000 0000 00 0010 0111 27
00000 0000 00 0100 0000 40
10000 0001 01 0100 0001 41
50000 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
75 0100 1011 4B 1000 1011 8B
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; it 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.
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Table 2. Decimal Fraction Temperature Data Format (Local and Remote Temperature Low Bytes)
REMOTE
TEMPERATURE
REGISTER
LOW BYTE VALUE
LOCAL
TEMPERATURE
REGISTER
LOW BYTE VALUE
0.06255C RESOLUTION 0.55C RESOLUTION 0.255C RESOLUTION 0.1255C RESOLUTION 0.06255C RESOLUTION
TEMP
(5C)
STANDARD
AND
EXTENDED
BINARY HEX
STANDARD
AND
EXTENDED
BINARY HEX
STANDARD
AND
EXTENDED
BINARY HEX
STANDARD
AND
EXTENDED
BINARY HEX
STANDARD
AND
EXTENDED
BINARY HEX
0.0000 0000 0000 00 0000 0000 00 0000 0000 00 0000 0000 00 0000 0000 00
0.0625 0001 0000 10 0000 0000 00 0000 0000 00 0000 0000 00 0001 0000 10
0.1250 0010 0000 20 0000 0000 00 0000 0000 00 0010 0000 20 0010 0000 20
0.1875 0011 0000 30 0000 0000 00 0000 0000 00 0010 0000 20 0011 0000 30
0.2500 0100 0000 40 0000 0000 00 0100 0000 40 0100 0000 40 0100 0000 40
0.3125 0101 0000 50 0000 0000 00 0100 0000 40 0100 0000 40 0101 0000 50
0.3750 0110 0000 60 0000 0000 00 0100 0000 40 0110 0000 60 0110 0000 60
0.4375 0111 0000 70 0000 0000 00 0100 0000 40 01 10 0000 60 0111 0000 70
0.5000 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 1 110 0000 E0 1110 0000 E0
0.9375 1111 0000 F0 1000 0000 80 1100 0000 C0 1110 0000 E0 1111 0000 F0
REGISTER INFORMATION
The TMP401 contains multiple registers for holding
configuration information, temperature measurement
results, temperature comparator limits, and status
information. These registers are described in Figure 12
and Table 3.
POINTER REGISTER
Figure 12 shows 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 should 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).
Hysteresis Register
Resolution Register
Configuration Register
Status Register
Consecutive Alert Register
One−ShotRegister
Identification Registers
Conversion Rate Register
Local and Remote Limit Registers
Local and Remote Temperature Registers
SDA
SCL
Pointer Register
I/O
Control
Interface
Figure 12. Internal Register Structure
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Table 3. Register Map
POINTER
ADDRESS
(HEX)
POWER
-
ON
RESET
BIT DESCRIPTION
READ WRITE
RESET
(HEX) D7 D6 D5 D4 D3 D2 D1 D0 REGISTER DESCRIPTION
00 NA 00 LT11 LT10 LT9 LT8 LT7 LT6 LT5 LT4 Local Temperature
(High Byte)
01 NA 00 RT11 RT10 RT9 RT8 RT7 RT6 RT5 RT4 Remote Temperature
(High Byte)
02 NA XX BUSY LHIGH LLOW RHIGH RLOW OPEN RTHRM LTHRM Status Register
03 09 00 MASK1 SD AL/TH 0 0 RANGE 0 0 Configuration Register
04 0A 08 0 0 0 0 R3 R2 R1 R0 Conversion Rate Register
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 0000 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 0000 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)
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 80 TO_EN 0 0 0 C2 C1 C0 0 Consecutive Alert Register
FE NA 55 0 1 0 1 0 1 0 1 Manufacturer ID
FF NA 11 00010001 Device ID
NOTE:NA = Not applicable; register is write-only or read-only.
X = Indeterminate state.
