NSC LM95231 Precision dual remote diode temperature sensor with smbus interface and trutherm technology Datasheet

LM95231
Precision Dual Remote Diode Temperature Sensor with
SMBus Interface and TruTherm™ Technology
General Description
The LM95231 is a precision dual remote diode temperature
sensor (RDTS) that uses National’s TruTherm technology.
The 2-wire serial interface of the LM95231 is compatible with
SMBus 2.0. The LM95231 can sense three temperature
zones, it can measure the temperature of its own die as well
as two diode connected transistors. The LM95231 includes
digital filtering and an advanced input stage that includes
analog filtering and TruTherm technology that reduces
processor-to-processor non-ideality spread. The diode connected transistors can be a “thermal diode” as found in Intel
and AMD processors or can simply be a diode connected
MMBT3904 transistor. TruTherm technology allows accurate
measurement of “thermal diodes” found on small geometry
processes, 90nm and below. The LM95231 supports user
selectable thermal diode non-ideality of either a Pentium ® 4
processor on 90nm process or 2N3904.
The LM95231 resolution format for remote temperature
readings can be programmed to be 11-bits signed or unsigned with the digital filtering disabled. When the filtering is
enabled the resolution increases to 13-bits signed or unsigned. In the unsigned mode the LM95231 remote diode
readings can resolve temperatures above 127˚C. Local temperature readings have a resolution of 9-bits plus sign.
Features
n Accurately senses die temperature of remote ICs or
diode junctions
n Uses TruTherm technology for precision “thermal diode”
temperature measurement
n Thermal diode input stage with analog filtering
n Thermal diode digital filtering
n Intel Pentium 4 processor on 90nm process or 2N3904
non-ideality selection
n Remote diode fault detection
n On-board local temperature sensing
n Remote temperature readings without digital filtering:
— 0.125 ˚C LSb
— 10-bits plus sign or 11-bits programmable resolution
— 11-bits resolves temperatures above 127 ˚C
n Remote temperature readings with digital filtering:
— 0.03125 ˚C LSb with filtering
— 12-bits plus sign or 13-bits programmable resolution
— 13-bits resolves temperatures above 127 ˚C
n Local temperature readings:
— 0.25 ˚C
— 9-bits plus sign
n Status register support
n Programmable conversion rate allows user optimization
of power consumption
n Shutdown mode one-shot conversion control
n SMBus 2.0 compatible interface, supports TIMEOUT
n 8-pin MSOP package
Key Specifications
j Remote Temperature Accuracy
j Local Temperature Accuracy
± 0.75˚C (max)
± 3.0˚C (max)
j Supply Voltage
3.0V to 3.6V
j Supply Current
402µA (typ)
Applications
n Processor/Computer System Thermal Management
(e.g. Laptop, Desktop, Workstations, Server)
n Electronic Test Equipment
n Office Electronics
Connection Diagram
MSOP-8
20120202
TOP VIEW
TruTherm™ is a trademark of National Semiconductor Corporation.
I2C ® is a registered trademark of Philips Corporation.
Pentium ® is a registered trademark of Intel Corporation.
© 2006 National Semiconductor Corporation
DS201202
www.national.com
LM95231 Precision Dual Remote Diode Temperature Sensor with SMBus Interface and TruTherm
Technology
August 2006
LM95231
Ordering Information
Package
Marking
NS Package
Number
Transport
Media
SMBus Device
Address
Thermal Diode
Accuracy
LM95231BIMM
T23B
MUA08A (MSOP-8)
1000 Units on Tape and
Reel
010 1011
± 0.75
LM95231BIMMX
T23B
MUA08A (MSOP-8)
3500 Units on Tape and
Reel
010 1011
± 0.75
LM95231BIMM-1
T25B
MUA08A (MSOP-8)
1000 Units on Tape and
Reel
001 1001
± 0.75
LM95231BIMMX-1
T25B
MUA08A (MSOP-8)
3500 Units on Tape and
Reel
001 1001
± 0.75
LM95231BIMM-2
T26B
MUA08A (MSOP-8)
1000 Units on Tape and
Reel
010 1010
± 0.75
LM95231BIMMX-2
T26B
MUA08A (MSOP-8)
3500 Units on Tape and
Reel
010 1010
± 0.75
LM95231CIMM
T23C
MUA08A (MSOP-8)
1000 Units on Tape and
Reel
010 1011
± 1.25
LM95231CIMMX
T23C
MUA08A (MSOP-8)
3500 Units on Tape and
Reel
010 1011
± 1.25
LM95231CIMM-1
T25C
MUA08A (MSOP-8)
1000 Units on Tape and
Reel
001 1001
± 1.25
LM95231CIMMX-1
T25C
MUA08A (MSOP-8)
3500 Units on Tape and
Reel
001 1001
± 1.25
LM95231CIMM-2
T26C
MUA08A (MSOP-8)
1000 Units on Tape and
Reel
010 1010
± 1.25
LM95231CIMMX-2
T26C
MUA08A (MSOP-8)
3500 Units on Tape and
Reel
010 1010
± 1.25
Part Number
Typical Application
20120203
Pin Descriptions
Label
Pin #
D1+
1
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Function
Typical Connection
Diode Current Source
2
To Diode Anode. Connected to remote discrete
diode-connected transistor junction or to the
diode-connected transistor junction on a remote IC
whose die temperature is being sensed. A capacitor
is not required between D1+ and D1-. A 100 pF
capacitor between D1+ and D1− can be added and
may improve performance in noisy systems.
LM95231
Pin Descriptions
(Continued)
Label
Pin #
Function
Typical Connection
D1−
2
Diode Return Current Sink
To Diode Cathode. A capacitor is not required
between D1+ and D1-. A 100 pF capacitor between
D1+ and D1− can be added and may improve
performance in noisy systems.
D2+
3
Diode Current Source
To Diode Anode. Connected to remote discrete
diode-connected transistor junction or to the
diode-connected transistor junction on a remote IC
whose die temperature is being sensed. A capacitor
is not required between D2+ and D2-. A 100 pF
capacitor between D2+ and D2− can be added and
may improve performance in noisy systems.
D2−
4
Diode Return Current Sink
To Diode Cathode. A capacitor is not required
between D2+ and D2-. A 100 pF capacitor between
D2+ and D2− can be added and may improve
performance in noisy systems.
GND
5
Power Supply Ground
System low noise ground
VDD
6
Positive Supply Voltage
Input
DC Voltage from 3.0 V to 3.6 V. VDD should be
bypassed with a 0.1 µF capacitor in parallel with
100 pF. The 100 pF capacitor should be placed as
close as possible to the power supply pin. Noise
should be kept below 200 mVp-p, a 10 µF capacitor
may be required to achieve this.
