TIDUFE3 July   2025

 

  1.   1
  2.   Description
  3.   Resources
  4.   Features
  5.   Applications
  6.   6
  7. 1System Description
    1. 1.1 Key System Specifications
  8. 2System Overview
    1. 2.1 Block Diagram
    2. 2.2 Design Considerations
    3. 2.3 Highlighted Products
      1. 2.3.1 TPS7A03
      2. 2.3.2 REF35
      3. 2.3.3 TVS3301
      4. 2.3.4 OPA391
      5. 2.3.5 AFE881H1
      6. 2.3.6 AFE882H1
      7. 2.3.7 SN74LV8T165
      8. 2.3.8 TMUX1219
  9. 3System Design Theory
  10. 4Hardware, Software, Testing Requirements, and Test Results
    1. 4.1 Hardware Requirements
    2. 4.2 Test Setup
    3. 4.3 Test Results
      1. 4.3.1 Linearity Tests
        1. 4.3.1.1 Linearity Tests Summary
      2. 4.3.2 Noise Tests and Current Histogram
        1. 4.3.2.1 Noise Tests and Current Histogram Summary
      3. 4.3.3 Step Response
        1. 4.3.3.1 Step Response Summary
      4. 4.3.4 Start-Up
      5. 4.3.5 MCU Current
        1. 4.3.5.1 MCU Current Summary
      6. 4.3.6 System Currents
        1. 4.3.6.1 Summary of System Currents
  11. 5Design and Documentation Support
    1. 5.1 Design Files
      1. 5.1.1 Schematics
      2. 5.1.2 BOM
      3. 5.1.3 PCB Layout Recommendations
        1. 5.1.3.1 Layout Prints
    2. 5.2 Tools and Software
    3. 5.3 Documentation Support
    4. 5.4 Support Resources
    5. 5.5 Trademarks
  12. 6About the Author

4.3.1 Linearity Tests

For this test, this reference design is connected to a microcontroller for the SPI of the AFE and the analog output is connected to a power supply and an ammeter. The whole system is run from the current on the loop and interfaced to a PC through an isolated UART. All tests are done with 10V and 24V loop voltage, with AFE881H1 in 3.3V and 1.8V configuration, for AFE882H1 in 3.3V configuration. The DAC code is stepped and the current reading of the ammeter is recorded.

Figure 4-4 shows the complete setup.

TIDA-010982 Test Setup for Linearity TestFigure 4-4 Test Setup for Linearity Test

Figure 4-5 through Figure 4-16 show the linearity including a linear trend line which is also used for calculating the error. Therefore the equation is used to calculate the ideal current and the difference to the measurement is shown. For each 10V to 24V configuration, the same equation is used to calculate the error, simulating a calibration at a bias point and then operating at a different one. The different equations are shown for reference.

TIDA-010982 AFE881: 1.8V Supply, 10V Loop Linearityy = 3.35466E–04x + 2.99760Figure 4-5 AFE881: 1.8V Supply, 10V Loop Linearity
y = 3.35466E–04x + 2.99760
TIDA-010982 AFE881: 1.8V Supply, 24V Loop Linearityy = 3.35485E–04x + 2.99755Figure 4-7 AFE881: 1.8V Supply, 24V Loop Linearity
y = 3.35485E–04x + 2.99755
TIDA-010982 AFE881: 3.3V Supply, 10V Loop Linearityy = 3.35189E–04x + 2.99416Figure 4-9 AFE881: 3.3V Supply, 10V Loop Linearity
y = 3.35189E–04x + 2.99416

TIDA-010982 AFE881: 3.3V Supply, 24V Loop Linearityy = 3.35312E–04x + 2.99208

Figure 4-11 AFE881: 3.3V Supply, 24V Loop Linearity
y = 3.35312E–04x + 2.99208
TIDA-010982 AFE882: 3.3V Supply, 10V Loop Linearityy = 3.19149E–04x + 3.04646Figure 4-13 AFE882: 3.3V Supply, 10V Loop Linearity
y = 3.19149E–04x + 3.04646
TIDA-010982 AFE882: 3.3V Supply, 24V Loop Linearityy = 3.19127E–04x + 3.04673Figure 4-15 AFE882: 3.3V Supply, 24V Loop Linearity
y = 3.19127E–04x + 3.04673
TIDA-010982 AFE881: 1.8V Supply, 10V Loop ErrorFigure 4-6 AFE881: 1.8V Supply, 10V Loop Error
TIDA-010982 AFE881: 1.8V Supply, 24V Loop ErrorFigure 4-8 AFE881: 1.8V Supply, 24V Loop Error
TIDA-010982 AFE881: 3.3V Supply, 10V Loop ErrorFigure 4-10 AFE881: 3.3V Supply, 10V Loop Error
TIDA-010982 AFE881: 3.3V Supply, 24V Loop ErrorFigure 4-12 AFE881: 3.3V Supply, 24V Loop Error
TIDA-010982 AFE882: 3.3V Supply, 10V Loop ErrorFigure 4-14 AFE882: 3.3V Supply, 10V Loop Error
TIDA-010982 AFE882: 3.3V Supply, 24V Loop ErrorFigure 4-16 AFE882: 3.3V Supply, 24V Loop Error