SBAS940 December 2018 DAC8742H
In this design the DAC8742H internal reference and bandpass filter was chosen to optimize board area, consequently reducing form factor and cost. X7R, 10% accurate, bypass capacitances of 1-µF and 0.1-µF values were chosen for the reference and supplies, respectively.
The DAC8742H device interfaces with the MSP430FR5969, or other similar host controller, through a standard UART interface. The DAC8742H digital pins connected through this interface include UART_RTS, UART_OUT (TX), UART_IN (RX), and CD.
The remaining portion of the schematic includes other TI devices that aid in the realization of a highly accurate 4-mA to 20-mA, 2-wire transmitter. This combination of circuitry is ideally suited for remote signal conditioning of a wide variety of sensors and transducers, including thermocouples, RTDs, thermistors, and strain gauge bridges.
The two-wire transmitter is powered from an external DC power supply that is connected via the two BUS supply lines. The transmitter communicates by sourcing a 4-mA to 20-mA current through the connected bus, and back to the central host, which is typically a PLC analog input module. This expressed range of 4 mA to 20 mA is typically employed to adhere to industry standard, and ensures that the transmitter receives a minimum of 4 mA for correct powered operation.