SMBDAT
7
SMBus Bi-Directional Data
Line, Open-Drain Output
From and to Controller; may require an external
pull-up resistor
SMBCLK
8
SMBus Clock Input
From Controller; may require an external pull-up
resistor
Simplified Block Diagram
20120201
3
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LM95231
Absolute Maximum Ratings (Note 1)
Supply Voltage
−0.3 V to 6.0 V
Voltage at SMBDAT, SMBCLK
Voltage at Other Pins
Soldering process must comply with National’s reflow
temperature profile specifications. Refer to
http://www.national.com/packaging/. (Note 5)
−0.5V to 6.0V
−0.3 V to (VDD + 0.3 V)
Input Current at All Pins (Note 2)
± 5 mA
Operating Ratings
Package Input Current (Note 2)
30 mA
(Notes 1, 3)
SMBDAT Output Sink Current
10 mA
Operating Temperature Range
0˚C to +125˚C
Junction Tempeature (Note 3)
125˚C
Electrical Characteristics
Temperature Range
TMIN≤TA≤TMAX
Storage Temperature
−65˚C to +150˚C
ESD Susceptibility (Note 4)
Human Body Model
2000 V
Machine Model
LM95231BIMM, LM95231CIMM
0˚C≤TA≤+85˚C
Supply Voltage Range (VDD)
+3.0V to +3.6V
200 V
Temperature-to-Digital Converter Characteristics
Unless otherwise noted, these specifications apply for VDD=+3.0Vdc to 3.6Vdc. Boldface limits apply for TA = TJ =
TMIN≤TA≤TMAX; all other limits TA= TJ=+25˚C, unless otherwise noted. TJ is the junction temperature of the LM95231. TD is the
junction temperature of the remote thermal diode.
Parameter
Conditions
Typical
LM95231
BIMM
LM95231
CIMM
Units
(Note 6)
Limits
(Note 7)
Limits
(Note 7)
(Limit)
±1
±3
±3
Accuracy Using Local Diode
TA = 0˚C to +85˚C, (Note 8)
Accuracy Using Remote Diode, see(Note 9)
for Thermal Diode Processor Type.
TA = +20˚C to
+40˚C; TD =
+45˚C to +85˚C
Intel 90nm
Thermal
Diode
± 0.75
˚C (max)
TA = +20˚C to
+40˚C; TD =
+45˚C to +85˚C
MMBT3904
Thermal
Diode
± 1.25
˚C (max)
TA = +20˚C to
+40˚C; TD =
+45˚C to +85˚C
Intel 90nm
and
MMBT3904
Thermal
Diodes
TA = +0˚C to
+85˚C; TD =
+25˚C to
+140˚C
Intel 90nm
and
MMBT3904
Thermal
Diodes
± 2.5
˚C (max)
± 1.25
˚C (max)
± 2.5
˚C (max)
Remote Diode Measurement Resolution with
filtering turned off
10+sign/11
Bits
0.125
˚C
Remote Diode Measurement Resolution with
digital filtering turned on
12+sign/13
Bits
Local Diode Measurement Resolution
0.03125
˚C
9+sign
Bits
0.25
˚C
Conversion Time of All Temperatures at the
Fastest Setting
(Note 11) TruTherm Mode
Disabled
75.8
83.9
83.9
ms (max)
TruTherm Mode enabled
79.2
87.7
87.7
ms (max)
Average Quiescent Current (Note 10)
SMBus Inactive, 1 Hz
conversion rate
402
545
545
µA (max)
Shutdown
272
µA
D− Source Voltage
0.4
V
Diode Source Current Ratio
16
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4
(Continued)
Unless otherwise noted, these specifications apply for VDD=+3.0Vdc to 3.6Vdc. Boldface limits apply for TA = TJ =
TMIN≤TA≤TMAX; all other limits TA= TJ=+25˚C, unless otherwise noted. TJ is the junction temperature of the LM95231. TD is the
junction temperature of the remote thermal diode.
Parameter
Conditions
Diode Source Current
Power-On Reset Threshold
Typical
LM95231
BIMM
LM95231
CIMM
Units
(Note 6)
Limits
(Note 7)
Limits
(Note 7)
(Limit)
(VD+ − VD−) = + 0.65V;
high-level
176
300
300
µA (max)
100
100
µA (min)
Low-level
11
2.7
1.8
2.7
1.8
V (max)
V (min)
Measure on VDD input, falling
edge
µA
Logic Electrical Characteristics
Digital DC Characteristics
Unless otherwise noted, these specifications apply for VDD=+3.0 to 3.6 Vdc. Boldface limits apply for TA = TJ = TMIN to
TMAX; all other limits TA= TJ=+25˚C, unless otherwise noted.
Symbol
Parameter
Conditions
Typical
Limits
Units
(Note 6)
(Note 7)
(Limit)
SMBDAT, SMBCLK INPUTS
VIN(1)
Logical “1” Input Voltage
2.1
V (min)
VIN(0)
Logical “0”Input Voltage
0.8
V (max)
VIN(HYST)
SMBDAT and SMBCLK Digital Input
Hysteresis
400
IIN(1)
Logical “1” Input Current
VIN = VDD
0.005
IIN(0)
Logical “0” Input Current
VIN = 0 V
−0.005
CIN
Input Capacitance
mV
± 10
± 10
µA (max)
µA (max)
5
pF
SMBDAT OUTPUT
IOH
High Level Output Current
VOH = VDD
10
µA (max)
VOL
SMBus Low Level Output Voltage
IOL = 4mA
IOL = 6mA
0.4
0.6
V (max)
SMBus Digital Switching Characteristics
Unless otherwise noted, these specifications apply for VDD=+3.0 Vdc to +3.6 Vdc, CL (load capacitance) on output lines = 80
pF. Boldface limits apply for TA = TJ = TMIN to TMAX; all other limits TA = TJ = +25˚C, unless otherwise noted. The switching
characteristics of the LM95231 fully meet or exceed the published specifications of the SMBus version 2.0. The following parameters are the timing relationships between SMBCLK and SMBDAT signals related to the LM95231. They adhere to but are
not necessarily the SMBus bus specifications.
Symbol
Parameter
Conditions
fSMB
SMBus Clock Frequency
tLOW
SMBus Clock Low Time
from VIN(0)max to VIN(0)max
Typical
Limits
(Note 6)
(Note 7)
(Limit)
100
10
kHz (max)
kHz (min)
4.7
25
µs (min)
ms (max)
tHIGH
SMBus Clock High Time
from VIN(1)min to VIN(1)min
tR,SMB
SMBus Rise Time
(Note 12)
1
4.0
tF,SMB
SMBus Fall Time
(Note 13)
0.3
tOF
Output Fall Time
CL = 400pF,
IO = 3mA, (Note 13)
Units
µs (min)
µs (max)
µs (max)
250
ns (max)
tTIMEOUT SMBDAT and SMBCLK Time Low for Reset of
Serial Interface (Note 14)
25
35
ms (min)
ms (max)
Data In Setup Time to SMBCLK High
250
ns (min)
tSU;DAT
5
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LM95231
Temperature-to-Digital Converter Characteristics
LM95231
Logic Electrical Characteristics
(Continued)
SMBus Digital Switching Characteristics
(Continued)
Unless otherwise noted, these specifications apply for VDD=+3.0 Vdc to +3.6 Vdc, CL (load capacitance) on output lines = 80
pF. Boldface limits apply for TA = TJ = TMIN to TMAX; all other limits TA = TJ = +25˚C, unless otherwise noted. The switching
characteristics of the LM95231 fully meet or exceed the published specifications of the SMBus version 2.0. The following parameters are the timing relationships between SMBCLK and SMBDAT signals related to the LM95231. They adhere to but are
not necessarily the SMBus bus specifications.