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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 th e t e m perature 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 A DC
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 should be read first. The low byte
register should be read in the next read command. The low
byte register may be left unread if the LSBs are not
needed. Alternatively, the temperature registers may be
read as a 16-bit register by using a single two-byte read
command from address 00h for the local channel result o r
from address 01h for the remote channel result. The high
byte will be output first, followed by the low byte. Both bytes
of this read operation will be from the same ADC
conversion. The power-on reset value of both temperature
registers is 00h.
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/00h (+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/00h (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/00h (+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/00h (0°C in
standard temperature mode; −64°C in extended mode).
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.
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11
STATUS REGISTER
The TMP401 has a status register to report the state of the
temperature comparators. Table 4 shows the Status
Register bits. The Status Register is read-only and is read
by reading from pointer address 02h.
The BUSY bit reads as ‘1’ if the ADC is making a
conversion. It reads as ‘0’ if the ADC is not converting.
The OPEN bit reads as ‘1’ if the remote transistor was
detected a s open since the last read of the Status Register .
The OPEN status is only detected when the ADC is
attempting to convert a remote temperature.
The RTHRM bit reads as ‘1’ if the remote temperature has
exceeded the remote THERM limit and remains greater
than the remote THERM limit less the value in the shared
hysteresis register; see Figure 17.
The LTHRM bit reads as ‘1’ if the local temperature has
exceeded the local THERM limit and remains greater than
the local THERM limit less the value in the shared
hysteresis register; see Figure 17.
The LHIGH and RHIGH bit values depend on the state of
the AL/TH bit in the Configuration Register . If the AL/TH bit
is ‘0’, the LHIGH bit reads as ‘1’ if the local high limit was
exceeded since the last clearing of the Status Register.
The RHIGH bit reads as ‘1’ if the remote high limit was
exceeded since the last clearing of the Status Register. If
the AL/TH bit is ‘1’, the remote high limit and the local high
limit are used to implement a THERM2 function. LHIGH
reads as ‘1’ if the local temperature has exceeded the local
high limit and remains greater than the local high limit less
the value in the Hysteresis Register.
The RHIGH bit reads as ‘1’ if the remote temperature has
exceeded the remote high limit and remains greater than
the remote high limit less the value in the Hysteresis
Register.
The LLOW and RLOW bits are not affected by the AL/TH
bit. The LLOW bit reads as ‘1’ if the local low limit was
exceeded since the last clearing of the Status Register.
The RLOW bit reads as ‘1’ if the remote low limit was
exceeded since the last clearing of the Status Register.
The values of the LLOW, RLOW, and OPEN (as well as
LHIGH and RHIGH when AL/TH is ‘0’) are latched and will
read a s ‘1’ until the Status Register is read or a device reset
occurs. These bits are cleared by reading the Status
Register, provided that the condition causing the flag to be
set no longer exists. The values of BUSY, LTHRM, and
RTHRM (as well as LHIGH and RHIGH when AL/TH is ‘1’)
are not latched and are not cleared by reading the Status
Register. They always indicate the current state, and are
updated appropriately at the end of the corresponding
ADC conversion. Clearing the Status Register bits does
not clear the state of the ALERT pin; an SMBus alert
response address command must be used to clear the
ALERT pin.
The TMP401 NORs LHIGH, LLOW, RHIGH, RLOW, and
OPEN, so a status change for any of these flags from ‘0’
to ‘1’ automatically causes the ALERT pin to go low (only
applies when the ALERT/THERM2 pin is configured for
ALERT mode).
Table 4. Status Register Format
STATUS REGISTER (Read = 02h, W rite = NA)
BIT # D7 D6 D5 D4 D3 D2 D1 D0
BIT NAME BUSY LHIGH LLOW RHIGH RLOW OPEN RTHRM LTHRM
POR VALUE 0(1) 0000000
(1) The BUSY bit will change to ‘1’ almost immediately (<< 100µs) following power-up, as the TMP401 begins the first temperature conversion.
It will be high whenever the TMP401 is converting a temperature reading.
