Single Chip 2-Wire Loop Powered, 4 to 20mA Current Loop RTD Temperature Transmitter Reference Design


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Key Document


In general, for portable 2-wire 4 to 20mA current loop applications, the system power consumption needs to be considered carefully. The conventional approach of using a high bridge excitation voltage and an operational amplifier to achieve a full-scale ADC input voltage increases chip count and overall power consumption. An additional external voltage regulator is also needed to excite the bridge sensor and supply the microcontroller from the same voltage source. Since the goal for this reference design is to maintain low power consumption and low cost solution. This solution utilizes the integrated ADC and operational amplifiers (OAs) of a microcontroller. In order to cut down the cost, the ADC/DAC use the main supply voltage as its reference voltage instead of including an external reference or selecting a more expensive ADC/DAC that features an internal reference. Leveraging the integrated peripherals of MCU enables low component count and low cost. This reference design is based on a mixed signal microcontroller, specifically an MSP430F2274.

  • Analog functionality fully integrated into microcontroller
  • Sensor input compatible with 2-wire PT100 RTD probe only
  • Temperature range for RTD -200°C to +850°C
  • Input power supply range: 10V to 33V DC
  • 4 to 20mA current loop output signal
  • Maximum measured error: better than ±2.5ºC
  • Implements ratiometric measurement
  • Design to meet IEC 61000-4 requirement
  • Operating temperature range -40°C to +85°C

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TI Devices (2)

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Part Number Name Product Family Sample & Buy Design Kits & Evaluation Modules
MSP430F2274  16-bit Ultra-Low-Power Microcontroller, 32KB Flash, 1K RAM  MSP430 ultra-low-power MCUs  Sample & Buy View Design Kits & Evaluation Modules
TPS7A16  60V, 5µA Iq, 100mA Low-Dropout (LDO) Voltage Regulator With Enable and Power Good  Power management  Sample & Buy View Design Kits & Evaluation Modules

CAD/CAE symbols

Part # Package | Pins CAD File (.bxl) STEP Model (.stp)
MSP430F2274 Download -
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TPS7A16 Download Download
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Technical Documents

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User guides (1)
Title Abstract Type Size (KB) Date Views TI Recommends
PDF 10401 30 Jan 2015 26
Design files (5)
Title Abstract Type Size (KB) Date Views
ZIP 1222 30 Jan 2015 4
PDF 161 30 Jan 2015 3
ZIP 301 30 Jan 2015 9
PDF 43 30 Jan 2015 5
PDF 653 30 Jan 2015 23
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Reference Designs  ( 5 )

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