SCAS892D February   2010  – July 2025 CDCE937-Q1 , CDCEL937-Q1

PRODUCTION DATA  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Device Comparison Table
  6. 5 Pin Configuration and Functions
  7. 6 Specifications
    1. 6.1 Absolute Maximum Ratings
    2. 6.2 ESD Ratings
    3. 6.3 Recommended Operating Conditions
    4. 6.4 Thermal Information
    5. 6.5 Electrical Characteristics
    6. 6.6 Timing Requirements
    7. 6.7 Typical Characteristics
  8. 7 Parameter Measurement Information
  9. 8 Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1 Control Terminal Setting
      2. 8.3.2 Default Device Setting
    4. 8.4 Device Functional Modes
      1. 8.4.1 SDA and SCL Serial Interface
    5. 8.5 Programming
      1. 8.5.1 Data Protocol
      2. 8.5.2 Command Code Definition
      3. 8.5.3 Generic Programming Sequence
      4. 8.5.4 Byte Write Programming Sequence
      5. 8.5.5 Byte Read Programming Sequence
      6. 8.5.6 Block Write Programming Sequence
      7. 8.5.7 Block Read Programming Sequence
      8. 8.5.8 Timing Diagram for the SDA and SCL Serial Control Interface
      9. 8.5.9 SDA and SCL Hardware Interface
  10. 9 Register Maps
    1. 9.1 SDA and SCL Configuration Registers
  11. 10Application and Implementation
    1. 10.1 Application Information
    2. 10.2 Typical Application
      1. 10.2.1 Design Requirements
      2. 10.2.2 Detailed Design Procedure
        1. 10.2.2.1 Spread-Spectrum Clock (SSC)
        2. 10.2.2.2 PLL Frequency Planning
        3. 10.2.2.3 Crystal Oscillator Start-Up
        4. 10.2.2.4 Frequency Adjustment With Crystal Oscillator Pulling
        5. 10.2.2.5 Unused Inputs and Outputs
        6. 10.2.2.6 Switching Between XO and VCXO Mode
      3. 10.2.3 Application Curves
    3. 10.3 Power Supply Recommendations
    4. 10.4 Layout
      1. 10.4.1 Layout Guidelines
      2. 10.4.2 Layout Example
  12. 11Device and Documentation Support
    1. 11.1 Documentation Support
      1. 11.1.1 Related Documentation
    2. 11.2 Receiving Notification of Documentation Updates
    3. 11.3 Support Resources
    4. 11.4 Trademarks
    5. 11.5 Electrostatic Discharge Caution
    6. 11.6 Glossary
  13. 12Revision History
  14. 13Mechanical, Packaging, and Orderable Information

10.2.2.1 Spread-Spectrum Clock (SSC)

Spread-spectrum modulation is a method to spread emitted energy over a larger bandwidth. In clocking, spread spectrum can reduce electromagnetic interference (EMI) by reducing the level of emission from the clock distribution network.

CDCE937-Q1 CDCEL937-Q1 Comparison Between Typical Clock Power Spectrum and Spread-Spectrum Clock
CDCS502 with a 25MHz crystal, FS = 1, fOUT = 100MHz, and 0%, ±0.5, ±1%, and ±2% SSC
Figure 10-3 Comparison Between Typical Clock Power Spectrum and Spread-Spectrum Clock

Spread-spectrum clocking can be used to help reduce EMI to meet design specifications. For example, a specified EMI threshold of 55dB/mV requires ±1% spread-spectrum clocking to meet this requirement.