LM95235CIMM

LM95235/LM95235Q Precision Remote Diode Temperature Sensor with SMBus Interface and TruTherm Technology August 15, 2008 LM95235/LM95235Q Precision Remote Diode Temperature Sensor with SMBus Interface and TruTherm™ Technology General Description The LM95235 is an 11-bit digital temperature sensor with a 2-wire System Management Bus (SMBus) interface and TruTherm technology that can monitor the temperature of a remote diode as well as its own temperature. The LM95235 can be used to very accurately monitor the temperature of external devices such as microprocessors, graphics processors, or a diode-connected MMBT3904 transistor. For automotive applications the LM95235Q is available that is AECQ100 Grade3 compliant and is manufactured on an Automotive Grade Flow. TruTherm BJT (transistor) beta compensation technology allows the LM95235 to precisely monitor thermal diodes found in 90 nm and smaller geometry processes. LM95235 reports temperature in two different formats for +127.875°C/-128°C range and 0°C/255°C range. The LM95235 T_CRIT and OS outputs are asserted when either unmasked channel exceeds its programmed limit and can be used to shutdown the system, to turn on the system fans, or as a microcontroller interrupt function. The current status of the T_CRIT and OS pins can be read back from the status registers via the SMBus interface. All limits have a shared programmable hysteresis register. The remote temperature channel of the LM95235 has a programmable digital filter. The LM95235 contains a diode model selection bit to select between a typical Intel® processor on a 65 nm or 90 nm process or MMBT3904, as well as an offset register for maximum flexibility and best accuracy. The LM95235 has a three-level address pin to connect up to 3 devices to the same SMBus master, that is shared with the OS output. The LM95235 has a programmable conversion rate register and a standby mode to save power. One conversion can be triggered in standby mode by writing to the one-shot register. ■ Diode Model Selection Bit - MMBT3904 or 65/90 nm ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ processor diodes Two Formats: −128°C to 127.875°C and 0°C to 255.875°C Digital filter for remote channel Programmable TCRIT and OS thresholds Programmable shared hysteresis register Diode Fault Detection Mask, Offset, and Status Registers SMBus 2.0 compatible interface, supports TIMEOUT Programmable conversion rate for best power consumption Three-level address pin Standby mode one-shot conversion control Pin-for-pin compatible with the LM86/LM89 8-pin MSOP package Key Specifications ■ Supply Voltage ■ Supply Current, Conv. Rate = 1 Hz ■ Remote Diode Temperature Accuracy  TA = 25°C to 85°C; TD = 60°C to 100°C  TA = 25°C to 85°C; TD = 40°C to 125°C ■ Local Temperature Accuracy  TA = 25°C to 100°C ■ Conversion Rate, Both Channels 3.0 V to 3.6 V 350 µA (typ) ±0.75°C (max) ±1.5°C (max) ±2.0°C (max) 16 to 0.4 Hz Applications ■ Processor/Computer System Thermal Management (e.g. Laptops, Desktops, Workstations, Servers) Electronic Test Equipment and Office Electronics ■ Features ■ Remote and Local temperature channels ■ TruTherm BJT beta compensation technology ■ LM95235Q is AEC-Q100 Grade 3 compliant and is manufactured on an Automotive Grade Flow Connection Diagram MSOP-8 20174902 TOP VIEW TruTherm™ is a trademark of National Semiconductor Corporation. Intel® is a registered trademark of Intel Corporation. Pentium® is a registered trademark of Intel Corporation. © 2008 National Semiconductor Corporation 201749 www.national.com LM95235/LM95235Q Ordering Information Order Code Packag e NS Package Markin Number g T36C T36C T36D T36D T36E T36E 36QE 36QE 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 Features LM95235CIMM LM95235CIMMX LM95235DIMM LM95235DIMMX LM95235EIMM LM95235EIMMX LM95235QEIMM LM95235QEIMMX 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 TA = 25°C to 85°C TA = -40°C to 85°C, TD = -40°C to 125°C TA = -40°C to 85°C, TD = -40°C to 125°C, 3904 only TA = -40°C to 85°C, TD = -40°C to 125°C, 3904 only AEC-Q100 Grade 3 Compiant with Automotive Grade Flow Simplified Block Diagram 20174901 www.national.com 2 LM95235/LM95235Q Pin Descriptions Pin Number 1 2 3 4 5 Name VDD D+ DT_CRIT GND Type Power Function and Connection Device power supply. Requires bypass capacitor of 10 µF in parallel with 0.1 µF and 100 pF. Place 100 pF closest to device pin. Analog Input/Output Positive input from the thermal diode. Analog Input/Output Negative input from the thermal diode. Digital Output Ground Critical temperature output. Open-drain output requires pull-up resistor. Active “LOW”. Device ground. Over-temperature shutdown comparator output or SMBus slave address input. Defaults as an SMBus slave address input that selects one of three addresses. Can be tied to VDD, GND, or to the middle of a resistor divider connected between VDD and GND. When programmed as an OS comparator output it is active “Low” and open drain. SMBus interface data pin. Open-drain output requires pull-up resistor. SMBus interface clock pin. 6 OS/A0 Digital Input/Output 7 8 SMBDAT SMBCLK Digital Input/Output Digital Input Typical Application 20174903 3 www.national.com LM95235/LM95235Q Absolute Maximum Ratings (Note 1) Supply Voltage, VDD Voltage at SMBDAT, SMBCLK,  T_CRIT, OS/A0 Pins Voltage at Other Pins