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12
CONFIGURATION REGISTER
The Configuration Register sets the temperature range,
controls Shutdown mode, and determines how the
ALERT/THERM2 pin functions. The Configuration
Register is set by writing to pointer address 09h and read
by reading from pointer address 03h.
The MASK bit (bit 7) enables or disables the ALERT pin
output if AL/TH = 0. If AL/TH = 1 then the MASK bit has no
effect. If MASK is set to ‘0’, the ALERT pin goes low when
one of the temperature measurement channels exceeds
its high or low limits for the chosen number of consecutive
conversions. If the MASK bit is set to ‘1’, the TMP401
retains the ALERT pin status, but the ALERT pin will not
go low.
The shutdown (SD) bit (bit 6) enables or disables the
temperature measurement circuitry. I f S D = 0 , the TMP401
converts continuously at the rate set in the Conversion
Rate Register. When SD is set to ‘1’, the TMP401
immediately stops converting and enters a shutdown
mode. When SD is set to ‘0’ again, the TMP401 resumes
continuous conversions. A single conversion can be
started when SD = 1 by writing to the One-Shot Register.
The AL/TH bit (bit 5) controls whether the ALERT pin
functions in ALERT mode or TH ERM2 mode. If AL/TH = 0,
the ALERT p in o perates a s an i nterrupt p in. I n t his m ode, the
ALERT pin goes low after the set number of consecutive
out-of-limit temperature measurements occur.
If AL/TH = 1, the ALERT/THERM2 pin implements a
THERM function (THERM2). In this mode, THERM2
functions similar to the THERM pin except that the local
high limit and remote high limit registers are used for the
thresholds. THERM2 goes low when either RHIGH or
LHIGH is set.
The temperature range is set by configuring bit 2 of the
Configuration Register. Setting this bit low configures the
TMP401 for the standard measurement range (0°C to
+127°C); temperature conversions will be stored in the
standard binary format. Setting bit 2 high configures the
TMP401 for the extended measurement range (−55°C to
+150°C); temperature conversions will be stored in the
extended binary format (see Table 1).
The remaining bits of the Configuration Register are
reserved and must always be set to ‘0’. The power-on reset
value for this register is 00h. Table 5 summarizes the bits
of the Configuration Register.
Table 5. Configuration Register Bit Descriptions
CONFIGURATION REGISTER (Read = 02h, Write = NA)
BIT NAME FUNCTION POWER-ON RESET VALUE
7 MASK 0 = ALERT Enabled
1 = ALERT Masked 0
6 SD 0 = Run
1 = Shut Down 0
5 AL/TH 0 = ALERT Mode
1 = THERM Mode 0
4, 3 Reserved — 0
2Temperature Range 0 = 0°C to +127°C
1 = −55°C to +150°C0
1, 0 Reserved — 0
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RESOLUTION REGISTER
The RES1 and RES0 bits (resolution bits 1 and 0) of the
Resolution Register set the resolution of the local
temperature measurement channel. Remote temperature
measurement channel resolution is not affected.
Changing the local channel resolution also affects the
conversion time and rate of the TMP401. The Resolution
Register is set by writing to pointer address 1Ah and is
read by reading from pointer address 1Ah. Table 6 shows
the resolution bits for the Resolution Register.
Table 6. Resolution Register:
Local Channel Programmable Resolution
RESOLUTION REGISTER (Read = 1Ah, W rite = 1Ah, POR = 1Ch)
RES1 RES0 RESOLUTION CONVERSION TIME
(Typical)
0 0 9 Bits (0.5°C) 12.5ms
0 1 10 Bits (0.25°C) 25ms
1 0 11 Bits (0.125°C) 50ms
1 1 12 Bits (0.0625°C) 100ms
Bits 2 through 4 of the Resolution Register must always be
set to ‘1’. Bits 5 through 7 of the Resolution Register must
always be set to ‘0’. The power-on reset value of this
register is 1Ch.
