Silicon Based Temp Sensor Primer TI Information Selective

Silicon Based Temp Sensor Primer TI Information – Selective Disclosure 1

How does a Si temp sensor work? • A silicon temperature sensor measures the changes in base-emitter voltage due to temperature with a known pair of fixed precision currents. The currents through a p-n junction are given by the following equations: IF Is VBE η k T q • Forward current Saturation current Base Emitter Voltage Process non-ideality factor Boltzmann’s constant (1. 38 x 10 -23 J/K) Absolute Temperature in K Electron charge constant (1. 6 x 10 -19 C) The change in base-emitter voltage produces Proportional-to-Absolute (PTAT) voltage which is immune to most variations in process. The temperature is calculated from this PTAT voltage: 2

Remote vs. Local Temperature Sensing Local Remote Advantages • • • Inexpensive Easy to use Good noise immunity No external transistor required Excellent accuracy and temperature range • Extremely Linear • Multi-channel available; allows temperatures to be monitored for more than 1 location • Measure direct die temp of CPUs/GPUs • Not required to be close to temperature source • Good accuracy and temperature range • Extremely Linear Disadvantages • Must be proximal to source • Only 1 temperature reading from 1 location • Remote Diode or transistor required • Higher Noise sensitivity • Not as accurate as local temp sensor • N-factor calibration required 3

Error Effect of Noise in a Remote Diode Junction Example of Noise in a remote diode junction 4

What is the fix for EMI/RFI from a noisy remote junction? • Add series resistance to attenuate capacitor “sampling” effect • Remove the Differential “Filter” capacitor • Add Ferrite Beads with a cutoff of 200 MHz • If possible, use twisted pairs from the remote source to the temperature sensor • Use good bypassing at the supply pins 5

Thermal Management Solutions Local Analog Local Digital Remote Digital Voltage output proportional to temperature Reports temperature at location of the sensor Measure any Diode, Transistor, or CPU/GPU/FPGA Smallest: Highest Accuracy Lowest Power: Highest Temp: Most Popular: LM 20 LM 57 LM 94022 LM 34 LM 50 LM 94023 TMP 20 Smallest: Lowest Power: Highest Temp: Highest Accuracy: Ind. Standard: TMP 112 TMP 102 LM 95172 TMP 275 LM 75 TMP 103 Switches/Thermostat Measures passive IR to determine object temperature without making contact Simple hardware over temperature protection World’s First: TMP 006 LM 56 TMP 708 TMP 302 TMP 303 LM 95234 TMP 512 TMP 44 x TMP 411 LM 95214 TMP 513 LM 95245 LM 96163 TMP 112 TMP 75 Contactless IR Dual Alerts: Resistor Prog. Pin Programmable: Factory Preset: Highest # of Ch: Int. Power Monitor Beta Correction: Most Popular: LM 57 Fan Control /HW Monitors 2 Wire Interface: Fan Control: Monitor & Control: 6 -ch Comparators: LM 96080 AMC 80 LM 96163 AMC 6821 LMP 92001 LMV 7231 LM 27 6