NSC LM95241CIMM-1

LM95241
Dual Remote Diode Temperature Sensor with SMBus
Interface and TruTherm™ Technology (65nm/90nm)
General Description
The LM95241 is a precision dual remote diode temperature
sensor (RDTS) that uses National’s TruTherm technology.
The 2-wire serial interface of the LM95241 is compatible with
SMBus 2.0. The LM95241 can sense three temperature
zones, it can measure the temperature of its own die as well
as two diode connected transistors. The LM95241 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 such as 90nm and 65nm. The LM95241 supports
user selectable thermal diode non-ideality of either Intel
processor on 90nm or 65nm process or 2N3904.
The LM95241 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 LM95241 remote diode
readings can resolve temperatures above 127˚C. Local temperature readings have a resolution of 9-bits plus sign.
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 Diode Temperature Accuracy
± 1.25 ˚C (max)
± 2.5 ˚C (max)
TA=0˚C to 85˚C, TD=25˚C to 140˚C
TA=20˚C to 40˚C, TD=45˚C to 85˚C
j Local Temperature Accuracy
Features
TA=0˚C to 85˚C
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 processor on 65nm or 90nm process or 2N3904
non-ideality selection
n Remote diode fault detection
n On-board local temperature sensing
j Supply Voltage
j Average Supply Current
± 3.0 ˚C (max)
3.0 V to 3.6 V
471 µA (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
20199702
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
DS201997
www.national.com
LM95241 Dual Remote Diode Temperature Sensor with SMBus Interface and TruTherm
Technology (65nm/90nm)
September 2006
LM95241
Ordering Information
Package
Marking
NS Package
Number
Transport
Media
SMBus Device
Address
LM95241CIMM
T28C
MUA08A (MSOP-8)
1000 Units on Tape
and Reel
010 1011
LM95241CIMMX
T28C
MUA08A (MSOP-8)
3500 Units on Tape
and Reel
010 1011
LM95241CIMM-1
T29C
MUA08A (MSOP-8)
1000 Units on Tape
and Reel
001 1001
LM95241CIMMX-1
T29C
MUA08A (MSOP-8)
3500 Units on Tape
and Reel
001 1001
LM95241CIMM-2
T30C
MUA08A (MSOP-8)
1000 Units on Tape
and Reel
010 1010
LM95241CIMMX-2
T30C
MUA08A (MSOP-8)
3500 Units on Tape
and Reel
010 1010
Part Number
Pin Descriptions
Label
Pin #
D1+
1
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 D1+ and D1-. A 100 pF
capacitor between D1+ and D1− can be added and
may improve performance in noisy systems.
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
www.national.com
Function
Typical Connection
2
LM95241
Simplified Block Diagram
20199701
Typical Application
20199703
3
www.national.com
LM95241
Absolute Maximum Ratings (Note 1)
Supply Voltage
Charged Device Model Model
−0.3 V to 6.0 V
Voltage at SMBDAT, SMBCLK
Voltage at Other Pins
−0.5V to 6.0V
−0.3 V to (VDD + 0.3 V)
Soldering process must comply with National’s reflow
temperature profile specifications. Refer to
http://www.national.com/packaging/. (Note 5)
Input Current at All Pins (Note 2)
± 5 mA
Package Input Current (Note 2)
30 mA
Operating Ratings
SMBDAT Output Sink Current
10 mA
(Notes 1, 3)
Junction Temperature (Note 3)
+125˚C
Storage Temperature
−65˚C to +150˚C
ESD Susceptibility (Note 4)
Human Body Model
Machine Model
2000 V
200 V
1000 V
Operating Temperature Range
0˚C to +125˚C
Electrical Characteristics
Temperature Range
TMIN≤TA≤TMAX
LM95241CIMM
0˚C≤TA≤+85˚C
Supply Voltage Range (VDD)
+3.0V to +3.6V
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 LM95241. TD is the
junction temperature of the remote thermal diode.