Input Current at D− Pin (Note 4) Input Current at All Other Pins (Note 4) Output Sink Current SMBDAT, T_Crit, OS Pins Package Input Current (Note 4) ESD Susceptibility (Note 3) Human Body Model Machine Model Charged Device Model Junction Temperature (Note 2) Storage Temperature −0.3V to 6.0V −0.5V to 6.0V (VDD +0.3V) ±1 mA ±5 mA 10 mA 30 mA   2500V 250V 1000V +125°C −65°C to +150°C Operating Ratings (Note 1) Operating Temperature Range Electrical Characteristics Temperature Range LM95235CIMM LM95235DIMM LM95235EIMM, LM95235QEIMM Supply Voltage (VDD) -40°C to +125°C TMIN ≤ TA ≤ TMAX -40°C ≤ TA ≤ +85°C -40°C ≤ TA ≤ +85°C +3.0V to +3.6V 0°C ≤ TA ≤ +85°C Soldering process must comply with National Semiconductor's Reflow Temperature Profile specifications. Refer to www.national.com/packaging. (Note 5) Temperature-to-Digital Converter Characteristics Unless otherwise noted, these specifications apply for VDD = +3.0 Vdc to 3.6 Vdc. 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 LM95235. TA is the ambient temperature of the LM95235. TD is the junction temperature of the remote thermal diode. Parameter Conditions Typical (Note 6) LM95235 CIMM Limits (Note 7) LM95235 DIMM/ Limits (Note 7) LM95235 EIMM LM95235 QEIMM Limits (Note 7) ±2 ±6.0 ±0.75 ±1.0 Units Temperature Accuracy TA = 25°C to +100°C Using Local Diode (Note 8) T = -40°C to +25°C A Temperature Accuracy Using Remote Diode (Note 9) TA = +25°C to +85°C; TD = +60°C to +100°C TA = +25°C to +85°C; TD = +60°C to +100°C TA = +25°C to +85°C; TD = +40°C to +120°C TA = -40°C to +25°C; TD = +25°C to +125°C TA = -40°C to +25°C; TD = +25°C to +125°C TA = -40°C to +25°C; TD = -40°C to +25°C Remote Diode Measurement Resolution Local Diode Measurement Resolution Conversion Time, Fastest Setting (Note 10) Local and Remote Channels Local or Remote Channels Digital Filter Off Digital Filter On 65nm Intel Processor MMBT3904 MMBT3904 or 65nm Intel Processor MMBT3904 or 65nm Intel Processor MMBT3904 MMBT3904 ±1 ±2 ±2 ±6.0 °C (max) °C (max) °C (max) °C (max) ±0.5 ±0.5 ±0.75 ±1.0 ±0.75 ±1.0 ±0.75 ±1.5 ±1.5 ±1.5 °C (max) ±3.0 °C (max) ±3.0 ±5.0 11 0.125 13 0.03125 11 0.125 63 33 72 72 72 ±5.0 °C (max) °C (max) Bits °C Bits °C Bits °C ms (max) ms www.national.com 4 LM95235/LM95235Q Parameter Conditions Typical (Note 6) LM95235 CIMM Limits (Note 7) LM95235 DIMM/ Limits (Note 7) LM95235 EIMM LM95235 QEIMM Limits (Note 7) 650 Units Quiescent Current D− Source Voltage External Diode Current Source Diode Source Current Ratio Power-On Reset Voltage T_CRIT Pin Temperature Threshold OS Pin Temperature Threshold SMBus Inactive, 1 Hz conversion rate (Note 11) Standby Mode High-level Low-level 350 300 400 172 10.75 16 650 650 µA (max) µA mV 225 225 225 µA (max) µA 2.8 1.6 Default Default +110 +85 2.8 1.6 2.8 1.6 V (max) V (min) °C °C Logic Electrical Characteristics Digital DC Characteristics Unless otherwise noted, these specifications apply for VDD= +3.0 Vdc to 3.6 Vdc. Boldface limits apply for TA = TJ = TMIN to TMAX; all other limits TA= TJ= +25°C, unless otherwise noted. Symbol SMBDAT, SMBCLK INPUTS VIN(1) VIN(0) VIN(HYST) IIN(1) IIN(0) CIN A0 DIGITAL INPUT VIH VIM VIL IIN(1) IIN(0) CIN IOH VOL(T_CRIT, OS) VOL(SMBDAT) COUT Input High Voltage Input Middle Voltage Input Low Voltage Logical “1” Input Current Logical “0” Input Current Input Capacitance High Level Output Leakage Current T_CRIT, OS Low Level Output Voltage SMBDAT Low Level Output Voltage Digital Output Capacitance VOUT = VDD IOL = 6 mA IOL = 4 mA IOL = 6 mA 5 VIN = VDD VIN = 0 V −0.005 0.005 5 10 0.4 0.4 0.6 0.90 × VDD 0.57 × VDD 0.43 × VDD 0.10 × VDD −10 +10 V (min) V (max) V (min) V (max) µA (max) µA (max) pF µA (max) V (max) V (max) V (max) pF Logical “1” Input Voltage Logical “0” Input Voltage SMBDAT and SMBCLK Digital Input Hysteresis Logical “1” Input Current Logical “0” Input Current Input Capacitance VIN = VDD VIN = 0 V 400 −0.005 0.005 5 −10 +10 2.1 0.8 V (min) V (max) mV µA (max) µA (max) pF Parameter Conditions Typical (Note 6) Limits (Note 7) Units (Limit) SMBDAT, T_CRIT, OS DIGITAL OUTPUTS 5 www.national.com LM95235/LM95235Q 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 LM95235 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 LM95235. They adhere to, but are not necessarily, the SMBus specifications. Symbol Parameter Conditions Typical Limits (Note 6) (Note 7) 100 10 4.7 25 4.0 1 0.3 250 25 35 250 300 1075 100 100 0.6 1.3 Units (Limit) kHz (max) kHz (min) µs (min) ms (max) µs (min) µs (max) µs (max) ns (max) ms (min) ms (max) ns (min) ns (min) ns (max) ns (min) ns (min) µs (min) µs (min) fSMB tLOW tHIGH tR,SMB tF,SMB tOF tTIMEOUT tSU;DAT tHD;DAT tHD;STA tSU;STO tSU;STA tBUF SMBus Clock Frequency SMBus Clock Low Time SMBus Clock High Time SMBus Rise Time SMBus Fall Time Output Fall Time SMBDAT and SMBCLK Time Low for Reset of Serial Interface (Note 14) Data In Setup Time to SMBCLK High 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 from VIN(0)max to VIN(0)max from VIN(1)min to VIN(1)min (Note 12) (Note 13) CL = 400 pF, IO = 3 mA, (Note 13) SMBus Communication 20174909 www.national.com 6 LM95235/LM95235Q Notes 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: Thermal resistance junction-to-ambient when attached to a printed circuit board with 1 oz. foil and no airflow is:   θJA for MSOP-8 package = 210°C/W Note 3: Human body model (HBM) is a