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Precision Remote Diode Digital Temperature Sensor: LM95245


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Precision Remote Diode Digital Temperature Sensor: LM95245

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Precision Remote Diode Digital Temperature Sensor: LM95245

  1. 1. Precision Remote Diode Digital Temperature Sensor: LM95245 <ul><li>Source: National Semiconductor </li></ul>
  2. 2. Introduction <ul><li>Purpose </li></ul><ul><ul><li>Precision Remote Diode Digital Temperature Sensor: LM95245 </li></ul></ul><ul><li>Outline </li></ul><ul><ul><li>Features and Application </li></ul></ul><ul><ul><li>Working principle of Digital sensor </li></ul></ul><ul><ul><li>Simplified block diagram </li></ul></ul><ul><ul><li>SMBus interface and performance characteristic </li></ul></ul><ul><li>Content </li></ul><ul><ul><li>15 pages </li></ul></ul>
  3. 3. Features ■ Remote and Local temperature channels ■ Targeted for Intel 45nm 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 ■ 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 LM95235 and LM86/LM89/ LM99 ■ 8-pin MSOP and SOP packages
  4. 4. Applications <ul><li>■ Processor/Computer System Thermal Management </li></ul><ul><li>(e.g. Laptops, Desktops, Workstations, Servers) </li></ul><ul><li>■ Electronic Test Equipment </li></ul><ul><li>■ Office Electronics </li></ul>
  5. 5. Introducing TruTherm™ Technology <ul><li>TruTherm stands for “True Thermal Measurement” and is the brand name for National’s new temperature monitoring technology </li></ul><ul><li>TruTherm ™ technology is an improved method of measuring temperature on integrated circuits designed in sub-micron (90nm & below) processes </li></ul><ul><li>Complex integrated circuits such as microprocessors, graphics processors and FPGA’s are being designed in smaller sub-micron geometries to reach higher speeds & integration </li></ul><ul><li>Internal thermal diodes connect to external temperature sensors to accurately monitor temperature, but in sub-micron geometries, readings based on these diodes vary greatly from processor to processor </li></ul><ul><li>Traditional approaches to accurately monitor the thermal diodes are no longer sufficient to achieve high-accuracy targets </li></ul>
  6. 6. Remote-Diode Temperature Sensing <ul><li>RDTS circuitry by concluding that the collector-current ratio will match the emitter-current ratio in all cases. </li></ul><ul><li>RDTS no longer holds true for sub-micron geometry processes measurement. </li></ul><ul><li>TruTherm BJT/Transistor beta compensation technology should only be enabled to measure. </li></ul>
  7. 7. Working Principle of LM95245 <ul><li>The series resistance on D+ and D− contributes to temperature error </li></ul><ul><li>The amount of temperature offset will depend on the magnitude of the difference between the two non-ideality factors. </li></ul><ul><li>It has an 11-bit temperature resolution and thermal sensor is capable of providing a digital output with a step size of 0.125 °C. </li></ul>
  8. 8. LM95245 Best Accuracy <ul><li>Previous Temperature Measurement Technologies </li></ul><ul><ul><li>Inaccurate results with 45 nm processors </li></ul></ul><ul><ul><li>Temperature Error varies from 5°C to 30°C </li></ul></ul><ul><ul><li>Spread between two processors is over 5°C </li></ul></ul><ul><ul><li>Noisy Output </li></ul></ul><ul><li>LM95245 TruTherm Measurement </li></ul><ul><ul><li>TruTherm™ technology for beta compensation and more </li></ul></ul><ul><ul><li>Temperature Error less than 3°C up to 125°C </li></ul></ul><ul><ul><li>Spread between two processors is less than 0.9°C </li></ul></ul><ul><ul><li>Quietest Output Reading </li></ul></ul>
  9. 9. Simplified Block Diagram
  10. 10. Temperature Data Format <ul><li>Temperature data can only be read from the Local and Remote Temperature registers. </li></ul><ul><li>Remote temperature data with the digital filter off is represented by an 10-bit plus sign, two's complement word and 11- bit unsigned binary word with an LSB equal to 0.125°C. </li></ul><ul><li>Remote temperature data with the digital filter on is represented by a 12-bit plus sign, two's complement word and 13- bit unsigned binary word with an LSB equal to 0.03125°C (1/32°C). </li></ul>13-bit, 2's complement (12-bit plus sign)
  11. 11. SMBus Interface <ul><li>The SMBDAT output is an open-drain output and does not have internal pull-ups. </li></ul><ul><li>The maximum resistance of the pull-up to provide a 2.1V high level. </li></ul><ul><li>The LM95245 never drives the SMBCLK line and it does not support clock stretching. </li></ul>
  12. 12. Typical Application
  13. 13. Application Hints <ul><li>Compensating for Different Non-Ideality and Series Resistance </li></ul><ul><li>PCB Layout For Minimizing Noise: 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 LM95245's pins </li></ul><ul><li>Noise coupling into the digital interface lines of the RDTS device can also cause havoc in a system </li></ul><ul><li>Noise coupling into the digital lines greater than 400 mVP-P (typical hysteresis) or undershoot less than 500 mV below GND, may prevent successful SMBus communication with any digital sensor or hardware monitor </li></ul><ul><li>To measure temperature external to the LM95245'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 LM95245's temperature. </li></ul><ul><li>The LM95245's BJT Beta Compensation TruTherm technology allows accurate sensing of integrated thermal diodes. </li></ul>
  14. 14. Typical Performance Characteristics LM95245 typical performance with a variety of Intel processors
  15. 15. Additional Resource <ul><li>For ordering LM95245, please click the part list or </li></ul><ul><li>Call our sales hotline </li></ul><ul><li>For more product information go to </li></ul><ul><ul><li> </li></ul></ul><ul><li>Visit Element 14 to post your question </li></ul><ul><ul><li> </li></ul></ul><ul><li>For additional inquires contact our technical service hotline or even use our “Live Technical Chat” online facility </li></ul>