CONVERSION RATE REGISTER
The Conversion Rate Register controls the rate at which
temperature conversions are performed. This register
adjusts the idle time between conversions but not the
conversion timing itself, thereby allowing the TMP401
power dissipation to be balanced with the temperature
register update rate. Table 7 shows the conversion rate
options and corresponding current consumption.
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 has been set t o
shutdown mode, an initial 200µs is required before a
one-shot command can be given. This wait time only
applies to the 200µs immediately following shutdown.
One-shot commands can be issued without delay
thereafter.
Table 7. Conversion Rate Register
CONVERSION RATE REGISTER
AVERAGE IQ (typ)
(µA)
R7 R6 R5 R4 R3 R2 R1 R0 CONVERSION/SEC VS = 3V VS = 5V
0 0 0 0 0 0 0 0 0.0625 8 29
0 0 0 0 0 0 0 1 0.125 11 31
0 0 0 0 0 0 1 0 0.25 15 36
0 0 0 0 0 0 1 1 0.5 24 45
0 0 0 0 0 1 0 0 1 41 63
0 0 0 0 0 1 0 1 2 69 92
00000110 4 111 136
07h to 0Fh 8 320 355
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CONSECUTIVE ALERT REGISTER
The value in the Consecutive Alert Register (address 22h)
determines how many consecutive out-of-limit
measurements must occur on a measurement channel
before the ALERT signal is activated. The value in this
register does not affect bits in the Status Register. Values
of one, two, three, or four consecutive conversions can be
selected; one conversion is the default. This function
allows additional filtering for the ALERT pin. The
consecutive alert bits are shown in Table 8.
Table 8. Consecutive Alert Register
CONSECUTIVE ALERT REGISTER
C2 C1 C0 NUMBER OF CONSECUTIVE
OUT-OF-LIMIT MEASUREMENTS
0 0 0 1
0 0 1 2
0 1 1 3
1 1 1 4
NOTE: Bit 7 of the Consecutive Alert Register controls the
enable/disable of the timeout function. See the Timeout
Function section for a description of this feature.
THERM HYSTERESIS REGISTER
The THERM Hysteresis Register stores the hysteresis
value used for the THERM pin alarm function. This register
must be programmed with a value that is less than the
Local Temperature High Limit Register value, Remote
Temperature High Limit Register value, Local THERM
Limit Register value, or Remote THERM Limit Register
value; otherwise, the respective temperature comparator
will not trip on the measured temperature falling edges.
Allowable hysteresis values are shown in Table 9. The
default hysteresis value is 10°C, whether the device is
operating in the standard or extended mode setting.
Table 9. Allowable THERM Hysteresis Values
THERM HYSTERESIS VALUE
TEMPERATURE
(5C) TH[11:4]
(STANDARD BINARY) (HEX)
00000 0000 00
10000 0001 01
50000 0101 05
10 0000 1010 0A
25 0001 1001 19
50 0011 0010 32
75 0100 1011 4B
100 0110 0100 64
125 0111 1101 7D
127 0111 1111 7F
150 1001 0110 96
175 1010 111 1 AF
200 1100 1000 C8
225 1110 0001 E1
255 1111 1111 FF
Table 10. THERM Hysteresis Register Format
THERM HYSTERESIS REGISTER (Read = 21h, Write = 21h)
BIT # D7 D6 D5 D4 D3 D2 D1 D0
BIT NAME TH11 TH10 TH9 TH8 TH7 TH6 TH5 TH4
POR VALUE 00001010
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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. START 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.
Once all data has been transferred, the master generates
a STOP condition. STOP is indicated by pulling SDA from
low to high, while SCL is high.
SERIAL INTERFACE
The TMP401 operates only as a slave device on either th e
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 spike suppression filters
and Schmitt triggers to minimize the effects o f input spikes
and bus noise. The TMP401 supports the transmission
protocol for fast (1kHz to 400kHz) and high-speed (1kHz
to 3.4MHz) modes. All data bytes are transmitted MSB
first.
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).
READ/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 14).