Parameter
Conditions
Typical
Limits
Units
(Note 6)
(Note 7)
(Limit)
±1
±3
˚C (max)
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
± 1.25
˚C (max)
TA = +0˚C to
+85˚C
TD = +25˚C
to +140˚C
± 2.5
˚C (max)
Remote Diode Measurement Resolution with
filtering turned off
10+sign/11
0.125
˚C
Remote Diode Measurement Resolution with digital
filtering turned on
12+sign/13
Bits
0.03125
˚C
9+sign
Bits
Local Diode Measurement Resolution
Bits
0.25
Conversion Time of All Temperatures at the
Fastest Setting (Note 11)
Average Quiescent Current (Note 10)
76.5
86.1
ms (max)
TruTherm Mode Enabled for All
Remote Channels
79.1
88.9
ms (max)
SMBus Inactive, 1 Hz conversion
rate
471
640
µA (max)
Shutdown
356
µA
0.4
V
D− Source Voltage
Diode Source Current Ratio
Diode Source Current
16
(VD+ − VD−)=+ 0.65V; high-level
Low-level
Power-On Reset Threshold
www.national.com
˚C
TruTherm Mode Disabled for All
Remote Channels
172
230
µA (max)
100
µA (min)
2.7
1.6
V (max)
V (min)
11
Measure on VDD input, falling
edge
4
µA
LM95241
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 LM95241 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 LM95241. 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
Units
(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
µs (max)
µs (min)
tF,SMB
SMBus Fall Time
(Note 13)
0.3
µs (max)
tOF
Output Fall Time
CL = 400pF,
IO = 3mA, (Note 13)
250
ns (max)
tTIMEOUT SMBDAT and SMBCLK Time Low for Reset of
Serial Interface (Note 14)
25
35
ms (min)
ms (max)
tSU;DAT
Data In Setup Time to SMBCLK High
250
ns (min)
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
5
www.national.com
LM95241
Logic Electrical Characteristics
(Continued)
SMBus Communication
20199709
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 conditions 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 LM95241’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.
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
All Input ESD Protection Structure Circuits
Circuit A
Circuit B
Circuit C
Note 3: Thermal resistance junction-to-ambient when attached to a printed circuit board with 1oz. foil and no air flow:
– MSOP-8 = 210˚C/W
Note 4: Human body model (HBM), 100pF discharged through a 1.5kΩ resistor. Machine model (MM), 200pF discharged directly into each pin. Charged Device
Model (CDM) simulates a pin slowly acquiring charge (such as from a device sliding down the feeder in an automated assembler) then rapidly being discharged.
Note 5: Reflow temperature profiles are different for packages containing lead (Pb) than for those that do not.
Note 6: Typical figures are at TA = 25˚C and represent most likely parametric norms at the 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 LM95241 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 LM95241CIMM is guaranteed when using a typical thermal diode of an Intel processor on a 65 nm process or an MMBT3904
diode-connected transistor, as selected in the Remote Diode Model Select register. See typical performance curve for performance with Intel processor on a 90nm
process.
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 LM95241 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 LM95241’s SMBus state machine, therefore setting
SMBDAT and SMBCLK pins to a high impedance state.
www.national.com
6
Intel Processor on 65nm Process or 90nm Process
Thermal Diode Performance Comparison
Thermal Diode Capacitor or PCB Leakage Current Effect
Remote Diode Temperature Reading
20199704
20199705
Remote Temperature Reading Sensitivity to Thermal
Diode Filter Capacitance
Conversion Rate Effect on Average Power Supply
Current
20199707
20199706
The 2-wire serial interface, of the LM95241, 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 LM95241
to the system requirements. The LM95241 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 LM95241 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 LM95241 can support two
external transistor types, a Intel processor on 65nm or 90mn
process thermal diode or a 2N3904 diode connected transistor. The transistor type is register programmable and does
not require software intervention after initialization. The
LM95241 has an advanced input stage using National Semiconductor’s TruTherm technology that reduces the spread in
non-ideality found in Intel processors on 65nm or 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.
7
www.national.com
LM95241
Typical Performance Characteristics
LM95241
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 LM95241 remote diode temperature accuracy is
trimmed for the typical thermal diode of a Intel processor on
65nm or 90nm process or a typical 2N3904 transistor and
the accuracy is guaranteed only when using either of these
diodes when selected appropriately. TruTherm mode should
be enabled when measuring a Intel processor on 65nm or
90nm process and disabled when measuring a 3904 transistor.
Diode fault detection circuitry in the LM95241 can detect the
presence of a remote diode.
The LM95241 register set has an 8-bit data structure and
includes:
1.
Most-Significant-Byte (MSB) Local Temperature Register
2.
Least-Significant-Byte (LSB) Local Temperature Register
3.
4.
MSB Remote Temperature 1 Register
LSB Remote Temperature 1 Register
5.
6.
7.
MSB Remote Temperature 2 Register
LSB Remote Temperature 2 Register
Status Register: busy, diode fault
8.
