SLYT847 May   2024 DAC161S997 , DAC8551 , TVS3301

 

  1.   1
  2. 1 Introduction
  3. 2 4mA to 20mA transmitter basics
  4. 3 4mA to 20mA transmitter design aspects
  5. 4 Design performance metrics
  6. 5 Transmitter circuit implementations
  7. 6 Dedicated loop converter
  8. 7 Loop transmitter device
  9. 8 MCU integrated DAC
  10. 9 PWM-based DAC
  11. 10Stand-alone low power DAC
  12. 11Implementations Comparison
  13. 12Conclusion
  14. 13Related websites

10 Stand-alone low power DAC

Using a low-power, stand-alone DAC to realize a 4mA to 20 mA transmitter such as the AFE88101 in Figure 8 achieves the best resolution and linearity performance. To reduce power further, a low-power voltage reference such as the REF35125 can reduce current down to 180µA. Additionally, the AFE88101 has extensive diagnostic features, including a 12-bit ADC and a defined fail-safe mode.

The AFE881H1 is pin-to-pin compatible with the AFE88101, with an integrated HART modem for a compact HART-enabled transmitter. The AFE881H1 has low current consumption when HART is enabled. A HART modem typically consumes 10µA during operation, making it the device of choice for low-power, HART-enabled transmitters. Another feature of the AFE88101 is compatibility with 1.8V logic to allow low-voltage digital operation and reduce power further on the MCU input/output side, as well as reducing electromagnetic emissions.

Two-wire 4mA to 20mA transmitter implemented using the AFE88101. Figure 8 Two-wire 4mA to 20mA transmitter implemented using the AFE88101.

A lower-cost variant with the DAC8311 DAC, LDO and external low-power reference runs with 130µA of current and still achieves reasonable performance.