Symbol
Parameter
Conditions
Typical
Limits
Units
(Note 6)
(Note 7)
(Limit)
tHD;DAT
Data Out Stable after SMBCLK Low
300
1075
ns (min)
ns (max)
tHD;STA
Start Condition SMBDAT Low to SMBCLK
Low (Start condition hold before the first clock
falling edge)
100
ns (min)
tSU;STO
Stop Condition SMBCLK High to SMBDAT
Low (Stop Condition Setup)
100
ns (min)
tSU;STA
SMBus Repeated Start-Condition Setup Time,
SMBCLK High to SMBDAT Low
0.6
µs (min)
SMBus Free Time Between Stop and Start
Conditions
1.3
µs (min)
tBUF
SMBus Communication
20120209
Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is
guaranteed to be functional, but do not guarantee specific performance limits. For guaranteed specifications and test conditions, see the Electrical Characteristics.
The guaranteed specifications apply only for the test condition listed. Some performance characteristics may degrade when the device is not operated under the
listed test conditions. Operation of the device beyond the Maximum Operating Ratings is not recommended.
Note 2: When the input voltage (VI) at any pin exceeds the power supplies (VI < GND or VI > VDD), the current at that pin should be limited to 5 mA.
Parasitic components and or ESD protection circuitry are shown in the figures below for the LM95231’s pins. Care should be taken not to forward bias the parasitic
diode, D1, present on pins: D1+, D2+, D1−, D2−. Doing so by more than 50 mV may corrupt the temperature measurements.
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6
Pin
#
Label
Circuit
1
D1+
A
2
D1−
A
3
D2+
A
4
D2−
A
5
GND
B
6
VDD
B
7
SMBDAT
C
8
SMBCLK
C
LM95231
Logic Electrical Characteristics
(Continued)
Pin ESD Protection Structure Circuits
Circuit C
Circuit A
Circuit B
Note 3: Thermal resistance junction-to-ambient when attached to a printed circuit board with 1oz. foil and no airflow:
– MSOP-8 = 210˚C/W
Note 4: Human body model, 100pF discharged through a 1.5kΩ resistor. Machine model, 200pF discharged directly into each pin.
Note 5: Reflow temperature profiles are different for packages containing lead (Pb) than for those that do not.
Note 6: Typicals are at TA = 25˚C and represent most likely parametric norm at time of product characterization. The typical specifications are not guaranteed.
Note 7: Limits are guaranteed to National’s AOQL (Average Outgoing Quality Level).
Note 8: Local temperature accuracy does not include the effects of self-heating. The rise in temperature due to self-heating is the product of the internal power
dissipation of the LM95231 and the thermal resistance. See (Note 3) for the thermal resistance to be used in the self-heating calculation.
Note 9: The accuracy of the LM95231 is guaranteed when using the thermal diode of Pentium 4 processor on 90nm process or an MMBT3904 type transistor, as
selected in the Remote Diode Model Select register.
Note 10: Quiescent current will not increase substantially when the SMBus is active.
Note 11: This specification is provided only to indicate how often temperature data is updated. The LM95231 can be read at any time without regard to conversion
state (and will yield last conversion result).
Note 12: The output rise time is measured from (VIN(0)max + 0.15V) to (VIN(1)min − 0.15V).
Note 13: The output fall time is measured from (VIN(1)min - 0.15V) to (VIN(1)min + 0.15V).
Note 14: Holding the SMBDAT and/or SMBCLK lines Low for a time interval greater than tTIMEOUT will reset the LM95231’s SMBus state machine, therefore setting
SMBDAT and SMBCLK pins to a high impedance state.
7
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LM95231
Typical Performance Characteristics
Thermal Diode Capacitor or PCB Leakage Current Effect
Remote Diode Temperature Reading
Remote Temperature Reading Sensitivity to Thermal
Diode Filter Capacitance
20120205
20120207
Conversion Rate Effect on Average Power Supply
Current
20120247
The 2-wire serial interface, of the LM95231, is compatible
with SMBus 2.0 and I2C ® . Please see the SMBus 2.0 specification for a detailed description of the differences between
the I2C bus and SMBus.
The temperature conversion rate is programmable to allow
the user to optimize the current consumption of the LM95231
to the system requirements. The LM95231 can be placed in
shutdown to minimize power consumption when temperature data is not required. While in shutdown, a 1-shot conversion mode allows system control of the conversion rate
for ultimate flexibility.
The remote diode temperature resolution is variable and
depends on whether the digital filter is activated. When the
digital filter is active the resolution is thirteen bits and is
programmable to 13-bits unsigned or 12-bits plus sign, with
a least-significant-bit (LSb) weight for both resolutions of
0.03125˚C. When the digital filter is inactive the resolution is
eleven bits and is programmable to 11-bits unsigned or
10-bits plus sign, with a least-significant-bit (LSb) weight for
both resolutions of 0.125˚C. The unsigned resolution allows
1.0 Functional Description
The LM95231 is a digital sensor that can sense the temperature of 3 thermal zones using a sigma-delta analog-to-digital
converter. It can measure its local die temperature and the
temperature of two external transistor junctions using a ∆Vbe
temperature sensing method. The LM95231 can support two
external transistor types, a Pentium 4 processor on 90nm
process thermal diode or a 2N3904 diode connected transistor. The transistor type is register programmable and does
not require software intervention after initialization. The
LM95231 has an advanced input stage using National Semiconductor’s TruTherm technology that reduces the spread in
non-ideality found in Pentium 4 processors on 90nm process. Internal analog filtering has been included in the thermal diode input stage thus minimizing the need for external
thermal diode filter capacitors. In addition a digital filter has
been added. These noise immunity improvements in the
analog input stage along with the digital filtering will allow
longer trace tracks or cabling to the thermal diode than
previous thermal diode sensor devices.
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8
LM95231
1.0 Functional Description
(Continued)
the remote diodes to sense temperatures above 127˚C.
Local temperature resolution is not programmable and is
always 9-bits plus sign and has a 0.25˚C LSb.