charged 100 pF capacitor discharged into a 1.5 kΩ resistor. Machine model (MM), is a charged 200 pF capacitor 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 4: 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 LM95235's pins. Care should be taken not to forward bias the parasitic diodes on pins 2 and 3. Doing so by more than 50 mV may corrupt the temperature measurements. SNP refers to Snap-back device. Pin # 1 2 3 4 5 6 7 8 Label VDD D+ D− T_CRIT GND OS/A0 SMBDAT SMBCLK Circuit A A A B A B B B            Circuit A 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 LM95235 and the thermal resistance. See (Note 2) for the thermal resistance to be used in the self-heating calculation. Note 9: The accuracy of the LM95235 is guaranteed when using a typical thermal diode of an Intel processor on a 65 nm process or an MMBT3904 diodeconnected 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: This specification is provided only to indicate how often temperature data is updated. The LM95235 can be read at any time without regard to conversion state (and will yield last conversion result). Note 11: Quiescent current will not increase substantially when the SMBus is active. 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(0)max - 0.15V). Note 14: Holding the SMBDAT and/or SMBCLK lines Low for a time interval greater than tTIMEOUT will reset the LM95235's SMBus state machine, therefore setting SMBDAT and SMBCLK pins to a high impedance state.            Circuit B Pin ESD Protection Structure Circuits 7 www.national.com LM95235/LM95235Q Typical Performance Characteristics Thermal Diode Capacitor or PCB Leakage Current Effect Remote Diode Temperature Reading Remote Temperature Reading Sensitivity to Thermal Diode Filter Capacitance, TruTherm Enabled 20174905 20174907 Conversion Rate Effect on Average Power Supply Current Intel Processor on 65nm Process or 90nm Process Thermal Diode Performance Comparison 20174906 20174950 www.national.com 8 LM95235/LM95235Q 1.0 Functional Description The LM95235 is a temperature sensor that measures Local and Remote temperature zones. The LM95235 uses a ΔVbe temperature sensing method. A differential voltage, representing temperature, is digitized using a Sigma-Delta analog to digital converter. TruTherm Technology allows the LM95235 to accurately sense the temperature of a thermal diode found on die fabricated using a sub-micron process. For more information on TruTherm Technology see Section 3.0 Application Hints. The LM95235 is compatible with the serial SMBus version 2.0 two-wire serial interface. The LM95235 has OS and TCRIT open-drain digital outputs that indicate the state of the local and remote temperature readings when compared to user-programmable limits. If enabled, the local temperature is compared to the user-programmable Local Shared OS and TCRIT Limit Register (Default Value = 85°C). The comparison result can trigger the T_CRIT pin and/or the OS pin depending on the settings of the Local TCRIT Mask and OS Mask bits found in Configuration Register 1. The comparison result can also be read back from Status Register 1. If enabled, the remote temperature is compared to the user-programmable Remote TCRIT Limit Register (Default Value = 110°C), and the Remote OS Limit Register (Default Value = 85°C) values. The comparison result can trigger the T_CRIT pin and/or the OS pin depending on the settings of Configuration Register 1. The following table describes the default temperature settings for each measured temperature that triggers T_CRIT and/or OS pins: Output Pin T_CRIT OS Remote, °C 110 85 Local, °C 85 85 LM95235 Register table. The lower 2-bits of the remote temperature reading will contain temperature information only if the digital filter is enabled. If the digital filter is disabled, these two bits will read back 0. The signed and unsigned remote temperature readings are available simultaneously in separate registers, therefore allowing both negative temperatures and temperatures 128°C and above to be measured. All Limit Registers support unsigned temperature format with 1°C LSb resolution. The Local Shared TCRIT and OS Limit Register is 7 bits for limits between 0°C and 127°C. The Remote Temperature TCRIT and OS Limit Registers are 8 bits each for limits between 0°C and 255°C. 1.1 CONVERSION SEQUENCE In the power-up default state the LM95235 takes a maximum of 1 second to convert the Local Temperature, Remote Temperature, and to update all of its registers. Only during the conversion process is the Busy bit (D7) in Status Register 1 (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 Conversion Rate Register (R/ W: 04h/0Ah). When the conversion rate is modified a delay is inserted between conversions, the actual maximum conversion time remains at 72 ms. Different conversion rates will cause the LM95235 to draw different amounts of supply current as shown in Figure 1. The following table describes the limit register mapping to the T_CRIT and/or OS pins: Output Pin T_CRIT OS Remote Remote TCRIT Limit Remote OS Limit Local Local Shared OS/TCRIT Limit Local Shared OS/TCRIT Limit The T_CRIT and OS outputs are open-drain, active low. The remote temperature readings support a programmable digital filter. Based on the settings in Configuration Register 2 a digital filter can be turned on to improve the noise