How can I reduce EMI in my design?
Submitted By: Craig Steiner FAQ Last Modified: 07/10/06
- It can be helpful to insert 10...47Ohm resistors at outputs of 74HC541 for cables leaving or entering board.
- Put a soft ferrite in series with Vcc as close as possible to pin 40 of the MCU, with a dedicated filter cap between it and the MCU. On a 2-layer board this is sometimes the only way to control EMI.(Blast that 20-40 ground/power arrangement).
- For cables carrying signals from one board to the other It's a good idea to use a flat cable for this purpose where every other or every third line is a ground line. All these ground lines MUST be connected to ground at each board.
- Switching SSRs can produce some interference. Also, via cables to outer world interference is fed very near to your microcntroller circuit. This can cause problems. You should keep microcontroller circuitry and output side of SSRs much much farther away from each other. Sometimes, it can be helpful even to add a metal plate placed close over the micro board and connected to ground plane at several places. This metal plate will act as a shield: Every stray capacitance to the SSRs and their loads will end on this metal plate, and not inside your micro circuitry.
- Keep the microcontroller clock & logic speed at a minimum. Make it just enough to run the application.
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