The LM95231 remote diode temperature accuracy will be
trimmed for the thermal diode of a Pentium 4 processor on
90nm process or a 2N3904 transistor and the accuracy will
be guaranteed only when using either of these diodes when
selected appropriately. TruTherm mode should be enabled
when measuring a Pentium 4 processor on 90nm process
and disabled when measuring a 2N3904 transistor. Enabling
TruTherm mode with a 2N3904 transistor connected may
produce unexpected temperature readings.
Diode fault detection circuitry in the LM95231 can detect the
presence of a remote diode: whether D+ is shorted to VDD,
D- or ground, or whether D+ is floating.
The LM95231 register set has an 8-bit data structure and
includes:
1.
2.
3.
4.
5.
6.
7.
20120247
Most-Significant-Byte (MSB) Local Temperature Register
Least-Significant-Byte (LSB) Local Temperature Register
MSB Remote Temperature 1 Register
LSB Remote Temperature 1 Register
MSB Remote Temperature 2 Register
LSB Remote Temperature 2 Register
Status Register: busy, diode fault
FIGURE 1. Conversion Rate Effect on Power Supply
Current
1.2 POWER-ON-DEFAULT STATES
LM95231 always powers up to these known default states.
The LM95231 remains in these states until after the first
conversion.
1. Command Register set to 00h
2. Local Temperature set to 0˚C until the end of the first
conversion
3. Remote Diode Temperature set to 0˚C until the end of
the first conversion
8.
Configuration Register: resolution control, conversion
rate control, standby control
9. Remote Diode Filter Setting
10. Remote Diode Model Select
4.
5.
Remote Diode digital filters are on.
Remote Diode 1 model is set to Pentium 4 processor on
90nm process with TruTherm mode enabled. Remote
Diode 2 model is set to 2N3904 with TruTherm mode
disabled.
6. Status Register depends on state of thermal diode inputs
11. Remote Diode TruTherm Mode Control
12. 1-shot Register
13. Manufacturer ID
14. Revision ID
1.1 CONVERSION SEQUENCE
7.
In the power up default state the LM95231 takes maximum a
77.5 ms to convert the Local Temperature, Remote Temperature 1 and 2, and to update all of its registers. Only
during the conversion process is the busy bit (D7) in the
Status register (02h) high. These conversions are addressed
in a round robin sequence. The conversion rate may be
modified by the Conversion Rate bits found in the Configuration Register (03h). When the conversion rate is modified a
delay is inserted between conversions, the actual maximum
conversion time remains at 87.7 ms. Different conversion
rates will cause the LM95231 to draw different amounts of
supply current as shown in Figure 1.
Configuration register set to 00h; continuous conversion,
typical time = 85.8 ms when TruTherm Mode is enabled
for Remote 1 only
1.3 SMBus INTERFACE
The LM95231 operates as a slave on the SMBus, so the
SMBCLK line is an input and the SMBDAT line is bidirectional. The LM95231 never drives the SMBCLK line and it
does not support clock stretching. According to SMBus
specifications, the LM95231 has a 7-bit slave address. All
bits A6 through A0 are internally programmed and can not be
changed by software or hardware. The SMBus slave address is dependent on the LM95231 part number ordered:
Part Number
9
A6
A5
A4
A3
A2
LM95231BIMM,
LM95231CIMM
0
1
0
1
0
A1 A0
1
1
LM95231BIMM-1,
LM95231CIMM-1
0
0
1
1
0
0
1
LM95231BIMM-2,
LM95231CIMM-2
0
1
0
1
0
1
0
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LM95231
1.0 Functional Description
13-bit, unsigned binary
(Continued)
Temperature
1.4 TEMPERATURE DATA FORMAT
Temperature data can only be read from the Local and
Remote Temperature registers .
Remote temperature data with the digital filter off is represented by an 11-bit, two’s complement word or unsigned
binary word with an LSb (Least Significant Bit) equal to
0.125˚C. The data format is a left justified 16-bit word available in two 8-bit registers. Unused bits will always report "0".
11-bit, 2’s complement (10-bit plus sign)
Temperature
Digital Output
Binary
Hex
+125˚C
0111 1101 0000 0000
7D00h
+25˚C
0001 1001 0000 0000
1900h
+1˚C
0000 0001 0000 0000
0100h
+0.125˚C
0000 0000 0010 0000
0020h
Digital Output
Binary
Hex
+255.875˚C
1111 1111 1110 0000
FFE0h
+255˚C
1111 1111 0000 0000
FF00h
+201˚C
1100 1001 0000 0000
C900h
+125˚C
0111 1101 0000 0000
7D00h
+25˚C
0001 1001 0000 0000
1900h
0100h
+1˚C
0000 0001 0000 0000
+0.03125˚C
0000 0000 0000 1000
0008h
0˚C
0000 0000 0000 0000
0000h
Local Temperature data is represented by a 10-bit, two’s
complement word with an LSb (Least Significant Bit) equal to
0.25˚C. The data format is a left justified 16-bit word available in two 8-bit registers. Unused bits will always report "0".
Local temperature readings greater than +127.875˚C are
clamped to +127.875˚C, they will not roll-over to negative
temperature readings.
0˚C
0000 0000 0000 0000
0000h
−0.125˚C
1111 1111 1110 0000
FFE0h
−1˚C
1111 1111 0000 0000
FF00h
Binary
Hex
−25˚C
1110 0111 0000 0000
E700h
+125˚C
0111 1101 0000 0000
7D00h
−55˚C
1100 1001 0000 0000
C900h
+25˚C
0001 1001 0000 0000
1900h
0100h
Temperature
11-bit, unsigned binary
Temperature
Digital Output
Digital Output
+1˚C
0000 0001 0000 0000
+0.25˚C
0000 0000 0100 0000
0040h
0˚C
0000 0000 0000 0000
0000h
−0.25˚C
1111 1111 1100 0000
FFC0h
Binary
Hex
+255.875˚C
1111 1111 1110 0000
FFE0h
−1˚C
1111 1111 0000 0000
FF00h
+255˚C
1111 1111 0000 0000
FF00h
−25˚C
1110 0111 0000 0000
E700h
+201˚C
1100 1001 0000 0000
C900h
−55˚C
1100 1001 0000 0000
C900h
+125˚C
0111 1101 0000 0000
7D00h
+25˚C
0001 1001 0000 0000
1900h
+1˚C
0000 0001 0000 0000
0100h
+0.125˚C
0000 0000 0010 0000
0020h
0˚C
0000 0000 0000 0000
0000h
1.5 SMBDAT OPEN-DRAIN OUTPUT
The SMBDAT output is an open-drain output and does not
have internal pull-ups. A “high” level will not be observed on
this pin until pull-up current is provided by some external
source, typically a pull-up resistor. Choice of resistor value
depends on many system factors but, in general, the pull-up
resistor should be as large as possible without effecting the
SMBus desired data rate. This will minimize any internal
temperature reading errors due to internal heating of the
LM95231. The maximum resistance of the pull-up to provide
a 2.1V high level, based on LM95231 specification for High
Level Output Current with the supply voltage at 3.0V, is 82kΩ
(5%) or 88.7kΩ (1%).
