LM95231CIMM

LM95231 Precision Dual Remote Diode Temperature Sensor with SMBus Interface and TruTherm Technology August 2006 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. 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 j Supply Voltage j Supply Current ± 0.75˚C (max) ± 3.0˚C (max) 3.0V to 3.6V 402µA (typ) 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 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 Ordering Information Part Number LM95231BIMM LM95231BIMMX LM95231BIMM-1 LM95231BIMMX-1 LM95231BIMM-2 LM95231BIMMX-2 LM95231CIMM LM95231CIMMX LM95231CIMM-1 LM95231CIMMX-1 LM95231CIMM-2 LM95231CIMMX-2 Package Marking T23B T23B T25B T25B T26B T26B T23C T23C T25C T25C T26C T26C NS Package Number MUA08A (MSOP-8) MUA08A (MSOP-8) MUA08A (MSOP-8) MUA08A (MSOP-8) MUA08A (MSOP-8) MUA08A (MSOP-8) MUA08A (MSOP-8) MUA08A (MSOP-8) MUA08A (MSOP-8) MUA08A (MSOP-8) MUA08A (MSOP-8) MUA08A (MSOP-8) Transport Media 1000 Units on Tape and Reel 3500 Units on Tape and Reel 1000 Units on Tape and Reel 3500 Units on Tape and Reel 1000 Units on Tape and Reel 3500 Units on Tape and Reel 1000 Units on Tape and Reel 3500 Units on Tape and Reel 1000 Units on Tape and Reel 3500 Units on Tape and Reel 1000 Units on Tape and Reel 3500 Units on Tape and Reel SMBus Device Address 010 1011 010 1011 001 1001 001 1001 010 1010 010 1010 010 1011 010 1011 001 1001 001 1001 010 1010 010 1010 Thermal Diode Accuracy ± 0.75 ± 0.75 ± 0.75 ± 0.75 ± 0.75 ± 0.75 ± 1.25 ± 1.25 ± 1.25 ± 1.25 ± 1.25 ± 1.25 Typical Application 20120203 Pin Descriptions Label D1+ Pin # 1 Function Diode Current Source Typical Connection 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. www.national.com 2 LM95231 Pin Descriptions Label D1− (Continued) Pin # 2 Function Diode Return Current Sink Typical Connection 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. 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. 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. System low noise ground 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. From and to Controller; may require an external pull-up resistor From Controller; may require an external pull-up resistor D2+ 3 Diode Current Source D2− 4 Diode Return Current Sink GND VDD 5 6 Power Supply Ground Positive Supply Voltage Input SMBDAT SMBCLK 7 8 SMBus Bi-Directional Data Line, Open-Drain Output SMBus Clock Input Simplified Block Diagram 20120201 3 www.national.com LM95231 Absolute Maximum Ratings (Note 1) Supply Voltage Voltage at SMBDAT, SMBCLK Voltage at Other Pins Input Current at All Pins (Note 2) Package Input Current (Note 2) SMBDAT Output Sink Current Junction Tempeature (Note 3) Storage Temperature ESD Susceptibility (Note 4) Human Body Model Machine Model 2000 V 200 V −0.3 V to 6.0 V −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) ± 5 mA 30 mA 10 mA 125˚C −65˚C to +150˚C Operating Ratings (Notes 1, 3) Operating Temperature Range Electrical Characteristics Temperature Range LM95231BIMM, LM95231CIMM Supply Voltage Range (VDD) 0˚C to +125˚C TMIN≤TA≤TMAX 0˚C≤TA≤+85˚C +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 LM95231. TD is the junction temperature of the remote thermal diode. Parameter Conditions Typical (Note 6) Accuracy Using Local Diode Accuracy Using Remote Diode, see(Note 9) for Thermal Diode Processor Type. TA = 0˚C to +85˚C, (Note 8) TA = +20˚C to +40˚C; TD = +45˚C to +85˚C TA = +20˚C to +40˚C; TD = +45˚C to +85˚C TA = +20˚C to +40˚C; TD = +45˚C to +85˚C Intel 90nm Thermal Diode MMBT3904 Thermal Diode Intel 90nm and MMBT3904 Thermal Diodes Intel 90nm and MMBT3904 Thermal Diodes 10+sign/11 0.125 12+sign/13 0.03125 9+sign 0.25 Conversion Time of All Temperatures at the Fastest Setting Average Quiescent Current (Note 10) (Note 11) TruTherm Mode Disabled TruTherm Mode enabled SMBus Inactive, 1 Hz conversion rate Shutdown D− Source Voltage Diode Source Current Ratio 75.8 79.2 402 272 0.4 16 83.9 87.7 545 83.9 87.7 545 LM95231 BIMM Limits (Note 7) LM95231 CIMM Limits (Note 7) Units (Limit) ˚C (max) ˚C (max) ±1 ±3 ± 0.75 ±3 ± 1.25 ˚C (max) ± 1.25 ˚C (max) TA = +0˚C to +85˚C; TD = +25˚C to +140˚C Remote Diode Measurement Resolution with filtering turned off Remote