SNAU293 May   2024 LMX1860-SEP

 

  1.   1
  2.   Description
  3.   Features
  4.   Applications
  5.   5
  6. 1Evaluation Module Overview
    1. 1.1 Introduction
    2. 1.2 Kit Contents
    3. 1.3 Specification
    4. 1.4 Device Information
  7. 2Hardware
    1. 2.1 Setup
      1. 2.1.1  Evaluation Setup Requirement
      2. 2.1.2  Connection Diagram
      3. 2.1.3  How to Enable Full SPI Control
      4. 2.1.4  Power Requirements
      5. 2.1.5  Pin Mode Strapping
      6. 2.1.6  Reference Clock
      7. 2.1.7  Output Connections
      8. 2.1.8  Header Information
      9. 2.1.9  Default Configuration
      10. 2.1.10 How to Generate SYSREF
      11. 2.1.11 Multiplier Mode Example
      12. 2.1.12 Divider Mode Example
      13. 2.1.13 Hybrid Mode: SPI and Pin Mode
  8. 3Software
    1. 3.1 Software Installation
    2. 3.2 Software Description
    3. 3.3 USB2ANY Interface
  9. 4Implementation Results
    1. 4.1 Buffer, Divider, and Multiplier Modes
    2. 4.2 SYSREF Generation
    3. 4.3 SYSREF Delay Generators
  10. 5Hardware Design Files
    1. 5.1 Schematic
    2. 5.2 PCB Layout
    3. 5.3 PCB Layer Stack-Up
    4. 5.4 Bill of Materials
  11. 6Additional Information
    1. 6.1 Troubleshooting Guide
      1. 6.1.1 General Guidance
      2. 6.1.2 If Output Is Not Seen on CLKOUT
      3. 6.1.3 If Device Features Are Not Active
      4. 6.1.4 If Multiplier Frequency Is Not Accurate
      5. 6.1.5 If Divider Frequency Is Not Accurate
      6. 6.1.6 If SYSREF Is Not Observed
    2. 6.2 Trademarks

6.1.6 If SYSREF Is Not Observed

There are several settings which must be correct to achieve SYSREF outputs.

  • Make sure of the following settings:
    • Set SYSREF_MODE to Continuous (for debugging).
    • SYSREFREQ_MODE field set to SYSREF mode.
    • SYSREFREQ_VCM set for DC-coupled, with about 1.1V on SYSREFREQ_P and 1.5V on SYSREFREQ_N.
    • SYSREF_DELAY_BYP field set to use delay.
    • SYSREF_EN=1.
  • Make sure the frequencies of the SYSREF_DELAY_DIV and SYSREF_DIV_PRE are correctly configured. The GUI highlights any frequency violations.
  • Make sure that FINTERPOLATOR % FSYSREF = 0. The GUI highlights the SYSREF divider in case of violations.
  • Make sure that the output channel (CHx_EN/LOGIC_EN) and the SYSREF buffer (SYSOUTx_EN / LOGISYS_EN) are enabled.
  • Confirm that Windowing mode is not enabled on the User Controls page (SYSWND_EN=0).
  • Confirm that R15[9]=1. This is set automatically by the GUI, so this potential root cause is rare.
  • Confirm the 1.1V and 1.5V source for SYSREFREQ_N and SYSREFREQ_P respectively are actually resulting in the required voltages at the pins. If power supplies are used for these voltages, then for the supplies to be unable to sink current is uncommon. The 1.1V source is not able to sink current from the 1.5V supply through the internal 100Ω impedance. An arbitrary function generator is recommended if possible.