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

9 PWM-based DAC

A more generic approach using an MCU (without an integrated DAC) is to rely on pulse-width modulation (PWM) to generate DAC outputs. A simple PWM DAC has a resolution of 10 bits to 12 bits. However, it is possible to realize a 16-bit resolution DAC with more advanced techniques such as two-path PWM and active ripple suppression.

To achieve a high effective resolution, the PWM signals are buffered using voltage reference-powered logic gates; the MCU needs proper bypassing to avoid digital noise injection into the loop current. The implementation depicted in Figure 7 is low power, stable over temperature, and achieves greater than 13 bits of effective resolution at a very low cost.

Two-wire 4mA to 20mA transmitter implemented using a PWM DAC. Figure 7 Two-wire 4mA to 20mA transmitter implemented using a PWM DAC.