TIDUF45 May   2024

 

  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 ADS127L21
      2. 2.3.2 PGA855
      3. 2.3.3 REF70
  9. 3System Design Theory
  10. 4Hardware, Software, Testing Requirements, and Test Results
    1. 4.1 Hardware Description
      1. 4.1.1 Board Interface
      2. 4.1.2 Power Supplies
      3. 4.1.3 Clocking Tree
    2. 4.2 Software Requirements
    3. 4.3 Test Setup
    4. 4.4 Test Results
      1. 4.4.1 DC Accuracy Tests
      2. 4.4.2 Gain and Offset Temperature Drift
      3. 4.4.3 Nonlinearity
      4. 4.4.4 SNR and Noise Performance
  11. 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
  12. 6About the Author

4.1.3 Clocking Tree

The board supports three different clock options:

  • PHI clock (no external connections)
  • Local clock (no external connections)
  • External, user-supplied clock

The default position for jumper (JP7) is 2-3, which routes the PHI digital controller board clock to the CLK pin on the ADS127L21 (U3). If the board is used without the PHI controller, then the jumper can be moved to 1-2 to directly route the local clock to ADS127L21.

Jumper (JP6) 2-3 enables the local 32.768MHz oscillator (Y1) on the board, which is the default position required to work with the ADS127L21EVM-PDK-GUI software. If inactive (JP6) 1-2, allows an external clock supplied on the SMA connector (J14).

The ADS127L21EVMPDK-GUI software by default uses the 32.768MHz (Y1) oscillator, but can also select the 24MHz PHI clock source. An external clock source can be used by placing jumper JP6 in the 1-2 position. A CMOS square-wave signal with an amplitude equal to IOVDD (2.5V when using the PHI board) must be used with a frequency within the specified range of the ADS127L21.