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 is 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 15 for details of this sequence. If repeated
reads from the same register are desired, it is not
necessary to continually send the Pointer Register bytes,
because the TMP401 retains the Pointer Register value
until it is changed by the next write operation. Note that
register bytes are sent MSB first, followed by the LSB.
TIMING DIAGRAMS
The TMP401 is Two-Wire and SMBus compatible.
Figure 13 to Figure 16 describe the various operations on
the TMP401. Bus definitions are given below. Parameters
for Figure 13 are defined in Table 11.
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 Da t a 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 that has been
transmitted by the slave.
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SCL
SDA
t(LOW) tRtFt(HDSTA)
t(HDSTA) t(HDDAT)
t(BUF)
t(SUDAT)
t(HIGH) t(SUSTA) t(SUSTO)
PS SP
Figure 13. Two-Wire Timing Diagram
Table 11. Timing Diagram Definitions for Figure 13
PARAMETER MIN MAX MIN MAX UNITS
SCL Operating Frequency f(SCL) 0.001 0.4 0.001 3.4 MHz
Bus Free Time Between STOP and START Condition t(BUF) 600 160 ns
Hold time after repeated START condition.
After this period, the first clock is generated. t(HDSTA) 100 100 ns
Repeated START Condition Setup Time t(SUSTA) 100 100 ns
STOP Condition Setup Time t(SUSTO) 100 100 ns
Data Hold Time t(HDDAT) 0 0 ns
Data Setup Time t(SUDAT) 100 10 ns
SCL Clock LOW Period t(LOW) 1300 160 ns
SCL Clock HIGH Period t(HIGH) 600 60 ns
Clock/Data Fall Time tF300 160 ns
Clock/Data Rise Time
for SCL ≤ 100kHz tR
tR300
1000 160 ns
Frame 1 Two−Wire Slave Address Byte Frame 2 Pointer Register Byte
Frame 4 Data Byte 2
1
Start By
Master ACK By
TMP401 ACK By
TMP401
ACK By
TMP401 Stop By
Master
191
1
D7 D6 D5 D4 D3 D2 D1 D0
9
Frame 3 Data Byte 1
ACK By
TMP401
1
D7
SDA
(Continued)
SCL
(Continued)
D6 D5 D4 D3 D2 D1 D0
9
9
SDA
SCL
0 0 1 1 0 0 R/W P7 P6 P5 P4 P3 P2 P1 P0 …
…
Figure 14. Two-Wire Timing Diagram for Write Word Format
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Frame 1 Two−Wire Slave Address Byte Frame 2 Pointer Register Byte
1
Start By
Master ACK By
TMP401 ACK By
TMP401
Frame3Two−WireSlaveAddressByte Frame4DataByte1ReadRegister
Start By
Master ACK By
TMP401 ACK By
Master
From
TMP401
1919
1919
SDA
SCL
0 0 1 R/W P7 P6 P5 P4 P3 P2 P1 P0 …
…
…
…
SDA
(Continued)
SCL
(Continued)
SDA
(Continued)
SCL
(Continued)
1001
100
100
R/W D7 D6 D5 D4 D3 D2 D1 D0
Frame5DataByte2ReadRegister
Stop By
Master
ACK By
Master
From
TMP401
19
D7 D6 D5 D4 D3 D2 D1 D0
Figure 15. Two-Wire Timing Diagram for Read Word Format
Frame 1 SMBus ALERT Response Address Byte Frame 2 Slave Address Byte
Start By
Master ACK By
TMP401 From
TMP401 NACK By
Master Stop By
Master
1919
SDA
SCL
ALERT
0001100R/W 1001100
Status
Figure 16. Timing Diagram for SMBus ALERT
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HIGH-SPEED MODE
In order for the Two-Wire bus to operate at frequencies
above 400kHz, the master device must issue a
High-speed mode (Hs-mode) master code (00001XXX) as
the first byte after a START condition to switch the bus to
high-speed operation. The TMP401 will not acknowledge
this byte, but will switch the input filters on SDA and SCL
and the output filter on SDA to operate in Hs-mode,
allowing transfers at up to 3.4MHz. After the Hs-mode
master code has been issued, the master will transmit a
Two-Wire slave address to initiate a data transfer
operation. The bus will continue 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.