performance of the remote temperature as well as to increase the resolution of the temperature reading. If the filter is enabled the filtered readings are used for TCRIT and OS comparisons. The LM95235 may be placed in low power consumption (Standby) mode by setting the STOP/RUN bit found in Configuration Register 1. In the Standby mode, the LM95235’s SMBus interface remains active while all circuitry not required is turned off. In the Standby mode the host can trigger one round of conversions by writing to the One-Shot Register. The value written into this register is not kept. Local and Remote temperatures will be converted once and the T_CRIT and OS pins will reflect the comparison results based on this set of conversions results. All the temperature readings are in 16-bit left-justified word format. The 10-bit plus sign local temperature reading is contained in two 8-bit registers: Local Temp MSB and Local Temp LSB Registers. The remote temperature supports both a 13bit unsigned and a 12-bit plus sign format. These readings are available in their corresponding registers as described in the 20174906 FIGURE 1. Conversion Rate Effect on Power Supply Current 1.2 POWER-ON-DEFAULT STATES LM95235 always powers up to these known default states. The LM95235 remains in these states until after the first conversion. 1. Command Register set to 00h 2. Conversion Rate register defaults to 02h (1 second). 3. Local Temperature set to 0°C until the end of the first conversion 4. Remote Diode Temperature set to 0°C until the end of the first conversion 5. Remote OS limit default is 55h (85 °C). 6. Local Shared and TCRIT limit default is 55h (85 °C). 7. Remote TCRIT limit default is 6Eh (110 °C). 8. Remote Offset High and Low bytes default to 00h. 9 www.national.com LM95235/LM95235Q 9. Configuration Register 1 defaults to 00h. This sets the LM95235 as follows: A. Figure 2 depicts the filter output in response to a step input and an impulse input. The STOP/RUN defaults to the active/converting mode. B. The Local and Remote TCRIT and OS Masks are reset to 0. 10. Configuration Register 2 defaults to 1Fh. This sets the LM95235 as follows: A. B. C. D. E. Remote Diode digital filter defaults on. The Remote Diode mode defaults to a typical Intel processor on 65/90 nm process. Diode Fault Mask bit for TCRIT defaults to 1. Diode Fault Mask bit for OS defaults to 0. Pin 6 Function defaults to Address Input function (A0). 20174925 a) Seventeen and fifty degree step response 1.3 SMBus INTERFACE The LM95235 operates as a slave on the SMBus, so the SMBCLK line is an input and the SMBDAT line is bidirectional. The LM95235 never drives the SMBCLK line and it does not support clock stretching. According to SMBus specifications, the LM95235 has a 7-bit slave address. Three SMBus addresses can be selected by connecting pin 6 (A0) to either Low, Mid-Supply or High voltages. The address selection table below shows the possible selections. State of the A0 Pin Low Mid-Supply High SMBus Device Address HEX 18 29 4C Binary 001 1000 010 1001 100 1100 20174926 The OS/A0 pin, after power-up, defaults as an address select input pin (A0). After power-up, the OS/A0 pin can only be programmed as an OS output when it is in the “High” state. Therefore, 4Ch is the only valid slave address that can be used when the OS/A0 pin is programmed to function as an OS output. When the OS/A0 pin is programmed to function as an A0 input the LM95235 will immediately detect the state of this pin to determine its SMBus slave address. The LM95235 does not latch the state of the A0 pin when it is functioning as an input. 1.4 DIGITAL FILTER In order to suppress erroneous remote temperature readings due to noise, the LM95235 incorporates a digital filter for the Remote Temperature Channel. The filter is accessed in the Configuration Register 2, bits D2 (FE1) and D1(FE0). The filter can be set according to the following table. FE1 0 0 1 1 FE0 0 1 0 1 Filter Setting Filter Off Reserved Reserved Filter On b) Impulse response with input transients less than 4°C 20174928 c) Impuse response with input transients greater than 4° C FIGURE 2. Filter Impulse and Step Response Curves Figure 3 shows the filter in use in a typical Intel processor on a 65/90 nm process system. Note that the two curves have been purposely offset for clarity. Inserting the filter does not induce an offset as shown. www.national.com 10 LM95235/LM95235Q 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 20174927 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 13-bit, unsigned binary Hex 7D00h 1900h 0100h 0008h 0000h FFF8h FF00h E700h C900h −55°C FIGURE 3. Digital Filter Response in a typical Intel processor on a 65 nm or 90 nm process. The filter curves were purposely offset for clarity. 1.5 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 10-bit plus sign, two's complement word and 11bit 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 report "0". Remote temperature data with the digital filter on is represented by a 12-bit plus sign, two's complement word and 13bit 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 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 Hex FFE0h FF00h C900h 7D00h 1900h 0100h 0020h 0000h Hex 7D00h 1900h 0100h 0020h 0000h FFE0h FF00h E700h C900h Temperature +255.875°C +255°C +201°C +125°C +25°C +1°C +0.03125°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 0000 1000 0000 0000 0000 0000 Hex FFE0h FF00h C900h 7D00h 1900h 0100h 0008h 0000h Local Temperature data is represented by a 10-bit plus sign, two's complement 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". Local temperature readings greater than +127.875°C are clamped to +127.875°C, they will not roll-over to negative temperature readings. 