Diode Measurement Resolution with digital filtering turned on Local Diode Measurement Resolution ± 2.5 ± 2.5 ˚C (max) Bits ˚C Bits ˚C Bits ˚C ms (max) ms (max) µA (max) µA V www.national.com 4 LM95231 Temperature-to-Digital Converter Characteristics (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 Typical (Note 6) LM95231 BIMM Limits (Note 7) 300 100 11 2.7 1.8 2.7 1.8 LM95231 CIMM Limits (Note 7) 300 100 Units (Limit) µA (max) µA (min) µA V (max) V (min) Diode Source Current (VD+ − VD−) = + 0.65V; high-level Low-level Measure on VDD input, falling edge 176 Power-On Reset Threshold 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 (Note 6) SMBDAT, SMBCLK INPUTS VIN(1) VIN(0) VIN(HYST) IIN(1) IIN(0) CIN IOH VOL Logical “1” Input Voltage Logical “0”Input Voltage SMBDAT and SMBCLK Digital Input Hysteresis Logical “1” Input Current Logical “0” Input Current Input Capacitance High Level Output Current SMBus Low Level Output Voltage VOH = VDD IOL = 4mA IOL = 6mA VIN = VDD VIN = 0 V 400 0.005 −0.005 5 10 0.4 0.6 2.1 0.8 V (min) V (max) mV Limits (Note 7) Units (Limit) ± 10 ± 10 µA (max) µA (max) pF µA (max) V (max) SMBDAT OUTPUT 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 fSMB tLOW tHIGH tR,SMB tF,SMB tOF Parameter SMBus Clock Frequency SMBus Clock Low Time SMBus Clock High Time SMBus Rise Time SMBus Fall Time Output Fall Time from VIN(0)max to VIN(0)max from VIN(1)min to VIN(1)min (Note 12) (Note 13) CL = 400pF, IO = 3mA, (Note 13) 1 0.3 250 25 35 250 Conditions Typical (Note 6) Limits (Note 7) 100 10 4.7 25 4.0 Units (Limit) kHz (max) kHz (min) µs (min) ms (max) µs (min) µs (max) µs (max) ns (max) ms (min) ms (max) ns (min) tTIMEOUT SMBDAT and SMBCLK Time Low for Reset of Serial Interface (Note 14) tSU;DAT Data In Setup Time to SMBCLK High 5 www.national.com 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. Parameter Data Out Stable after SMBCLK Low Start Condition SMBDAT Low to SMBCLK Low (Start condition hold before the first clock falling edge) Stop Condition SMBCLK High to SMBDAT Low (Stop Condition Setup) SMBus Repeated Start-Condition Setup Time, SMBCLK High to SMBDAT Low SMBus Free Time Between Stop and Start Conditions SMBus Communication Conditions Typical (Note 6) Limits (Note 7) 300 1075 100 Units (Limit) ns (min) ns (max) ns (min) Symbol tHD;DAT tHD;STA tSU;STO tSU;STA tBUF 100 0.6 1.3 ns (min) µs (min) µs (min) 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. www.national.com 6 LM95231 Logic Electrical Characteristics Pin # 1 2 3 4 5 6 7 8 Label D1+ D1− D2+ D2− GND VDD SMBDAT SMBCLK Circuit A A A (Continued) Pin ESD Protection Structure Circuits Circuit C A Circuit A B B C C 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 www.national.com 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 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. 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 www.national.com 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. 8. 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 20120247 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 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 7. Configuration register set to 00h; continuous conversion, typical time = 85.8 ms when TruTherm Mode is enabled for Remote 1 only Configuration Register: resolution control, conversion rate control, standby control 9. Remote Diode Filter Setting 10. Remote Diode Model Select 11. Remote Diode TruTherm Mode Control 12. 1-shot Register 13. Manufacturer ID 14. Revision ID 1.1 CONVERSION SEQUENCE 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. 