Remote temperature data with the digital filter on is represented by a 13-bit, two’s complement word or unsigned
binary word with an LSb (Least Significant Bit) equal to
0.03125˚C (1/32˚C). The data format is a left justified 16-bit
word available in two 8-bit registers. Unused bits will always
report "0".
13-bit, 2’s complement (12-bit plus sign)
Temperature
Binary
Hex
+125˚C
0111 1101 0000 0000
7D00h
+25˚C
0001 1001 0000 0000
1900h
+1˚C
0000 0001 0000 0000
0100h
+0.03125˚C
0000 0000 0000 1000
0008h
0˚C
0000 0000 0000 0000
0000h
−0.03125˚C
1111 1111 1111 1000
FFF8h
−1˚C
1111 1111 0000 0000
FF00h
−25˚C
1110 0111 0000 0000
E700h
−55˚C
1100 1001 0000 0000
C900h
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1.6 DIODE FAULT DETECTION
The LM95231 is equipped with operational circuitry designed
to detect fault conditions concerning the remote diodes. In
the event that the D+ pin is detected as shorted to GND, D−,
VDD or D+ is floating, the Remote Temperature reading is
–128.000 ˚C if signed format is selected and +255.875 if
unsigned format is selected. In addition, the appropriate
status register bits RD1M or RD2M (D1 or D0) are set. When
TruTherm mode is active the condition of diode short of D+
to D− will not be detected. Connecting a 2N3904 transistor
with TruTherm mode active may cause a detection of a diode
fault.
Digital Output
10
Register will point to one of the Read Temperature Registers because that will be the data most frequently read
from the LM95231), then the read can simply consist of
an address byte, followed by retrieving the data byte.
2. If the Command Register needs to be set, then an
address byte, command byte, repeat start, and another
address byte will accomplish a read.
The data byte has the most significant bit first. At the end of
a read, the LM95231 can accept either acknowledge or No
Acknowledge from the Master (No Acknowledge is typically
used as a signal for the slave that the Master has read its
last byte). When retrieving all 11 bits from a previous remote
diode temperature measurement, the master must insure
that all 11 bits are from the same temperature conversion.
This may be achieved by reading the MSB register first. The
LSB will be locked after the MSB is read. The LSB will be
unlocked after being read. If the user reads MSBs consecutively, each time the MSB is read, the LSB associated with
that temperature will be locked in and override the previous
LSB value locked-in.
(Continued)
1.7 COMMUNICATING with the LM95231
The data registers in the LM95231 are selected by the
Command Register. At power-up the Command Register is
set to “00”, the location for the Read Local Temperature
Register. The Command Register latches the last location it
was set to. Each data register in the LM95231 falls into one
of four types of user accessibility:
1. Read only
2.
3.
Write only
Write/Read same address
4. Write/Read different address
A Write to the LM95231 will always include the address byte
and the command byte. A write to any register requires one
data byte.
Reading the LM95231 can take place either of two ways:
1.
If the location latched in the Command Register is correct (most of the time it is expected that the Command
11
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LM95231
1.0 Functional Description
LM95231
1.0 Functional Description
(Continued)
20120211
(a) Serial Bus Write to the Internal Command Register
20120210
(b) Serial Bus Write to the internal Command Register followed by a Data Byte
20120212
(c) Serial Bus byte Read from a Register with the internal Command Register preset to desired value.
20120214
(d) Serial Bus Write followed by a Repeat Start and Immediate Read
FIGURE 2. SMBus Timing Diagrams for Access of Data
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12
2.
(Continued)
1.8 SERIAL INTERFACE RESET
In the event that the SMBus Master is RESET while the
LM95231 is transmitting on the SMBDAT line, the LM95231
must be returned to a known state in the communication
protocol. This may be done in one of two ways:
1.
When SMBDAT is HIGH, have the master initiate an
SMBus start. The LM95231 will respond properly to an
SMBus start condition at any point during the communication. After the start the LM95231 will expect an SMBus
Address address byte.
1.9 ONE-SHOT CONVERSION
The One-Shot register is used to initiate a single conversion
and comparison cycle when the device is in standby mode,
after which the device returns to standby. This is not a data
register and it is the write operation that causes the one-shot
conversion. The data written to this address is irrelevant and
is not stored. A zero will always be read from this register.
When SMBDAT is LOW, the LM95231 SMBus state
machine resets to the SMBus idle state if either SMBDAT or SMBCLK are held low for more than 35ms
(tTIMEOUT). Note that according to SMBus specification
2.0 all devices are to timeout when either the SMBCLK
or SMBDAT lines are held low for 25-35ms. Therefore, to
insure a timeout of all devices on the bus the SMBCLK
or SMBDAT lines must be held low for at least 35ms.
2.0 LM95231 Registers
Command register selects which registers will be read from or written to. Data for this register should be transmitted during the
Command Byte of the SMBus write communication.
P7
P6
P5
P4
P3
P2
P1
P0
Command
P0-P7: Command
Register Summary
Name
Command
(Hex)
Power-On
Default Value
(Hex)
Read/Write
# of used
bits
Comments
Status Register
02h
-
RO
5
4 status bits and 1 busy bit
Configuration Register
03h
00h
R/W
5
Includes conversion rate
control
Remote Diode Filter Control
06h
05h
R/W
2
Controls thermal diode filter
setting
Remote Diode Model Type
Select
30h
01h
R/W
2
Selects the 2N3904 or
Pentium 4 processor on 90nm
process thermal diode model
Remote Diode TruTherm
Mode Control
07h
01h
8
Enables or disables TruTherm
technology for Remote Diode
measurements
1-shot
0Fh
-
WO
-
Activates one conversion for
all 3 channels if the chip is in
standby mode (i.e.
RUN/STOP bit = 1). Data
transmitted by the host is
ignored by the LM95231.
Local Temperature MSB
10h
-
RO
8
Remote Temperature 1 MSB
11h
-
RO
8
Remote Temperature 2 MSB
12h
-
RO
8
Local Temperature LSB
20h
-
RO
2
All unused bits will report zero
Remote Temperature 1 LSB
21h
-
RO
3/5
All unused bits will report zero
Remote Temperature 2 LSB
22h
-
RO
3/5
All unused bits will report zero
Manufacturer ID
FEh
01h
RO
Revision ID
FFh
A1h
RO
13
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LM95231
1.0 Functional Description
LM95231
2.0 LM95231 Registers
(Continued)
2.1 STATUS REGISTER
(Read Only Address 02h):
D7
D6
Busy
D5
D4
Reserved
0
0
D3
D2
D1
D0
R2TME
R1TME
RD2M
RD1M
0
Bits
Name
Description
7
Busy
When set to "1" the part is converting.
6-4
Reserved
Reports "0" when read.