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 Hex 7D00h 1900h 0100h 0020h 0000h FFE0h FF00h E700h C900h 1.6 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 LM95235. The maximum resistance of the pull-up to provide a 2.1V high level, based on LM95235 specification for High 11 www.national.com LM95235/LM95235Q Level Output Current with the supply voltage at 3.0V, is 82 kΩ (5%) or 88.7 kΩ (1%). 1.7 T_CRIT OUTPUT AND TCRIT LIMIT The LM95235's T_CRIT pin is an active-low open-drain output that is triggered when the local and/or the remote temperature conversion is above the limits defined by the Remote and/or Local Limit registers. The state of the T_CRIT pin will return to the HIGH state when both the Local and Remote temperatures are below the values programmed into the Limit Registers less the value in the Common Hysteresis Register. Additionally, if the remote temperature exceeds the value in the Remote TCRIT Limit Register the Status Bit for Remote TCRIT (RTCRIT), in Status Register 1, is set to 1. In the same way if the local temperature exceeds the value in the Local Shared OS and TCRIT Limit Register the Status Bit for the Shared Local OS and TCRIT (LOC) bit in Status Register 1 is set to 1.The T_CRIT output and the Status Register flags are updated after every Local and Remote temperature conversion. See Figure 4 20174915 FIGURE 5. OS Temperature Response Diagram 1.9 DIODE FAULT DETECTION The LM95235 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 °C if unsigned format is selected. In addition, the Status Register 1 bit D2 is set. 1.10 COMMUNICATING with the LM95235 The data registers in the LM95235 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 LM95235 falls into one of four types of user accessibility: 1. Read only 2. Write only 3. Write/Read same address 4. Write/Read different address A Write to the LM95235 will always include the address byte and the command byte. A write to any register requires one data byte. Reading the LM95235 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 LM95235), 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 LM95235 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 lockedin. 20174913 FIGURE 4. T_CRIT Comparator Temperature Response Diagram 1.8 OS OUTPUT AND OS LIMIT The LM95235's OS/A0 pin is selected as an OS digital output as described in Section 1.3. As an OS pin, it is activated whenever the local and/or remote temperature conversion is above the limits defined by the Limit registers. If the remote temperature exceeds the value in the Remote OS Limit Register the Status Bit for Remote OS (ROS) in Status Register 1 is set to 1. In the same way if the local temperature exceeds the value in the Local Shared OS and TCRIT Limit Register the Status Bit for the Shared Local OS and TCRIT (LOC) bit in Status Register 1 is set to 1. The state of the T_CRIT pin output will return to the HIGH state when both the Local and Remote temperatures are below the values programmed into the Limit Registers less the value in the Common Hysteresis Register. The OS output and the Status Register flags are updated after every Local and Remote temperature conversion. See Figure 5. www.national.com 12 LM95235/LM95235Q 20174911 (a) Serial Bus Write to the Internal Command Register 20174910 (b) Serial Bus Write to the internal Command Register followed by a Data Byte 20174912 (c) Serial Bus byte Read from a Register with the internal Command Register preset to desired value. 20174914 (d) Serial Bus Write followed by a Repeat Start and Immediate Read FIGURE 6. SMBus Timing Diagrams for Access of Data (Default Address of 4Ch is shown) 13 www.national.com LM95235/LM95235Q 1.11 SERIAL INTERFACE RESET In the event that the SMBus Master is RESET while the LM95235 is transmitting on the SMBDAT line, the LM95235 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 LM95235 SMBus state machine resets to the SMBus idle state if either SMBDAT or SMBCLK are held low for more than 35 ms (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 - 35 ms. Therefore, to insure a timeout of all devices on the bus the SMBCLK or SMBDAT lines must be held low for at least 35 ms. 2. When SMBDAT is HIGH, have the master initiate an SMBus start. The LM95235 will respond properly to an SMBus start condition at any point during the communication. After the start the LM95235 will expect an SMBus Address address byte. 1.12 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. www.national.com 14 LM95235/LM95235Q 2.0 LM95235 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. POR means Power-On Reset. P0-P7: Command P7 P6 P5 P4 P3 P2 P1 P0 Command Register Summary Read Write Address Address (Hex) (Hex) 0x00 0x30 0x01 0x10 NA NA NA NA No. of bits 8 3 8 5/3 POR Read/ Default Write (Hex) − − − − RO RO RO RO Register Name Description TEMPERATURE SIGNED VALUE REGISTERS Local Temp MSB Local Temp LSB Remote Temp MSB – Signed Remote Temp LSB – Signed Remote