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 LM95231BIMM, LM95231CIMM LM95231BIMM-1, LM95231CIMM-1 LM95231BIMM-2, LM95231CIMM-2 A6 0 0 0 A5 1 0 1 A4 0 1 0 A3 1 1 1 A2 0 0 0 A1 A0 1 0 1 1 1 0 9 www.national.com LM95231 1.0 Functional Description 1.4 TEMPERATURE DATA FORMAT (Continued) Temperature +255.875˚C +255˚C +201˚C +125˚C +25˚C +1˚C +0.03125˚C 0˚C Hex 7D00h 1900h 0100h 0020h 0000h FFE0h FF00h E700h C900h +125˚C +25˚C +1˚C +0.25˚C 0˚C Hex FFE0h FF00h C900h 7D00h 1900h 0100h 0020h 0000h −0.25˚C −1˚C −25˚C −55˚C 13-bit, unsigned binary Digital Output Binary 1111 1111 1110 0000 1111 1111 0000 0000 1100 1001 0000 0000 0111 1101 0000 0000 0001 1001 0000 0000 0000 0001 0000 0000 0000 0000 0000 1000 0000 0000 0000 0000 Hex FFE0h FF00h C900h 7D00h 1900h 0100h 0008h 0000h 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 +125˚C +25˚C +1˚C +0.125˚C 0˚C −0.125˚C −1˚C −25˚C −55˚C Digital Output Binary 0111 1101 0000 0000 0001 1001 0000 0000 0000 0001 0000 0000 0000 0000 0010 0000 0000 0000 0000 0000 1111 1111 1110 0000 1111 1111 0000 0000 1110 0111 0000 0000 1100 1001 0000 0000 11-bit, unsigned binary Temperature +255.875˚C +255˚C +201˚C +125˚C +25˚C +1˚C +0.125˚C 0˚C Digital Output Binary 1111 1111 1110 0000 1111 1111 0000 0000 1100 1001 0000 0000 0111 1101 0000 0000 0001 1001 0000 0000 0000 0001 0000 0000 0000 0000 0010 0000 0000 0000 0000 0000 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 Digital Output Binary 0111 1101 0000 0000 0001 1001 0000 0000 0000 0001 0000 0000 0000 0000 0100 0000 0000 0000 0000 0000 1111 1111 1100 0000 1111 1111 0000 0000 1110 0111 0000 0000 1100 1001 0000 0000 Hex 7D00h 1900h 0100h 0040h 0000h FFC0h FF00h E700h C900h 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 +125˚C +25˚C +1˚C +0.03125˚C 0˚C −0.03125˚C −1˚C −25˚C −55˚C www.national.com 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%). 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 Binary 0111 1101 0000 0000 0001 1001 0000 0000 0000 0001 0000 0000 0000 0000 0000 1000 0000 0000 0000 0000 1111 1111 1111 1000 1111 1111 0000 0000 1110 0111 0000 0000 1100 1001 0000 0000 Hex 7D00h 1900h 0100h 0008h 0000h FFF8h FF00h E700h C900h 10 LM95231 1.0 Functional Description 1.7 COMMUNICATING with the LM95231 (Continued) 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 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. 11 www.national.com 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 www.national.com 12 LM95231 1.0 Functional Description 1.8 SERIAL INTERFACE RESET (Continued) 2. 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 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. 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. 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 Command (Hex) 02h 03h 06h 30h Power-On Default Value (Hex) 00h 05h 01h # of used bits 5 5 2 2 Name Status Register Configuration Register Remote Diode Filter Control Remote Diode Model Type Select Remote Diode TruTherm Mode Control 1-shot Read/Write RO R/W R/W R/W Comments 4 status bits and 1 busy bit Includes conversion rate control Controls thermal diode filter setting Selects the 2N3904 or Pentium 4 processor on 90nm process thermal diode model Enables or disables TruTherm technology for Remote Diode measurements 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. 07h 01h 8 0Fh - WO - Local Temperature MSB Remote Temperature 1 MSB Remote Temperature 2 MSB Local Temperature LSB Remote Temperature 1 LSB Remote Temperature 2 LSB Manufacturer ID Revision ID 10h 11h 12h 20h 21h 22h FEh FFh 01h A1h RO RO RO RO RO RO RO RO 8 8 8 2 3/5 3/5 All unused bits will report zero All unused bits will report zero All unused bits will report zero 13 www.national.com LM95231 2.0 LM95231 Registers 2.1 STATUS REGISTER (Read Only Address 02h): D7 Busy 0 Bits 7 6-4 3 Name Busy Reserved D6 (Continued) D5 Reserved 0 D4 0 Description D3 R2TME D2 R1TME D1 RD2M D0 RD1M When set to "1" the part is converting. Reports "0" when read. 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. 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. 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. 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. Remote 2 TruTherm Mode Enabled (R2TME) Remote 1 TruTherm Mode Enabled (R2TME) Remote Diode 2 Missing (RD2M) 2 1 0 Remote Diode 1 Missing (RD1M) 2.2 CONFIGURATION REGISTER (Read Address 03h /Write Address 03h): D7 0 Bits 7 6 5-4 D6 RUN/STOP Name Reserved RUN/STOP Conversion Rate (CR1:CR0) D5 CR1 D4 CR0 Description Reports "0" when read. Logic 1 disables the conversion and puts the part in standby mode. Conversion can be activated by writing to one-shot register. 