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Isolated Thermocouple

Isolated Thermocouple System from Texas Instruments.

Block Diagram


2.048 V/4.096 V Reference Amplifier ADC ADC DOUT Isolator ADC DOUT Isolator ADC SCLK Isolator ADC SCLK Isolator Clock Clock Clock Isolated DC/DC Converter Low Power MCU MCU System Power Op-Amp Op-Amp System Power USB-to-Serial Port Controller Voltage Reference

Design Considerations

Isolated Thermocouple:

The ITC (Isolated Thermocouple) block diagram shown comes from an actual Texas Instruments reference design and is designed to provide repeatable temperature measurements in high noise environments. It features electrical isolation between the analog -front end- (INA326 instrumentation amplifiers, ADS1244 24 bit Analog to Digital Converter) and the digital -back end- (MSP430F122, TUSB3410).

The selected integrated circuit components are ideally suited to this application, and include:

  • INA326 Precision Instrumentation Amplifier
    - Low Input Offset Voltage (100 uV maximum)
    - Low Offset Drift (0.4 uV per degree Centigrade maximum)
    - Very Low 1/f Noise
    - High CMRR (114 dB Typical, 94 DB Minimum)
     
  • ADS1244 24 bit Analog to Digital Converter
    - 0.0002% INL (Typical), 0.0008% Maximum
    - Simultaneous 50Hz and 60Hz Rejection
    - Effective Number of Bits (ENOB): 20
     
  • ISO721M High Speed Digital Isolator or ISO7221M (dual)
    - Insulation Resistance
    - Insulation Voltage: 560 Volts
     
  • DCR010505 Isolated, Regulated DC/DC Converter
    - Input to Output Capacitance: 25 pF (Typical)
    - Isolation breakdown voltage: 1000 Vrms
     
  • MSP430F122 16 Bit Ultra Low Power Microcontroller
    - Built in Serial Communications Interface (UART)
     
  • TUSB3410 USB to Serial Port Controller
    - Displays information and video/graphic on the LCD panel.
     

Application Notes

  • Flash Programming Solutions for the TMS320F28xxx DSCs (spraal3.htm, 8 KB)
    19 Aug 2008 Abstract
    

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