3
Remote 2 TruTherm Mode
Enabled (R2TME)
When set to "1" indicates that the TruTherm Mode has been activated
for Remote diode 2. After being enabled TruTherm Mode will take at
most one conversion cycle to be fully active.
2
Remote 1 TruTherm Mode
Enabled (R2TME)
When set to "1" indicates that the TruTherm Mode has been activated
for Remote diode 1. After being enabled TruTherm Mode will take at
most one conversion cycle to be fully active.
1
Remote Diode 2 Missing (RD2M)
When set to "1" Remote Diode 2 is missing. (i.e. D2+ shorted to VDD,
Ground or D2-, or D2+ is floating). Temperature Reading is FFE0h
which converts to 255.875 ˚C if unsigned format is selected or 8000h
which converts to –128.000 ˚C if signed format is selected. Note,
connecting a 2N3904 transistor to Remote 2 inputs with TruTherm
mode active may also cause this bit to be set.
0
Remote Diode 1 Missing (RD1M)
When set to "1" Remote Diode 1 is missing. (i.e. D1+ shorted to VDD,
Ground or D1-, or D1+ is floating). Temperature Reading is FFE0h
which converts to 255.875 ˚C if unsigned format is selected or 8000h
which converts to –128.000 ˚C if signed format is selected. Note,
connecting a 2N3904 transistor to Remote 1 inputs with TruTherm
mode active may also cause this bit to be set.
2.2 CONFIGURATION REGISTER
(Read Address 03h /Write Address 03h):
D7
D6
D5
D4
D3
D2
D1
D0
0
RUN/STOP
CR1
CR0
0
R2DF
R1DF
0
Bits
Name
Description
7
Reserved
Reports "0" when read.
6
RUN/STOP
Logic 1 disables the conversion and puts the part in standby mode.
Conversion can be activated by writing to one-shot register.
5-4
Conversion Rate (CR1:CR0)
00: continuous mode 75.8 ms, 13.2 Hz (typ), when diode mode is
selected for both remote channels; 77.5 ms, 12.9 Hz (typ), when
TruTherm Mode is enabled for one remote channel.
01: converts every 182 ms, 5.5 Hz (typ)
10: converts every 1 second, 1 Hz (typ)
11: converts every 2.7 seconds, 0.37 Hz (typ)
Note: typically a remote diode conversion takes 30 ms with diode
mode is selected; when the TruTherm Mode is selected a conversion
takes an additional 1.7 ms; a local conversion takes 15.8 ms.
3
Reserved
Reports "0" when read.
2
Remote 2 Data Format (R2DF)
Logic 0: unsigned Temperature format (0 ˚C to +255.875 ˚C)
Logic 1: signed Temperature format (-128 ˚C to +127.875 ˚C)
1
Remote 1 Data Format (R1DF)
Logic 0: unsigned Temperature format (0 ˚C to +255.875 ˚C)
Logic 1: signed Temperature format (-128 ˚C to +127.875 ˚C)
0
Reserved
Reports "0" when read.
Power up default is with all bits “0” (zero)
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14
LM95231
2.0 LM95231 Registers
(Continued)
2.3 REMOTE DIODE FILTER CONTROL REGISTER
(Read/write Address 06h):
D7
D6
D5
D4
D3
D2
D1
D0
0
0
0
0
0
R2FE
0
R1FE
Bits
Name
7-3
Reserved
Description
Reports "0" when read.
2
Remote 2 Filter Enable (R2FE)
0: Filter Off
1: Noise Filter On
1
Reserved
Reports "0" when read.
0
Remote 1 Filter Enable (R1FE)
0: Filter Off
1: Noise Filter On
Power up default is 05h.
2.4 REMOTE DIODE MODEL TYPE SELECT REGISTER
(Read/Write Address 30h):
D7
D6
D5
D4
D3
D2
D1
D0
0
0
0
0
0
R2MS
0
R1MS
Bits
Name
Description
7-3
Reserved
Reports "0" when read.
2
Remote Diode 2 Model Select
(R2MS)
0: 2N3904 model (make sure TruTherm mode is disabled)
1: Pentium 4 processor on 90nm process model (make sure TruTherm
mode is enabled)
Power up default is 0.
1
Reserved
Reports "0" when read.
0
Remote Diode 1 Model Select
(R1MS)
0: 2N3904 model (make sure TruTherm mode is disabled)
1: Pentium 4 processor on 90nm process model (make sure TruTherm
mode is enabled)
Power up default is 1.
Power up default is 01h.
2.5 REMOTE TruTherm MODE CONTROL
(Read/Write Address 07h):
D7
D6
D5
D4
D3
D2
D1
D0
Reserved
R2M2
R2M1
R2M0
Reserved
R1M2
R1M1
R1M0
Bits
Description
7
Reserved
Must be left at 0.
6-4
R2M2:R2M0
000: Remote 2 TruTherm Mode disabled; used when measuring
MMBT3904 transistors
001: Remote 2 TruTherm Mode enabled; used when measuring
Processors
111: Remote 2 TruTherm Mode enabled; used when measuring
Processors
Note, all other codes provide unspecified results and should not be
used.
3
Reserved
Must be left at 0.
15
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LM95231
2.0 LM95231 Registers
Bits
Description
2-0
R1M2:R1M0
(Continued)
000: Remote 1 TruTherm Mode disabled; used when measuring
MMBT3904 transistors
001: Remote 1 TruTherm Mode enabled; used when measuring
Processors
111: Remote 1 TruTherm Mode enabled; used when measuring
Processors
Note, all other codes provide unspecified results and should not be
used.
Power up default is 01h.
2.6 LOCAL and REMOTE MSB and LSB TEMPERATURE REGISTERS
Local Temperature MSB
(Read Only Address 10h) 9-bit plus sign format:
BIT
D7
D6
D5
D4
D3
D2
D1
D0
Value
SIGN
64
32
16
8
4
2
1
Temperature Data: LSb = 1˚C.
Local Temperature LSB
(Read Only Address 20h) 9-bit plus sign format:
BIT
D7
D6
D5
D4
D3
D2
D1
D0
Value
0.5
0.25
0
0
0
0
0
0
Temperature Data: LSb = 0.25˚C.
Remote Temperature MSB
(Read Only Address 11h, 12h) 10 bit plus sign format:
BIT
D7
D6
D5
D4
D3
D2
D1
D0
Value
SIGN
64
32
16
8
4
2
1
Temperature Data: LSb = 1˚C.
(Read Only Address 11h, 12h) 11-bit unsigned format:
BIT
D7
D6
D5
D4
D3
D2
D1
D0
Value
128
64
32
16
8
4
2
1
Temperature Data: LSb = 1˚C.
Remote Temperature LSB
(Read Only Address 21, 22h) 10-bit plus sign or 11-bit unsigned binary
formats with filter off:
BIT
D7
D6
D5
D4
D3
D2
D1
D0
Value
0.5
0.25
0.125
0
0
0
0
0
Temperature Data: LSb = 0.125˚C or 1/8˚C.
