SLVAFI8 February   2023 TLC6C5748-Q1

 

  1.   Abstract
  2.   Trademarks
  3. 1Introduction
  4. 2Design Considerations for Low EMI
    1. 2.1 Design Considerations Overview
    2. 2.2 Considerations in Detail
      1. 2.2.1 Top-Level Architecture
      2. 2.2.2 High Frequency Signals
        1. 2.2.2.1  Original Setup
        2. 2.2.2.2  3.3 V I/O Voltage Instead of 5 V
        3. 2.2.2.3  Use Independent OSC for GSCLK With Spread Spectrum
        4. 2.2.2.4  Without Using Buffer on GSCLK
        5. 2.2.2.5  Using Snubber on GSCLK
        6. 2.2.2.6  Lower the Signal Frequency
        7. 2.2.2.7  Placement and PCB layout
        8. 2.2.2.8  ESD Enhancement
        9. 2.2.2.9  Demo and Test Results
        10. 2.2.2.10 Bench Test Results
  5. 3Summary
  6. 4References

2.2.1 Top-Level Architecture

In most cases, a local dimming system consists of at least two PCB boards, one is the system board and the other is LED board for backlight. Some designs even have more PCB counts. This architecture could lead to long cables (mostly FPC or FFC) and multiple connector contacts, which introduces relatively high parasitic inductance along the signal path. When the driving current of the high frequency communication signals flowing through, the parasitic inductance could be equalized as an AC noise source. This is one of the dominant reasons of excessive radiated emission.

Minimized PCB counts and connector counts should be considered during the top-level architecture floor planning. Besides, cables and connectors with shield are also recommended to decrease the radiated emission.