Configuration Register: resolution control, conversion
rate control, standby control
Remote Diode Filter Setting
Remote Diode Model Select
Remote Diode TruTherm Mode Control
1-shot Register
9.
10.
11.
12.
20199706
FIGURE 1. Conversion Rate Effect on Power Supply
Current
1.2 POWER-ON-DEFAULT STATES
LM95241 always powers up to these known default states.
The LM95241 remains in these states until after the first
conversion.
1.
2.
3.
4.
5.
13. Manufacturer ID
14. Revision ID
1.1 CONVERSION SEQUENCE
In the power up default state the LM95241 typically takes
77.8 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 88.9 ms. Different conversion
rates will cause the LM95241 to draw different amounts of
supply current as shown in Figure 1.
6.
7.
Command Register set to 00h
Local Temperature set to 0˚C until the end of the first
conversion
Remote Diode Temperature set to 0˚C until the end of
the first conversion
Remote Diode digital filters are on.
Remote Diode 1 model is set to Intel processor on 65nm
or 90nm process with TruTherm Mode enabled. Remote
Diode 2 model is set to 2N3904/MMBT3904 with TruTherm mode disabled.
Status Register depends on state of thermal diode inputs
Configuration register set to 00h; continuous conversion
1.3 SMBus INTERFACE
The LM95241 operates as a slave on the SMBus, so the
SMBCLK line is an input and the SMBDAT line is bidirectional. The LM95241 never drives the SMBCLK line and it
does not support clock stretching. According to SMBus
specifications, the LM95241 has a 7-bit slave address. All
bits A6 through A0 are internally programmed and cannot be
changed by software or hardware. The SMBus slave address is dependent on the LM95241 part number ordered:
Version
A6 A5 A4 A3 A2 A1 A0
LM95241CIMM
0
1
0
1
0
1
1
LM95241CIMM-1
0
0
1
1
0
0
1
LM95241CIMM-2
0
1
0
1
0
1
0
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
www.national.com
8
(Continued)
Temperature
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
Digital Output
Binary
Hex
+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
0000 0001 0000 0000
0100h
Binary
Hex
+1˚C
+125˚C
0111 1101 0000 0000
7D00h
+0.03125˚C
0000 0000 0000 1000
0008h
+25˚C
0001 1001 0000 0000
1900h
0˚C
0000 0000 0000 0000
0000h
+1˚C
0000 0001 0000 0000
0100h
+0.125˚C
0000 0000 0010 0000
0020h
0˚C
0000 0000 0000 0000
0000h
−0.125˚C
1111 1111 1110 0000
FFE0h
−1˚C
1111 1111 0000 0000
FF00h
−25˚C
1110 0111 0000 0000
E700h
−55˚C
1100 1001 0000 0000
C900h
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.
Temperature
11-bit, unsigned binary
Temperature
+255.875˚C
Digital Output
Digital Output
Binary
Hex
+125˚C
0111 1101 0000 0000
7D00h
+25˚C
0001 1001 0000 0000
1900h
Binary
Hex
+1˚C
0000 0001 0000 0000
0100h
1111 1111 1110 0000
FFE0h
+0.25˚C
0000 0000 0100 0000
0040h
+255˚C
1111 1111 0000 0000
FF00h
0˚C
0000 0000 0000 0000
0000h
+201˚C
1100 1001 0000 0000
C900h
−0.25˚C
1111 1111 1100 0000
FFC0h
+125˚C
0111 1101 0000 0000
7D00h
−1˚C
1111 1111 0000 0000
FF00h
+25˚C
0001 1001 0000 0000
1900h
−25˚C
1110 0111 0000 0000
E700h
+1˚C
0000 0001 0000 0000
0100h
−55˚C
1100 1001 0000 0000
C900h
+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
LM95241. The maximum resistance of the pull-up to provide
a 2.1V high level, based on LM95241 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
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
+0.03125˚C
0000 0000 0000 1000
0008h
0˚C
0000 0000 0000 0000
0000h
−0.03125˚C
1111 1111 1111 0111
FFF7h
−1˚C
1111 1111 0000 0000
FF00h
−25˚C
1110 0111 0000 0000
E700h
−55˚C
1100 1001 0000 0000
C900h
1.6 DIODE FAULT DETECTION
The LM95241 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.
1.7 COMMUNICATING WITH THE LM95241
The data registers in the LM95241 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 LM95241 falls into one
of four types of user accessibility:
1. Read only
13-bit, unsigned binary
Temperature
+255.875˚C
Digital Output
Binary
Hex
1111 1111 1110 0000
FFE0h
9
www.national.com
LM95241
1.0 Functional Description
LM95241
1.0 Functional Description
2.