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 30ms (typ) between a START and STOP condition. If
the TMP401 is holding the bus low , it releases the bus and
waits for a START condition. To avoid activating the
timeout function, it is necessary to maintain a
communication speed of at least 1kHz for the SCL
operating frequency. The default state of the timeout
function is enabled (bit 7 = high).
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/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 shown in
Table 9. 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), it
functions the same as THERM, but uses the temperatures
stored in the Local/Remote Temperature High/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/Remote Temperature High/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. ALER T also asserts low if the
remote temperature sensor is open-circuit. When the
MASK function is e nabled (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 has been reset.
Measured
Temperature
THERM Limit and ALERT High Limit
ALERT Low Limit and THERM Limit Hysteresis
THERM
ALERT
SMBus ALERT
Read Read
Time Read
Figure 17. SMBus Alert Timing Diagram
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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 may 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
(00011001) on the bus. If the ALERT pin of the TMP401 is
active, the devices will 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 will be high if the temperature is greater
than or equal to one of the temperature high limit settings;
this bit will be low if the temperature is less than one of the
temperature low limit settings. See Figure 16 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 will
clear 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.
SHUTDOWN MODE (SD)
The TMP401 Shutdown Mode allows the user to save
maximum power by shutting down all device circuitry other
than the serial interface, reducing current consumption to
typically less than 3µA; 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 once the current conversion
is completed. When SD is low, the device maintains a
continuous conversion state.
SENSOR FAULT
The TMP401 will sense 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+) − 0.6V (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.
GENERAL CALL RESET
The TMP401 suppo rt s r ese t v i a t he 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.
IDENTIFICATION REGISTERS
The TMP401 allows for the Two-Wire bus controller to
query the device for manufacturer and device IDs to allow
for software identification of the device at the particular
Two-Wire bus address. The manufacturer ID is obtained
by reading from pointer address FEh. The device ID is
obtained by reading from pointer address FFh. The
TMP401 returns 55h for the manufacturer code and 11h for
the device ID. These registers are read-only.
FILTERING
Remote junction temperature sensors are usually
implemented in a noisy environment. Noise is most often
created by fast digital signals, and it can corrupt
measurements. The TMP401 has a built-in 65kHz filter on
the inputs of D+ and D− to minimize the effects of noise.
However, a bypass capacitor placed differentially across
the inputs of the remote temperature sensor is
recommended to make the application more robust
against unwanted coupled signals. The value of the
capacitor should be between 100pF and 1nF. Some
applications attain better overall accuracy with additional
series resistance; however, this is setup-specific. When
series resistance is added, the value should not be greater
than 100Ω.
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REMOTE SENSING
The TMP401 is designed to be used with either discrete
transistors or substrate transistors built into processor
chips and 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, Basic
Connections).
Errors in remote temperature sensor readings will be 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 6µA for ILOW and 120µA 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 the equation to be used
correctly, actual temperature (°C) must be converted to
Kelvin (°K).
TERR +ƪǒh*1.008Ǔ
1.008 ƫ ƪ273.15 )T(°C)ƫ
Where:
η = Ideality factor of remote temperature sensor.
T(°C) = actual temperature.
TERR = Error in TMP401 reading due to η ≠ 1.008.
Degree delta is the same for °C and °K.
For η = 1.004 and T(°C) = 100°C:
TERR +ƪ(1.004*1.008)
1.008 ƫ ƪ273.15)100°Cƫ
TERR +*1.48°C
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 > 0.25V at 6µA, at the highest
sensed temperature.
2. Base-emitter voltage < 0.95V at 120µA, at the
lowest sensed temperature.
3. Base resistance < 100Ω.
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).