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. Reports "0" when read. Logic 0: unsigned Temperature format (0 ˚C to +255.875 ˚C) Logic 1: signed Temperature format (-128 ˚C to +127.875 ˚C) Logic 0: unsigned Temperature format (0 ˚C to +255.875 ˚C) Logic 1: signed Temperature format (-128 ˚C to +127.875 ˚C) Reports "0" when read. D3 0 D2 R2DF D1 R1DF D0 0 3 2 1 0 Reserved Remote 2 Data Format (R2DF) Remote 1 Data Format (R1DF) Reserved Power up default is with all bits “0” (zero) www.national.com 14 LM95231 2.0 LM95231 Registers (Continued) 2.3 REMOTE DIODE FILTER CONTROL REGISTER (Read/write Address 06h): D7 0 Bits 7-3 2 1 0 D6 0 Name Reserved Remote 2 Filter Enable (R2FE) Reserved Remote 1 Filter Enable (R1FE) D5 0 D4 0 Description Reports "0" when read. 0: Filter Off 1: Noise Filter On Reports "0" when read. 0: Filter Off 1: Noise Filter On D3 0 D2 R2FE D1 0 D0 R1FE Power up default is 05h. 2.4 REMOTE DIODE MODEL TYPE SELECT REGISTER (Read/Write Address 30h): D7 0 Bits 7-3 2 D6 0 Name Reserved Remote Diode 2 Model Select (R2MS) D5 0 D4 0 Description Reports "0" when read. 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. Reports "0" when read. 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. D3 0 D2 R2MS D1 0 D0 R1MS 1 0 Reserved Remote Diode 1 Model Select (R1MS) Power up default is 01h. 2.5 REMOTE TruTherm MODE CONTROL (Read/Write Address 07h): D7 Reserved Bits 7 6-4 D6 R2M2 Description Reserved R2M2:R2M0 Must be left at 0. 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. Must be left at 0. D5 R2M1 D4 R2M0 D3 Reserved D2 R1M2 D1 R1M1 D0 R1M0 3 Reserved 15 www.national.com LM95231 2.0 LM95231 Registers Bits 2-0 Description 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 Value Temperature Data: LSb = 1˚C. Local Temperature LSB (Read Only Address 20h) 9-bit plus sign format: BIT Value Temperature Data: LSb = 0.25˚C. Remote Temperature MSB (Read Only Address 11h, 12h) 10 bit plus sign format: BIT Value D7 SIGN D6 64 D5 32 D4 16 D3 8 D2 4 D1 2 D0 1 D7 0.5 D6 0.25 D5 0 D4 0 D3 0 D2 0 D1 0 D0 0 D7 SIGN D6 64 D5 32 D4 16 D3 8 D2 4 D1 2 D0 1 Temperature Data: LSb = 1˚C. (Read Only Address 11h, 12h) 11-bit unsigned format: BIT Value D7 128 D6 64 D5 32 D4 16 D3 8 D2 4 D1 2 D0 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 Value D7 0.5 D6 0.25 D5 0.125 D4 0 D3 0 D2 0 D1 0 D0 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 Value D7 0.5 D6 0.25 D5 0.125 D4 0.0625 D3 0.03125 D2 0 D1 0 D0 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. www.national.com 16 LM95231 2.0 LM95231 Registers 2.7 MANUFACTURERS ID REGISTER (Continued) (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. 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: • • • • 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. (1) where: (5) 17 www.national.com LM95231 3.0 Applications Hints (Continued) 20120243 FIGURE 3. Thermal Diode Current Paths 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: 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. Processor Family Diode Equation ηD, non-ideality min Pentium III CPUID 67h Pentium III CPUID 68h/PGA370Socket/ Celeron Pentium 4, 423 pin Pentium 4, 478 pin Pentium 4 on 0.13 micron process, 2-3.06GHz Pentium 4 on 90 nm process Pentium M Processor (Centrino) MMBT3904 AMD Athlon MP model 6 AMD Athlon 64 AMD Opteron AMD Sempron 1.002 1.008 1.008 1 1.0057 typ 1.008 max 1.0125 1.0065 1.0125 Series R 0.9933 1.0045 1.0368 0.9933 1.0045 1.0368 1.0011 1.0021 1.0030 3.64 Ω 1.0083 1.011 1.023 3.33 Ω 1.00151 1.00220 1.00289 3.06 Ω 1.003 1.008 1.008 1.008 1.00261 1.016 1.096 1.096 0.93 Ω (6) www.national.com 18 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 LM95231 3.0 Applications Hints (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. 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 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. 3. 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. 1. 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. 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. • 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. 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 www.national.com 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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