SBOA594 August   2024 OPA2990

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1 Introduction
  5. 2 Circuit Description
  6. 3 Supporting Multiple Output Ranges
  7. 4 Resistor Sizing, M2 Selection, and Other Design Considerations
  8. 5 Mode and Range Control
  9. 6 Supply Level for Current Output
  10. 7 Supply Levels for Voltage Output
  11. 8 Protection Features
  12. 9 Measurement Results
  13. 10Power Consumption
  14. 11Error Monte-Carlo Analysis
  15. 12Rise and Fall Times
  16. 13Building Multi-Channel Output
  17. 14Summary
  18. 15References

3 Supporting Multiple Output Ranges

If the circuit is required to support multiple output ranges, the circuit has to do that through changing input and reference ranges, as the stage gain is fixed. Making the gain adjustable can complicate the design and add inaccuracies.

Table 3-1 shows the different configurations for the same stage to support multiple output ranges:

Table 3-1 Configurations for Different Ranges
0-20mA 4-20mA 0 to 10 0 to 5 -10 to 10
VREF switches S1 open S1 closed S2 open S2 open S2 closed
VIN range 0-2.5 0-2.5 0-2.5 0-1.25 0-2.5
R ratios R 5 R 3 ∙ R 4 = 0 . 008 R 1 R 1 + R 2 = 0 . 2 R 8 R 7 = 3 R 8 R 9 = 4

Table 3-1 shows that different output ranges can be achieved by controlling the different switches, and the input range, with the resistor ratios remaining constant.

A DAC source which has 2.5V or 1.25V full-scale is required to drive the stage, as well as a 2.5V reference.