TIDUF13 November   2022 ADS117L11 , ADS127L11 , ADS127L14 , ADS127L18

 

  1.   Description
  2.   Resources
  3.   Features
  4.   Applications
  5.   5
  6. 1System Description
    1. 1.1 Key System Specification
  7. 2System Overview
    1. 2.1 Block Diagram
    2. 2.2 Design Considerations
      1. 2.2.1 Signal-Chain Voltage Levels
        1.       12
      2. 2.2.2 ADC Configuration
      3. 2.2.3 ADC Clocking and Synchronization
      4. 2.2.4 Differential Low-Pass Filter
      5. 2.2.5 Current Source
      6. 2.2.6 Gain Stage and High-Pass Filter
    3. 2.3 Highlighted Products
      1. 2.3.1 ADS127L11
      2. 2.3.2 THS4551
  8. 3System Design Theory
    1. 3.1 IEPE Sensor
      1. 3.1.1 IEPE Sensor Parameters
        1. 3.1.1.1 Sensitivity and Measurement Range
        2. 3.1.1.2 Excitation, Output Bias Voltage, and Output Impedance
        3. 3.1.1.3 Linearity and Temperature Variance
        4. 3.1.1.4 Frequency Response
        5. 3.1.1.5 Noise and Dynamic Range
  9. 4Hardware, Software, Testing, and Test Results
    1. 4.1 Hardware Description
      1. 4.1.1 Board Interface
      2. 4.1.2 Power Configuration
        1. 4.1.2.1 Power Sequence
        2. 4.1.2.2 Analog Supply
        3. 4.1.2.3 Digital Supply
        4. 4.1.2.4 Excitation Current Supply
        5. 4.1.2.5 SPI Connectivity Modes and Their Assembly Variants
          1. 4.1.2.5.1 Daisy-Chain Mode
          2. 4.1.2.5.2 Parallel SDO Mode
          3. 4.1.2.5.3 Parallel SDI Mode and Parallel SDO Mode
          4. 4.1.2.5.4 Clocking Modes
    2. 4.2 Software Requirements
    3. 4.3 Test Setup and Procedure
      1. 4.3.1 Noise Floor and SNR
      2. 4.3.2 Gain and Input Range
      3. 4.3.3 Crosstalk
      4. 4.3.4 Total Harmonic Distortion
      5. 4.3.5 Clock Image Rejection
      6. 4.3.6 Synchronization of the ADCs
      7. 4.3.7 Fault Detection Circuit
    4. 4.4 Test Results
      1. 4.4.1 Noise Floor and Dynamic Range
      2. 4.4.2 Gain and Input Range
      3. 4.4.3 Crosstalk
      4. 4.4.4 Total Harmonic Distortion
      5. 4.4.5 Clock Image Rejection
      6. 4.4.6 Synchronization of the ADCs
      7. 4.4.7 Fault Detection Circuit
      8. 4.4.8 Test With Actual IEPE Sensor
      9. 4.4.9 Measurement Results Summary
  10. 5Design and Documentation Support
    1. 5.1 Design Files
      1. 5.1.1 Schematics
      2. 5.1.2 BOM
    2. 5.2 Software
    3. 5.3 Documentation Support
    4. 5.4 Support Resources
    5. 5.5 Trademarks
  11. 6About the Author

4.1.2.4 Excitation Current Supply

The onboard excitation current section requires high voltage to satisfy high compliance range. The board features an onboard booster stage that generates 24 V out of the input which can range from 1.8 V to 5.5 V, best practice is using the use of the same source of the analog LDO, 5.2 V.

To use the onboard booster:

  • Make sure the analog supply is connected (D2 is on)
  • Connect the external source (5.2 V) to J3
  • Short J11, verify that J12 is unconnected, D3 turns on when the supply is active
  • Current can be measured using an ammeter instead of the short on J11. The estimated current is about 16 mA. The voltage when measured at J11 is not exactly 24 V but is about 23.8 V due to LDO drop.

The estimated current from the 5.2-V analog supply of the booster is below 100 mA.

If external supply is used:

  • Make sure the analog supply is connected
  • Make sure J11 is open
  • Connect the external high voltage source (8 V to 36 V, typical 24 V) to J12, D3 turns on

The estimated current from the high voltage external supply is 16 mA.

Note: To measure the input and output ripples of the booster stage, use test points TP5, TP6.