Temp MSB – Unsigned Remote Temp LSB – Unsigned Supports SMBus byte All unused bits are reported as "0". Supports SMBus byte All unused bits are reported as "0". TEMPERATURE UNSIGNED VALUE REGISTERS 0x31 0x32 NA NA 8 5/3 − − RO RO Supports SMBus byte reads All unused bits are reported as "0". DIODE CONFIGURATION REGISTERS Configuration Register 2 Remote Offset High Byte Remote Offset Low Byte 0xBF 0x11 0x12 0xBF 0x11 0x12 5 8 3 0x1F 0x00 0x00 R/W R/W R/W Filter Enable, Diode Model Select, Diode Fault Mask; Pin 6 OS/A0 function select 2's Complement 2's Complement All unused bits are reported as "0". STOP/RUN , Remote TCRIT mask, Remote OS mask, Local TCRIT mask, Local OS mask Continuous or specific settings A write to this register activates one conversion if STOP/RUN bit = 1. Busy bit, and status bits Not Ready bit, Diode detect bit Unsigned 0 to 255 °C Default 85 °C Unsigned 0 to 127 °C Default 85 °C Unsigned 0 to 255 °C Default 110 °C up to 31°C GENERAL CONFIGURATION REGISTERS Configuration Register 1 0x03/ 0x09 0x09/ 0x03 5 0x00 R/W Conversion Rate One-Shot STATUS REGISTERS Status Register 1 Status Register 2 LIMIT REGISTERS Remote OS Limit Local Shared OS and T_Crit Limit Remote T_Crit Limit Common Hysteresis 0x04/0x0 0x04/0x0 A A NA 0x0F 2 − 0x02 − R/W WO 0x02 0x33 0x07/ 0x0D 0x20 0x19 0x21 NA NA 0x0D/ 0x07 0x20 0x19 0x21 5 2 − − RO RO 8 7 8 5 0x55 0x55 0x6E 0x0A R/W R/W R/W R/W 15 www.national.com LM95235/LM95235Q Register Name Read Write Address Address (Hex) (Hex) 0xFE 0xFF No. of bits POR Read/ Default Write (Hex) 0x01 0xB1 RO RO Description IDENTIFICATION REGISTERS Manufacturer ID Revision ID Always returns 0x01 Returns revision number. www.national.com 16 LM95235/LM95235Q 2.1 LOCAL and REMOTE MSB and LSB TEMPERATURE REGISTERS Local Temperature MSB (Read Only Address 00h) 10-bit plus sign format: BIT Value Temperature Data: LSb = 1°C. Local Temperature LSB (Read Only Address 30h) 10-bit plus sign format: BIT Value Temperature Data: LSb = 0.125°C. Signed Remote Temperature MSB (Read Only Address 01h) 12-bit plus sign format: BIT Value Temperature Data: LSb = 1°C. Signed Remote Temperature LSB, Filter On (Read Only Address 10h) 12-bit plus sign 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 D7 SIGN D6 64 D5 32 D4 16 D3 8 D2 4 D1 2 D0 1 D7 0.5 D6 0.25 D5 0.125 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 Signed Remote Temperature LSB, Filter Off (Read Only Address 10h) 12-bit plus sign 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 filter off or 0.03125°C filter on. Unsigned Remote Temperature MSB (Read Only Address 31h) 13-bit unsigned format: BIT Value Temperature Data: LSb = 1°C. Unsigned Remote Temperature LSB, Filter On (Read Only Address 32h) 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 D7 128 D6 64 D5 32 D4 16 D3 8 D2 4 D1 2 D0 1 17 www.national.com LM95235/LM95235Q Unsigned Remote Temperature LSB, Filter Off (Read Only Address 32h) 13-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 filter off or 0.03125°C filter on. 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 lockedin. 2.2 DIODE CONFIGURATION REGISTERS Configuration Register 2 (Read/write Address BFh): D7 0 D6 OS/A0 Function Select D5 OS Fault Mask D4 T_CRIT Mask D3 TruTherm Select D2 RFE1 D1 RFE0 D0 1 Bits 7 6 5 4 Name Reserved OS/A0 Function Select Diode Fault Mask for OS Diode Fault Mask for T_CRIT Description Reports "0" when read. 0: Address (A0) function is enabled 1: Over-temperature Shutdown (OS) is enabled 0: Off 1: On 0: Off 1: On 0: Selects Diode Model 2, MMBT3904, with TruTherm technology disabled. 1: Selects Diode Model 1, A typical Intel Processor, with 65 nm or 90 nm technology, and TruTherm technology enabled. 00: Filter Disable 01: Reserved 10: Reserved 11: Filter Enable Reports "1" when read. 3 Remote Diode TruTherm Mode Select 2-1 Remote Filter Enable 0 Reserved Power up default is 1Fh. Remote Offset High Byte (2's Complement) (R/W Address 11h) 10-bit plus sign format: BIT Value Power up default is 00h. Remote Offset Low Byte (2's Complement) (R/W Address 12h) 10-bit plus sign format: BIT Value D7 0.50 D6 0.25 D5 0.125 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 Power up default is 00h. LSb = 0.125 °C. www.national.com 18 LM95235/LM95235Q 2.3 GENERAL CONFIGURATION REGISTERS Configuration Register 1 (Read/write Address 03h/09h or 09h/03h): D7 0 D6 STOP/RUN D5 0 D4 Remote T_CRIT Mask Bits 7 6 5 4 3 2 1 0 Power up default is 00h. Conversion Rate Register (Read/write Address 04h/0Ah or 0Ah/04h):2-bit format: BIT Value Bits 7:2 D7 0 D6 0 Name Reserved D5 0 D4 0 D3 0 D2 0 D1 MSb D0 LSb Name Reserved STOP/RUN Reserved Remote T_CRIT Mask Remote OS Mask Local T_CRIT Mask Local OS Mask Reserved D3 D2 D1 Local OS Mask D0 0 Remote OS Mask Local T_CRIT Mask Description Reports "0" when read. 0: Active / Converting 1: Standby Reports "0" when read. 0: Off 1: On 0: Off 1: On 0: Off 1: On 0: Off 1: On Reports "0" when read. Description Reports "0" when read. 1:0 00: Continuous (33 ms typical when remote diode is missing or fault or 63 ms typical with remote diode connected) Conversion Rate 01: 0.364 seconds 10: 1 second 11: 2.5 seconds Power up default is 02h (1 second). One Shot Register (Write Only Address 0Fh): Writing to this register will start one conversion if the device is in standby mode (i.e. STOP/RUN bit = 1). 