TIDUF19 September   2022 ADS1282-SP

 

  1.   Description
  2.   Resources
  3.   Features
  4.   Applications
  5.   5
  6. 1System Description
  7. 2System Overview
    1. 2.1 Block Diagram
    2. 2.2 Design Considerations
      1. 2.2.1 Rset, Rref, and Gain Calculation
      2. 2.2.2 Analog Multiplexer Effect
    3. 2.3 Highlighted Products
      1. 2.3.1 ADS1282-SP
      2. 2.3.2 LMP7704-SP
      3. 2.3.3 TPS7A4501-SP
      4.      16
  8. 3Hardware, Software, Testing Requirements, and Test Results
    1. 3.1 Hardware Requirements
    2. 3.2 Software Requirements
    3. 3.3 Test Setup
    4. 3.4 Test Results
  9. 4Design and Documentation Support
    1. 4.1 Design Files
      1. 4.1.1 Schematics
      2. 4.1.2 BOM
    2. 4.2 Documentation Support
    3. 4.3 Support Resources
    4. 4.4 Trademarks
  10. 5About the Author

2.2.2 Analog Multiplexer Effect

Analog multiplexer (Mux) is not implemented in the design hardware, but the Mux is considered through simulation.

GUID-20220822-SS0I-RB8C-TW4N-JLT3KQB64ZKN-low.png Figure 2-3 Analog Multiplexer Effect Simulation
Table 2-2 Analog Multiplexer Effect Simulation Results
Without Mux With mux % difference
ADCin1 [mV] 179.070457 179.07009 0.0002%
ADCin2 [mV] 29.845079 29.845018 0.0002%

As shown in Figure 2-3 and Table 2-2, the RTD board is simulated with and without mux, and their schematic are shown on the right and left side of the figure, along with simulation result circled in red and black. To simulate a mux, a resistor to represent the MUX on-resistance is added and set to 1 kΩ allowing 50 Ω difference between each channel. Since ADS1282-SP has one GΩ differential input impedance with PGA chopping enabled, there are only about 0.0002% difference between the two circuits output. Compare this error with the error causing by the RTD itself, the error from mux is negligible and does not affect the overall performance.