MEASUREMENT ACCURACY AND THERMAL
CONSIDERATIONS
The temperature measurement accuracy of the TMP401
depends on the remote and/or local temperature sensor
being at the same temperature as the system point being
monitored. Clearly, if the temperature sensor is not in good
thermal contact with the part of the system being
monitored, then there will be a delay in the response of the
sensor to a temperature change in the system. For remote
temperature sensing applications using a substrate
transistor (or a small, SOT23 transistor) placed close to the
device being monitored, this delay is usually not a concern.
The local temperature sensor inside the TMP401 monitors
the ambient air around the device. The thermal time
constant for the TMP401 is approximately two seconds.
This constant implies that if the ambient air changes
quickly by 100°C, it would take the TMP401 about 10
seconds (that is, five thermal time constants) to settle to
within 1°C of the final value. In most applications, the
TMP401 package is in electrical and therefore thermal
contact with the PCB, as well as subjected to forced
airflow. The accuracy of the measured temperature
directly depends on how accurately the PCB and forced
airflow temperatures represent the temperature that the
TMP401 is measuring. Additionally, the internal power
dissipation of the TMP401 can cause the temperature to
rise above the ambient or PCB temperature. The internal
power dissipated as a result of exciting the remote
temperature sensor is negligible because of the small
currents used. For a 5.5V supply and maximum
conversion rate of eight conversions per second, the
TMP401 dissipates 1.82mW (PDIQ = 5.5V x 330µA). If both
the ALERT/THERM2 and THERM pins are each sinking
1mA, an additional power of 0.8mW is dissipated
(PDOUT = 1mA ×0.4V + 1mA ×0.4V = 0.8mW). Total power
dissipation is then 2.62mW (PDIQ + PDOUT) and, with an
qJA of 150°C/W, causes the junction temperature to rise
approximately 0.393°C above the ambient.
(1)
(2)
"#$%
SBOS371A − AUGUST 2006 − REVISED OCT OBER 2007
www.ti.com
21
LAYOUT CONSIDERATIONS
Remote temperature sensing on the TMP401 measures
very small voltages using very small currents; therefore,
noise at the IC inputs must be minimized. Most
applications using the TMP401 will have high digital
content, with several clocks and logic level transitions
creating a noisy environment. Layout should adhere to the
following guidelines:
1. Place the TMP401 as close to the remote junction
sensor as possible.
2. Route the D+ and D− traces next to each other and
shield them from adjacent signals through the use
of ground guard traces, as shown in Figure 18. If a
multilayer PCB is used, bury these traces between
ground or VDD planes to shield them from extrinsic
noise sources. 5 mil PCB traces are recommended.
3. Minimize additional thermocouple junctions caused
by copper-to-solder connections. If these junctions
are used, make the same number and approximate
locations of copper-to-solder connections in both
the D+ and D− connections to cancel any
thermocouple effects.
4. Use a 0.1µF local bypass capacitor directly
between the V+ and GND of the TMP401, as shown
in Figure 19. Minimize filter capacitance between
D+ and D− to 1000pF or less for optimum
measurement performance. This capacitance
includes any cable capacitance between the
remote temperature sensor and TMP401.
5. If the connection between the remote temperature
sensor and the TMP401 is between 8 inches and 12
feet, use a twisted-wire pair connection. Beyond
this distance (up to 100ft), use a twisted, shielded
pair with the shield grounded as close to the
TMP401 as possible. Leave the remote sensor
connection end of the shield wire open to avoid
ground loops and 60Hz pickup.
GND(1)
D+(1)
D−(1)
GND(1)
NOTE: (1) 5 mil traces with 5 mil spacing.
Ground or V+ layer
on bottom and/or
top, if possible.
