SNAA416A April   2025  – June 2025 LMK3C0105-Q1

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction
  5. 2Test Setup
    1. 2.1 Board Variation Summary Table
    2. 2.2 Schematics
    3. 2.3 Layouts
    4. 2.4 Stack-Up
  6. 3CISPR-25
    1. 3.1 CISPR-25 Summary
    2. 3.2 CISPR-25 Results
      1. 3.2.1 Monopole
      2. 3.2.2 Bi-Conical
      3. 3.2.3 Log-Periodic
      4. 3.2.4 Horn
  7. 4CISPR-32
    1. 4.1 CISPR-32 Summary
    2. 4.2 CISPR-32 Results
  8. 5Summary
  9. 6References
  10. 7Revision History

1 Introduction

Electromagnetic interference (EMI) is any unwanted interference in an electrical circuit caused by an external source. EMI can be categorized as conducted or radiated. Conducted EMI is a form of conduction coupling caused by parasitic impedance, power, and ground connections. Radiated EMI is the coupling of unwanted signals from radio transmission. This report focus on radiated EMI.

The LMK3C0105-Q1 is a clock generator capable of replacing up to five LVCMOS oscillators (XOs). The part uses an internal BAW oscillator as a reference, along with two fractional output dividers for up to two frequency domains (Figure 1-1). Through the use of BAW technology, the LMK3C0105-Q1 can provide increased flexibility and clocking stability when compared to a quartz oscillator (Table 1-1).


LMK3C0105-Q1 Functional Block Diagram

Figure 1-1 LMK3C0105-Q1 Functional Block Diagram
Table 1-1 BAW vs. Quartz Oscillator
Parameter BAW Technology Quartz Oscillator Technology
Frequency Flexibility BAW oscillator devices supports multiple frequencies with single die Frequency limitations. Different frequencies need different crystals.
Temperature Stability BAW has ±10ppm from -40°C to +105°C As temperature increases, so does ppm stability.
Vibration Sensitivity

BAW meets MIL_STF_883F Method 2002 Condition

(Typical is 1ppb/g)

Typically does not pass MIL-STD

Can be as high as >10ppb/g
Mechanical Shock BAW meets MIL_STD_883F Method 2007 Condition B

Typically does not pass MIL-STD

Can fail at 2,000g

Longer PCB traces are often necessary to reach various end devices when multiple oscillators are replaced with a clock generator, such as the LMK3C0105-Q1. Using longer traces for clock generator routing can result in worse EMI performance than using multiple oscillators, which can be placed close to each end device.

This application note intends to reduce the EMI concern of the LMK3C0105-Q1 and showcase different layout techniques to improve EMI performance.