12-bit plus sign or 13-bit unsigned binary formats with filter on:
BIT
D7
D6
D5
D4
D3
D2
D1
D0
Value
0.5
0.25
0.125
0.0625
0.03125
0
0
0
Temperature Data: LSb = 0.03125˚C or 1/32˚C.
For data synchronization purposes, the MSB register should be read first if the user wants to read both MSB and LSB registers.
The LSB will be locked after the MSB is read. The LSB will be unlocked after being read. If the user reads MSBs consecutively,
each time the MSB is read, the LSB associated with that temperature will be locked in and override the previous LSB value
locked-in.
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16
LM95231
2.0 LM95231 Registers
(Continued)
2.7 MANUFACTURERS ID REGISTER
(Read Address FEh) The default value is 01h.
2.8 DIE REVISION CODE REGISTER
(Read Address FFh) The default value is A1h. This register will increment by 1 every time there is a revision to the die by National
Semiconductor.
•
•
•
•
3.0 Applications Hints
The LM95231 can be applied easily in the same way as
other integrated-circuit temperature sensors, and its remote
diode sensing capability allows it to be used in new ways as
well. It can be soldered to a printed circuit board, and because the path of best thermal conductivity is between the
die and the pins, its temperature will effectively be that of the
printed circuit board lands and traces soldered to the
LM95231’s pins. This presumes that the ambient air temperature is almost the same as the surface temperature of
the printed circuit board; if the air temperature is much higher
or lower than the surface temperature, the actual temperature of the LM95231 die will be at an intermediate temperature between the surface and air temperatures. Again, the
primary thermal conduction path is through the leads, so the
circuit board temperature will contribute to the die temperature much more strongly than will the air temperature.
To measure temperature external to the LM95231’s die, use
a remote diode. This diode can be located on the die of a
target IC, allowing measurement of the IC’s temperature,
independent of the LM95231’s temperature. A discrete diode
can also be used to sense the temperature of external
objects or ambient air. Remember that a discrete diode’s
temperature will be affected, and often dominated, by the
temperature of its leads. Most silicon diodes do not lend
themselves well to this application. It is recommended that
an MMBT3904 transistor base emitter junction be used with
the collector tied to the base.
The LM95231’s TruTherm technology allows accurate sensing of integrated thermal diodes, such as those found on
processors. With TruTherm technology turned off, the
LM95231 can measure a diode connected transistor such as
the MMBT3904.
The LM95231 has been optimized to measure the remote
thermal diode integrated in a Pentium 4 processor on 90nm
process or an MMBT3904 transistor. Using the Remote Diode Model Select register either pair of remote inputs can be
assigned to be either a Pentium 4 processor on 90nm process or an MMBT3904.
q = 1.6x10−19 Coulombs (the electron charge),
T = Absolute Temperature in Kelvin
k = 1.38x10−23joules/K (Boltzmann’s constant),
η is the non-ideality factor of the process the diode is
manufactured on,
IS = Saturation Current and is process dependent,
•
• If= Forward Current through the base emitter junction
• VBE = Base Emitter Voltage drop
In the active region, the -1 term is negligible and may be
eliminated, yielding the following equation
(2)
In Equation (2), η and IS are dependant upon the process
that was used in the fabrication of the particular diode. By
forcing two currents with a very controlled ratio (IF2/IF1) and
measuring the resulting voltage difference, it is possible to
eliminate the IS term. Solving for the forward voltage difference yields the relationship:
(3)
Solving Equation (3) for temperature yields:
(4)
Equation (4) holds true when a diode connected transistor
such as the MMBT3904 is used. When this “diode” equation
is applied to an integrated diode such as a processor transistor with its collector tied to GND as shown in Figure 3 it
will yield a wide non-ideality spread. This wide non-ideality
spread is not due to true process variation but due to the fact
that Equation (4) is an approximation.
TruTherm technology uses the transistor equation, Equation
(5), which is a more accurate representation of the topology
of the thermal diode found in an FPGA or processor.
3.1 DIODE NON-IDEALITY
3.1.1 Diode Non-Ideality Factor Effect on Accuracy
When a transistor is connected as a diode, the following
relationship holds for variables VBE, T and IF:
(5)
(1)
where:
17
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LM95231
3.0 Applications Hints
(Continued)
20120243
FIGURE 3. Thermal Diode Current Paths
Solving Equation (6) for RPCB equal to +0.264Ω and
−0.088Ω results in the additional error due to the spread in
the series resistance of +0.16˚C to −0.05˚C. The spread in
error cannot be canceled out, as it would require measuring
each individual thermal diode device. This is quite difficult
and impractical in a large volume production environment.
Equation (6) can also be used to calculate the additional
error caused by series resistance on the printed circuit
board. Since the variation of the PCB series resistance is
minimal, the bulk of the error term is always positive and can
simply be cancelled out by subtracting it from the output
readings of the LM95231.
TruTherm should only be enabled when measuring the temperature of a transistor integrated as shown in the processor
of Figure 3, because Equation (5) only applies to this topology.
3.1.2 Calculating Total System Accuracy
The voltage seen by the LM95231 also includes the IFRS
voltage drop of the series resistance. The non-ideality factor,
η, is the only other parameter not accounted for and depends on the diode that is used for measurement. Since
∆VBE is proportional to both η and T, the variations in η
cannot be distinguished from variations in temperature.