19 www.national.com LM95235/LM95235Q 2.4 STATUS REGISTERS Status Register 1 (Read Only Address 02h): D7 Busy Bits 7 6-5 4 3 2 Diode Fault Busy Reserved ROS Reserved D6 0 Name Report "0" when read. Status Bit for Remote OS Reports "0" when read. Status bit for missing diode (Either D+ is shorted to GND, and/or VDD, and/or D-; or D+ is floating.) Note: The unsigned registers will report 0°C if read; the signed value registers will report −128.000°C. Status bit for Remote TCRIT. Status bit for the shared Local OS and TCRIT . Status Register 2 (Read Only Address 33h): D7 Not Ready Bits 7 6 5-0 Name Not Ready TruTherm 3904 Detect Reserved D6 TruTherm 3904 Detect D5 0 D4 0 D3 0 Description Waiting for 30 ms power-up sequence to end. 1: MMBT3904 is connected and TruTherm technology is enabled. 0: MMBT3904 is connected and TruTherm technology is disabled. Reports "0" when read. D2 0 D1 0 D0 0 D5 0 D4 ROS D3 0 D2 Diode Fault Description When set to "1" the part is converting. D1 RTCRIT D0 LOC 1 0 RTCRIT LOC 2.5 LIMIT REGISTERS Unsigned Remote OS Limit - 0°C to 255°C (Read/Write Address 07h/0Dh or 0Dh/07h): D7 128 D6 64 D5 32 D4 16 D3 8 D2 4 D1 2 D0 1 Power on Reset default is 55h (85°C). Unsigned Local Shared OS and T_CRIT Limit - 0°C to 127°C (Read/Write Address 20h): D7 128 D6 64 D5 32 D4 16 D3 8 D2 4 D1 2 D0 1 Power on Reset default is 55h (85°C). Unsigned Remote T_CRIT Limit - 0°C to 255°C (Read/Write Address 19h): D7 128 D6 64 D5 32 D4 16 D3 8 D2 4 D1 2 D0 1 Power on Reset default is 6Eh (110°C). www.national.com 20 LM95235/LM95235Q Common Hysteresis Register (Read/Write Address 21h): D7 0 D6 0 D5 0 D4 16 D3 8 D2 4 D1 2 D0 1 Power on Reset default is 0Ah (10°C). 2.6 IDENTIFICATION REGISTERS Manufacturers ID Register (Read Only Address FEh): Always returns 01h. D7 0 D6 0 D5 0 D4 0 D3 0 D2 0 D1 0 D0 1 Revision ID Register (Read Only Address FFh): Default is B1h. This register will increment by 1 every time there is a revision to the die by National Semiconductor. The initial revision bits for B1h are shown below. D7 1 D6 0 D5 1 D4 1 D3 0 D2 0 D1 0 D0 1 21 www.national.com LM95235/LM95235Q 3.0 Applications Hints The LM95235 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 LM95235'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 LM95235 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 LM95235'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 LM95235'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 LM95235's TruTherm technology allows accurate sensing of integrated thermal diodes, such as those found on most processors. With TruTherm technology turned off, the LM95235 can measure a diode-connected transistor such as the MMBT3904 or the thermal diode found in an AMD processor. The LM95235 has been optimized to measure the remote thermal diode integrated in a typical Intel processor on 65 nm or 90 nm process or an MMBT3904 transistor. Using the Remote Diode Model Select register either pair of remote inputs can be assigned to be either a typical Intel processor on 65 nm or 90 nm 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 = 1.6×10−19 Coulombs (the electron charge), T = Absolute Temperature in Kelvin k = 1.38×10−23 joules/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 7 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) www.national.com 22 LM95235/LM95235Q 20174943 FIGURE 7. Thermal Diode Current Paths TruTherm should only be enabled when measuring the temperature of a transistor integrated as shown in the processor of Figure 7, because Equation 5 only applies to this topology. 3.1.2 Calculating Total System Accuracy The voltage seen by the LM95235 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 ΔVBE is proportional to both η and T, the variations in η cannot be distinguished from variations in temperature. Since the nonideality factor is not controlled by the temperature sensor, it will directly add to the inaccuracy of the sensor. For the for Intel processor on 65nm process, Intel specifies a +4.06%/ −0.897% 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 ±1.0°C at a temperature of 80°C (353 Kelvin) and the processor diode has a nonideality variation of +1.19%/−0.27%. The resulting system accuracy of the processor temperature being sensed will be: TACC = + 1.0°C + (+4.06% of 353 K) = +15.3 °C and TACC = - 1.0°C + (−0.89% of 353 K) = −4.1 °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 ±0.39% for the Pentium 4 processor on 90 nm process. The resulting accuracy when using TruTherm technology improves to: TACC = ±0.75°C + (±0.39% of 353 K) = ± 2.16 °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 Intel processors in 65 nm process, this is specified at 4.52Ω typical. The LM95235 accommodates the typical series resistance of Intel Processor on 65 nm process. The error that is not accounted for is the spread of the processor'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 LM95235 is simply: (6) 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 LM95235. Processor Family Transistor Equation ηT, non-ideality min Intel Processor on 65 nm process Processor Family 0.997 typ 1.001 max 1.005 4.52 Series R,Ω Diode Equation ηD, nonideality min typ 1.0065 max 1.0125 Series R,Ω 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 3.06 GHz 1 1.0057 1.008 1.0125 0.9933 0.9933 1.0011 1.0045 1.0045 1.0021 1.0368 1.0368 1.0030 3.64 Pentium 