EMI/EMC design tips for NHD-4.3-480272EF-ATXL#

FJAcontrolesSA

• December 09, 2016 09:07

Hello everyone,

We use the NHD-4.3-480272EF-ATXL# TFT display in the front console of one of our product designs (a 19'' rack mounted industrial control unit). We resently did some pre-compliance testing for EMC and during the emission test we had a big chunk of interference around 200MHz which seemed to be related to the display (i.e. turning it off made the interference go away).

We did not put much care to the EMI desing of the front consola assembly (and it shows!), so now we a reviewing the design with this in mind and I had a couple of questions:

1) Should the TFT bezel be grounded?
2) We are making sure that all TFT signals are now running over a solid ground plane for both signal integrity and reduced emissions. What should the trace impedance be? Is 50ohm OK?

Any other tips will be much appreciated!

Thank you all in advance.

Cheers

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  Paul_B

  • December 09, 2016 11:07

  Below are a few tips that should help improve your design:
   
  •   Ground the TFT's bezel
  •   Utilize flat cable Ferrite core (used for FPC/FFC cable)
  •   Utilize EMI shielding foils and film
  •   Place 33 Ohm resistors in series on the display lines to help improve EMI performance
  
  Please note that the bezel can act as a shield keeping noise from other system components it must be well grounded to provide the best immunity.
  
  Shielding techniques can go a long way toward reducing electromagnetic/RF interference (EMI) and delivering reliable systems.
  
  Hope this helps, feel free to contact me if you have any questions or concerns.

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  Joachim Geiger

  • January 23, 2017 11:07

  Dear Paul,
  we use also the NHD-4.3-480272EF-ASXN#-T for a electric drive visualisation for ultralight planes.
  There are strong emissions at 120Mhz, the frequency for the aeronautical radio service, comming from the display.
  You wrote about the possiblity to reduce EMI with 33 ohm resistors in series to the display lines, and/or ferrite's for the FFC-Cable.
  Is there a scheme available in which lines the resistors should be placed and how to use the ferrite's?
  
  Thank you in advance.

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  tiro

  • October 16, 2017 11:07

  Ferrite and resistor you must place close as possible to clock (emission) source. In this case I think that your I/O port in microcontroller.

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