Since the non-ideality factor is not controlled by the temperature sensor, it will directly add to the inaccuracy of the
sensor. For the Pentium 4 processor on 90nm process, Intel
specifies a +1.19%/−0.27% variation in η from part to part
when the processor diode is measured by a circuit that
assumes diode equation, Equation (4), as true. As an example, assume a temperature sensor has an accuracy
specification of ± 0.75˚C at a temperature of 65 ˚C (338
Kelvin) and the processor diode has a non-ideality variation
of +1.19%/−0.27%. The resulting system accuracy of the
processor temperature being sensed will be:
TACC = ± 0.75˚C + (+1.19% of 338 K) = +4.76 ˚C
and
TACC = ± 0.75˚C + (−0.27% of 338 K) = −1.65 ˚C
TrueTherm technology uses the transistor equation, Equation (5), resulting in a non-ideality spread that truly reflects
the process variation which is very small. The transistor
equation non-ideality spread is ± 0.1% for the Pentium 4
processor on 90nm process. The resulting accuracy when
using TruTherm technology improves to:
TACC = ± 0.75˚C + ( ± 0.1% of 338 K) = ± 1.08 ˚C
The next error term to be discussed is that due to the series
resistance of the thermal diode and printed circuit board
traces. The thermal diode series resistance is specified on
most processor data sheets. For the Pentium 4 processor on
90 nm process, this is specified at 3.33Ω typical. The
LM95231 accommodates the typical series resistance of the
Pentium 4 processor on 90 nm process. The error that is not
accounted for is the spread of the Pentium’s series resistance, that is 3.242Ω to 3.594Ω or +0.264Ω to −0.088Ω. The
equation to calculate the temperature error due to series
resistance (TER) for the LM95231 is simply:
Processor Family
min
Pentium III CPUID 67h
1
typ
Series
R
max
1.0065 1.0125
Pentium III CPUID
68h/PGA370Socket/
Celeron
1.0057
Pentium 4, 423 pin
0.9933 1.0045 1.0368
Pentium 4, 478 pin
0.9933 1.0045 1.0368
Pentium 4 on 0.13
micron process,
2-3.06GHz
1.0011 1.0021 1.0030 3.64 Ω
Pentium 4 on 90 nm
process
1.0083
Pentium M Processor
(Centrino)
AMD Athlon MP model
6
1.008
1.011
1.0125
1.023 3.33 Ω
1.00151 1.00220 1.00289 3.06 Ω
MMBT3904
1.003
1.002
1.008
1.016
AMD Athlon 64
1.008
1.008
1.096
AMD Opteron
1.008
1.008
1.096
AMD Sempron
1.00261
0.93 Ω
3.1.3 Compensating for Different Non-Ideality
In order to compensate for the errors introduced by nonideality, the temperature sensor is calibrated for a particular
processor. National Semiconductor temperature sensors are
always calibrated to the typical non-ideality and series resistance of a given processor type. The LM95231 is calibrated
for two non-ideality factors and series resistance values thus
(6)
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Diode Equation ηD,
non-ideality
18
1.
VDD should be bypassed with a 0.1µF capacitor in parallel with 100pF. The 100pF capacitor should be placed
as close as possible to the power supply pin. A bulk
capacitance of approximately 10µF needs to be in the
near vicinity of the LM95231.
2. A 100pF diode bypass capacitor is recommended to
filter high frequency noise but may not be necessary.
Make sure the traces to the 100pF capacitor are
matched. Place the filter capacitors close to the
LM95231 pins.
(Continued)
supporting the MMBT3904 transistor and the Pentium 4
processor on 90nm process without the requirement for
additional trims. For most accurate measurements TruTherm
mode should be turned on when measuring the Pentium 4
processor on the 90nm process to minimize the error introduced by the false non-ideality spread (see Section 3.1.1
Diode Non-Ideality Factor Effect on Accuracy). When a temperature sensor calibrated for a particular processor type is
used with a different processor type, additional errors are
introduced.
3.
Temperature errors associated with non-ideality of different
processor types may be reduced in a specific temperature
range of concern through use of software calibration. Typical
Non-ideality specification differences cause a gain variation
of the transfer function, therefore the center of the temperature range of interest should be the target temperature for
calibration purposes. The following equation can be used to
calculate the temperature correction factor (TCF) required to
compensate for a target non-ideality differing from that supported by the LM95231.
(7)
TCF = [(ηS−ηProcessor) ÷ ηS] x (TCR+ 273 K)
where
• ηS = LM95231 non-ideality for accuracy specification
• ηT = target thermal diode typical non-ideality
Ideally, the LM95231 should be placed within 10cm of
the Processor diode pins with the traces being as
straight, short and identical as possible. Trace resistance of 1Ω can cause as much as 0.62˚C of error. This
error can be compensated by using simple software
offset compensation.
4.
Diode traces should be surrounded by a GND guard ring
to either side, above and below if possible. This GND
guard should not be between the D+ and D− lines. In the
event that noise does couple to the diode lines it would
be ideal if it is coupled common mode. That is equally to
the D+ and D− lines.
5. Avoid routing diode traces in close proximity to power
supply switching or filtering inductors.
6.
Avoid running diode traces close to or parallel to high
speed digital and bus lines. Diode traces should be kept
at least 2cm apart from the high speed digital traces.
7. If it is necessary to cross high speed digital traces, the
diode traces and the high speed digital traces should
cross at a 90 degree angle.
8. The ideal place to connect the LM95231’s GND pin is as
close as possible to the Processors GND associated
with the sense diode.
• TCR = center of the temperature range of interest in ˚C
The correction factor of Equation (7) should be directly
added to the temperature reading produced by the
LM95231. For example when using the LM95231, with the
3904 mode selected, to measure a AMD Athlon processor,
with a typical non-ideality of 1.008, for a temperature range
of 60 ˚C to 100 ˚C the correction factor would calculate to:
TCF=[(1.003−1.008)÷1.003]x(80+273) =−1.75˚C
Therefore, 1.75˚C should be subtracted from the temperature readings of the LM95231 to compensate for the differing
typical non-ideality target.
9.
Leakage current between D+ and GND and between D+
and D− should be kept to a minimum. Thirteen nanoamperes of leakage can cause as much as 0.2˚C of
error in the diode temperature reading. Keeping the
printed circuit board as clean as possible will minimize
leakage current.
Noise coupling into the digital lines greater than 400mVp-p
(typical hysteresis) and undershoot less than 500mV below
GND, may prevent successful SMBus communication with
the LM95231. SMBus no acknowledge is the most common
symptom, causing unnecessary traffic on the bus. Although
the SMBus maximum frequency of communication is rather
low (100kHz max), care still needs to be taken to ensure
proper termination within a system with multiple parts on the
bus and long printed circuit board traces. An RC lowpass
filter with a 3db corner frequency of about 40MHz is included
on the LM95231’s SMBCLK input. Additional resistance can
be added in series with the SMBDAT and SMBCLK lines to
further help filter noise and ringing. Minimize noise coupling
by keeping digital traces out of switching power supply areas
as well as ensuring that digital lines containing high speed
data communications cross at right angles to the SMBDAT
and SMBCLK lines.
3.2 PCB LAYOUT FOR MINIMIZING NOISE
20120217
FIGURE 4. Ideal Diode Trace Layout
In a noisy environment, such as a processor mother board,
layout considerations are very critical. Noise induced on
traces running between the remote temperature diode sensor and the LM95231 can cause temperature conversion
errors. Keep in mind that the signal level the LM95231 is
trying to measure is in microvolts. The following guidelines
should be followed:
19
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LM95231
3.0 Applications Hints
LM95231 Precision Dual Remote Diode Temperature Sensor with SMBus Interface and TruTherm
Technology
Physical Dimensions
inches (millimeters) unless otherwise noted
8-Lead Molded Mini-Small-Outline Package (MSOP),
JEDEC Registration Number MO-187
Order Number LM95231BIMM, LM95231BIMMX, LM95231BIMM-1, LM95231BIMMX-1, LM95231BIMM-2,
LM95231BIMMX-2,
LM95231CIMM, LM95231CIMMX, LM95231CIMM-1, LM95231CIMMX-1, LM95231CIMM-2 or LM95231CIMMX-2
NS Package Number MUA08A
National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves
the right at any time without notice to change said circuitry and specifications.
For the most current product information visit us at www.national.com.
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