Write only
3.
4.
Write/Read same address
Write/Read different address
The data byte has the most significant bit first. At the end of
a read, the LM95241 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)
A Write to the LM95241 will always include the address byte
and the command byte. A write to any register requires one
data byte.
Reading the LM95241 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
Register will point to one of the Read Temperature Registers because that will be the data most frequently read
from the LM95241), 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.
www.national.com
10
LM95241
1.0 Functional Description
(Continued)
20199711
(a) Serial Bus Write to the Internal Command Register
20199710
(b) Serial Bus Write to the internal Command Register followed by a Data Byte
20199712
(c) Serial Bus byte Read from a Register with the internal Command Register preset to desired value.
20199714
(d) Serial Bus Write followed by a Repeat Start and Immediate Read
FIGURE 2. SMBus Timing Diagrams for Access of Data
11
www.national.com
LM95241
1.0 Functional Description
2.
(Continued)
1.8 SERIAL INTERFACE RESET
In the event that the SMBus Master is RESET while the
LM95241 is transmitting on the SMBDAT line, the LM95241
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 LM95241 will respond properly to an
SMBus start condition at any point during the communication. After the start the LM95241 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 LM95241 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 LM95241 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 Intel
processor on 65nm or 90nm
process thermal diode model
Remote Diode TruTherm
Mode Control
07h
01h
6
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 LM95241.
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
A4h
RO
www.national.com
12
LM95241
2.0 LM95241 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. This bit will be set even if
the diode is desconnected.
2
Remote 1 TruTherm Mode
Enabled (R1TME)
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. This bit will be set even if
the diode is disconnected.
1
Remote Diode 2 Missing (RD2M)
When set to "1" Remote Diode 2 is missing. (See Section 1.6 for
further details.) 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 3904
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. (See Section 1.6 for
further details.) 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 3904
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 76.5 ms, 13.1 Hz (typ), when TruTherm Mode is
disabled (Diode Equation) for both remote channels; 77.8 ms, 12.9 Hz
(typ), when TruTherm Mode is enabled (Transistor Equation) 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)
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)
13
www.national.com
LM95241
2.0 LM95241 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 1Filter 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: Intel processor on 65nm or 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: Intel processor on 65nm or 90nm process model (make sure
TruTherm mode is enabled)
Power up default is 1.
Power up default is 01h.
2.5 REMOTE DIODE 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.
www.national.com
14
Bits
Description
2-0
R1M2:R1M0
LM95241
2.0 LM95241 Registers
(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.
15
www.national.com
LM95241
2.0 LM95241 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 A4h. This register will increment by 1 every time there is a revision to the die by National
Semiconductor.
•
•
•
•
3.0 Applications Hints
The LM95241 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
LM95241’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 LM95241 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 LM95241’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 LM95241’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 a
2N3904 transistor base emitter junction be used with the
collector tied to the base.
The LM95241’s TruTherm technology allows accurate sensing of integrated thermal diodes, such as those found on
sub-micron geometry processors. With TruTherm technology turned off, the LM95241 can measure a diode connected transistor such as the 2N3904 or MMBT3904.
The LM95241 has been optimized to measure the remote
thermal diode integrated in a Intel processor on 65nm or
90nm process or an MMBT3904 transistor. Using the Remote Diode Model Select register either pair of remote inputs
can be assigned to measure either a Intel processor on
65nm or 90nm process or an MMBT3904 transistor.
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:
www.national.com
q = 1.6x10−19 Coulombs (the electron charge),
T = Absolute Temperature in Kelvin
16
LM95241
3.0 Applications Hints
(Continued)
20199743
FIGURE 3. Thermal Diode Current Paths
Solving Equation (6) for RPCB equal to ± 1.73Ω results in the
additional error due to the spread in the series resistance of
± 1.07˚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 LM95241.