Figure 18. Example Signal Traces
1
2
3
4
8
7
6
5
TMP401
0.1µF Capacitor
PCB Via PCB Via
V+ GND
Figure 19. Suggested Bypass Capacitor
Placement
PACKAGE OPTION ADDENDUM
www.ti.com 16-Aug-2012
Addendum-Page 1
PACKAGING INFORMATION
Orderable Device Status (1) Package Type Package
Drawing Pins Package Qty Eco Plan (2) Lead/
Ball Finish MSL Peak Temp (3) Samples
(Requires Login)
TMP401AIDGKR ACTIVE VSSOP DGK 8 2500 Green (RoHS
& no Sb/Br) CU NIPDAU Level-2-260C-1 YEAR
TMP401AIDGKRG4 ACTIVE VSSOP DGK 8 2500 Green (RoHS
& no Sb/Br) CU NIPDAU Level-2-260C-1 YEAR
TMP401AIDGKT ACTIVE VSSOP DGK 8 250 Green (RoHS
& no Sb/Br) CU NIPDAU Level-2-260C-1 YEAR
TMP401AIDGKTG4 ACTIVE VSSOP DGK 8 250 Green (RoHS
& no Sb/Br) CU NIPDAU Level-2-260C-1 YEAR
(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) Eco Plan - The planned eco-friendly classification: Pb-Free (RoHS), Pb-Free (RoHS Exempt), or Green (RoHS & no Sb/Br) - please check http://www.ti.com/productcontent for the latest availability
information and additional product content details.
TBD: The Pb-Free/Green conversion plan has not been defined.
Pb-Free (RoHS): TI's terms "Lead-Free" or "Pb-Free" mean semiconductor products that are compatible with the current RoHS requirements for all 6 substances, including the requirement that
lead not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, TI Pb-Free products are suitable for use in specified lead-free processes.
Pb-Free (RoHS Exempt): This component has a RoHS exemption for either 1) lead-based flip-chip solder bumps used between the die and package, or 2) lead-based die adhesive used between
the die and leadframe. The component is otherwise considered Pb-Free (RoHS compatible) as defined above.
Green (RoHS & no Sb/Br): TI defines "Green" to mean Pb-Free (RoHS compatible), and free of Bromine (Br) and Antimony (Sb) based flame retardants (Br or Sb do not exceed 0.1% by weight
in homogeneous material)
(3) MSL, Peak Temp. -- The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder temperature.
Important Information and Disclaimer:The information provided on this page represents TI's knowledge and belief as of the date that it is provided. TI bases its knowledge and belief on information
provided by third parties, and makes no representation or warranty as to the accuracy of such information. Efforts are underway to better integrate information from third parties. TI has taken and
continues to take reasonable steps to provide representative and accurate information but may not have conducted destructive testing or chemical analysis on incoming materials and chemicals.
TI and TI suppliers consider certain information to be proprietary, and thus CAS numbers and other limited information may not be available for release.
In no event shall TI's liability arising out of such information exceed the total purchase price of the TI part(s) at issue in this document sold by TI to Customer on an annual basis.
TAPE AND REEL INFORMATION
*All dimensions are nominal
Device Package
Type Package
Drawing Pins SPQ Reel
Diameter
(mm)
Reel
Width
W1 (mm)
A0
(mm) B0
(mm) K0
(mm) P1
(mm) W
(mm) Pin1
Quadrant
TMP401AIDGKR VSSOP DGK 8 2500 330.0 12.4 5.3 3.3 1.3 8.0 12.0 Q1
TMP401AIDGKT VSSOP DGK 8 250 180.0 12.4 5.3 3.3 1.3 8.0 12.0 Q1
PACKAGE MATERIALS INFORMATION
www.ti.com 16-Aug-2012
Pack Materials-Page 1
*All dimensions are nominal
Device Package Type Package Drawing Pins SPQ Length (mm) Width (mm) Height (mm)
TMP401AIDGKR VSSOP DGK 8 2500 370.0 355.0 55.0
TMP401AIDGKT VSSOP DGK 8 250 370.0 355.0 55.0
PACKAGE MATERIALS INFORMATION
www.ti.com 16-Aug-2012
Pack Materials-Page 2
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