4 on 90 nm 1.0083 process Intel Processor on 65 nm process 23 1.011 1.009 1.023 1.050 3.33 4.52 1.000 www.national.com LM95235/LM95235Q Pentium M (Centrino) MMBT3904 AMD Athlon MP model 6 AMD Athlon 64 AMD Opteron AMD Sempron 1.00151 1.00220 1.003 1.00289 3.06 3.2 PCB LAYOUT FOR MINIMIZING NOISE 1.002 1.008 1.008 1.008 1.008 1.008 1.00261 1.016 1.096 1.096 0.93 20174917 3.1.3 Compensating for Different Non-Ideality In order to compensate for the errors introduced by non-ideality, 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 LM95235 is calibrated for two non-ideality factors and series resistance values thus supporting the MMBT3904 transistor and Intel processors on 65nm process without the requirement for additional trims. For most accurate measurements TruTherm mode should be turned on when measuring the Intel processor on 65nm process to minimize the error introduced by the false non-ideality spread (see 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 LM95235. FIGURE 8. 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 LM95235 can cause temperature conversion errors. Keep in mind that the signal level the LM95235 is trying to measure is in microvolts. The following guidelines should be followed: 1. 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. A bulk capacitance of approximately 10 µF needs to be in the near vicinity of the LM95235. 2. A 100 pF diode bypass capacitor is recommended to filter high frequency noise but may not be necessary. Make sure the traces to the 100 pF capacitor are matched. Place the filter capacitors close to the LM95235 pins. 3. Ideally, the LM95235 should be placed within 10 cm of the Processor diode pins with the traces being as straight, short and identical as possible. Trace resistance of 1Ω can cause as much as 0.62°C of error. This error can be compensated by using simple software offset compensation. 4. Diode traces should be surrounded by a GND guard ring to either side, above and below if possible. This GND guard should not be between the D+ and D− lines. In the event that noise does couple to the diode lines it would be ideal if it is coupled common mode. That is equally to the D+ and D− lines. 5. Avoid routing diode traces in close proximity to power supply switching or filtering inductors. 6. Avoid running diode traces close to or parallel to high speed digital and bus lines. Diode traces should be kept at least 2 cm 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 LM95235'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 400 mVp-p (typical hysteresis) and undershoot less than 500 mV below GND, may prevent successful SMBus communication with the LM95235. SMBus no acknowledge is the most common symptom, causing unnecessary traffic on the bus. Although 24 (7) where • ηS = LM95235 non-ideality for accuracy specification • ηPROCESSOR = Processor thermal diode typical non-ideality • TCR = center of the temperature range of interest in °C The correction factor should be directly added to the temperature reading produced by the LM95235. For example when using the LM95235, 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: (8) Therefore, 1.75°C should be subtracted from the temperature readings of the LM95235 to compensate for the differing typical non-ideality target. www.national.com LM95235/LM95235Q the SMBus maximum frequency of communication is rather low (100 kHz 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 3 dB corner frequency of about 40 MHz is included on the LM95235'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. 25 www.national.com LM95235/LM95235Q Physical Dimensions inches (millimeters) unless otherwise noted 8-Lead Molded Mini-Small-Outline Package (MSOP), JEDEC Registration Number MO-187 Order Number LM95235CIMM, LM95235DIMM, LM95235EIMM, LM95235QEIMM, LM95235CIMMX, LM95235DIMMX, LM95235EIMMX, and LM95235QEIMMX, NS Package Number MUA08A www.national.com 26 LM95235/LM95235Q Notes 27 www.national.com LM95235/LM95235Q Precision Remote Diode Temperature Sensor with SMBus Interface and TruTherm Technology Notes For more National Semiconductor product information and proven design tools, visit the following Web sites at: Products Amplifiers Audio Clock Conditioners Data Converters Displays Ethernet Interface LVDS Power Management Switching Regulators LDOs LED Lighting PowerWise Serial Digital Interface (SDI) Temperature Sensors Wireless (PLL/VCO) www.national.com/amplifiers www.national.com/audio www.national.com/timing www.national.com/adc www.national.com/displays www.national.com/ethernet www.national.com/interface www.national.com/lvds www.national.com/power www.national.com/switchers www.national.com/ldo www.national.com/led www.national.com/powerwise www.national.com/sdi www.national.com/tempsensors www.national.com/wireless WEBENCH Analog University App Notes Distributors Green Compliance Packaging Design Support www.national.com/webench www.national.com/AU www.national.com/appnotes www.national.com/contacts www.national.com/quality/green www.national.com/packaging www.national.com/quality www.national.com/refdesigns www.national.com/feedback Quality and Reliability Reference Designs Feedback THE CONTENTS OF THIS DOCUMENT ARE PROVIDED IN CONNECTION WITH NATIONAL SEMICONDUCTOR CORPORATION (“NATIONAL”) PRODUCTS. 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