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 LM95241 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 D processor on 65nm process, Intel
specifies a +4.06%/−0.89% 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 ± 1.25˚C at a temperature of 65 ˚C (338
Kelvin) and the processor diode has a non-ideality variation
of +4.06%/−0.89%. The resulting system accuracy of the
processor temperature being sensed will be:
TACC = + 1.25˚C + (+4.06% of 338 K) = +14.97 ˚C
and
TACC = - 1.25˚C + (−0.89% of 338 K) = −4.26 ˚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 ± 0.4% for the Pentium D
processor on 65nm process. The resulting accuracy when
using TruTherm technology improves to:
TACC = ± 1.25˚C + ( ± 0.4% of 338 K) = ± 2.60 ˚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 D processor
on 65 nm process, this is specified at 4.52Ω typical. The
LM95241 accommodates the typical series resistance of the
Pentium D processor on 65nm process. The error that is not
accounted for is the spread of the Pentium’s series resistance, that is 2.79Ω to 6.24Ω or ± 1.73Ω. The equation to
calculate the temperature error due to series resistance
(TER) for the LM95241 is simply:
Transistor Equation
nD, non-ideality
Processor Family
min
typ
Intel processor on
65nm process
0.997
1.001
Processor Family
Pentium III CPUID 67h
max
1.005 4.52 Ω
Diode Equation ηD,
non-ideality
min
1
typ
Series
R
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
1.011
1.023 3.33 Ω
Pentium on 65 nm
porcess
1.000
1.009
1.050 4.52 Ω
Pentium M Processor
(Centrino)
1.0125
1.00151 1.00220 1.00289 3.06 Ω
MMBT3904
AMD Athlon MP model
6
1.008
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
(6)
17
www.national.com
LM95241
3.0 Applications Hints
AMD Sempron
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 LM95241 can cause temperature conversion
errors. Keep in mind that the signal level the LM95241 is
trying to measure is in microvolts. The following guidelines
should be followed:
(Continued)
0.93 Ω
1.00261
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 LM95241 is calibrated
for two non-ideality factors and series resistance values thus
supporting the MMBT3904 transistor and the Intel processor
on 65nm or 90nm process without the requirement for additional trims. For most accurate measurements TruTherm
mode should be turned on when measuring the Intel processor on the 65nm or 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.
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 LM95241.
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
LM95241 pins.
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 LM95241.
(7)
TCF = [(ηS−ηProcessor) ÷ ηS] x (TCR+ 273 K)
where
• ηS = LM95241 non-ideality for accuracy specification
• ηT = target thermal diode typical non-ideality
• 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
LM95233. For example when using the LM95241, 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 LM95241 to compensate for the differing
typical non-ideality target.
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 LM95241’s GND pin is as
close as possible to the Processor’s GND that is associated with the sense diode.
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 LM95241. 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 LM95241’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
20199717
FIGURE 4. Ideal Diode Trace Layout
www.national.com
Ideally, the LM95241 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 1˚C of error. This
error can be compensated by using simple software
offset compensation.
18
inches (millimeters) unless otherwise noted
8-Lead Molded Mini-Small-Outline Package (MSOP),
JEDEC Registration Number MO-187
Order Number LM95241CIMM or LM95241CIMMX
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.
LIFE SUPPORT POLICY
NATIONAL’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS
WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT AND GENERAL COUNSEL OF NATIONAL SEMICONDUCTOR
CORPORATION. As used herein:
1. Life support devices or systems are devices or systems
which, (a) are intended for surgical implant into the body, or
(b) support or sustain life, and whose failure to perform when
properly used in accordance with instructions for use
provided in the labeling, can be reasonably expected to result
in a significant injury to the user.
2. A critical component is any component of a life support
device or system whose failure to perform can be reasonably
expected to cause the failure of the life support device or
system, or to affect its safety or effectiveness.
BANNED SUBSTANCE COMPLIANCE
National Semiconductor follows the provisions of the Product Stewardship Guide for Customers (CSP-9-111C2) and Banned Substances
and Materials of Interest Specification (CSP-9-111S2) for regulatory environmental compliance. Details may be found at:
www.national.com/quality/green.
Lead free products are RoHS compliant.
National Semiconductor
Americas Customer
Support Center
Email: [email protected]
Tel: 1-800-272-9959
www.national.com
National Semiconductor
Europe Customer Support Center
Fax: +49 (0) 180-530 85 86
Email: [email protected]
Deutsch Tel: +49 (0) 69 9508 6208
English Tel: +44 (0) 870 24 0 2171
Français Tel: +33 (0) 1 41 91 8790
National Semiconductor
Asia Pacific Customer
Support Center
Email: [email protected]
National Semiconductor
Japan Customer Support Center
Fax: 81-3-5639-7507
Email: [email protected]
Tel: 81-3-5639-7560
LM95241 Dual Remote Diode Temperature Sensor with SMBus Interface and TruTherm
Technology (65nm/90nm)
Physical Dimensions