TIDA-00247: Temp. Sensor, 2-Wire 4-20mA Loop

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.