AN 769: Intel FPGA Remote Temperature Sensing Diode Implementation Guide

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ID 683139
Date 4/06/2022
Public
Document Table of Contents
Document Table of Contents x
1. Introduction 2. Implementation Overview 3. Implementation Consideration 4. Evaluation Results 5. Conclusion 6. Document Revision History for AN 769: Intel FPGA Remote Temperature Sensing Diode Implementation Guide
3. Implementation Consideration x
3.1. Ideality Factor (η-Factor) Mismatch 3.2. Series Resistance Error 3.3. Temperature Diode Beta Variation 3.4. Differential Input Capacitor 3.5. Offset Compensation
4. Evaluation Results x
4.1. Evaluation with Maxim Integrated* 's MAX31730 Temperature Sensing Chip Evaluation Board 4.2. Evaluation with Texas Instruments* 's TMP468 Temperature Sensing Chip Evaluation Board
1. Introduction
2. Implementation Overview
3. Implementation Consideration
4. Evaluation Results
5. Conclusion
6. Document Revision History for AN 769: Intel FPGA Remote Temperature Sensing Diode Implementation Guide

2. Implementation Overview

The external temperature sensing chip connects to the Intel® FPGA remote TSD. The remote TSD is a PNP or NPN diode-connected transistor.
Figure 1. Connection Between Temperature Sensing Chip and Intel® FPGA Remote TSD (NPN Diode)


Figure 2. Connection Between Temperature Sensing Chip and Intel® FPGA Remote TSD (PNP Diode)


The following equation forms the temperature of a transistor in relation to the base-emitter voltage (VBE).

Equation 1. Relationship Between Temperature of Transistor to Base-Emitter Voltage (VBE)



Where:

  • T—Temperature in Kelvin
  • q—the electron charge ( )
  • VBE —base-emitter voltage
  • k—Boltzmann constant ( )
  • IC —the collector current
  • IS —the reverse saturation current
  • η—the ideality factor of the remote diode

Rearranging Equation 1, you get the following equation.

Equation 2. VBE



Typically, the temperature sensing chip forces two consecutive well-controlled currents, I1 and I2 on the P and N pins. The chip then measures and averages the change of the VBE of the diode. The delta in VBE is directly proportional to the temperature, as shown in Equation 3.

Equation 3. Delta in VBE



Where:

  • n—forced current ratio
  • VBE1 —base-emitter voltage at I1
  • VBE2 —base-emitter voltage at I2
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