Hello,
we have some problems in the EMC test.
With the help of a sniffer probe we could determine that the output of the status LED (pin 24,25,26,27) generates a 100MHz signal. Can you explain how we can remove this signal.
To my knowledge chip works at 125 MHz, not sure how 100 MHz can be there, however why not (100=125/5*4). I can’t comment about why you may see it, but obvious mitigation strategies are putting ferrite EMI suppression bead onto the wire (around the wire to suppress emissions outwards). Putting capacitor or more advanced chip ferrite bead into the circuit may need closer consideration because their energy will bounce back to the chip and it is a good question if the chip will withstand it in long term. Probably put buffer chip with known output characteristics just near the LED outputs and then apply LPF to the output of this buffer.
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The IC is using a 25MHz Quarz. I have disconnected the solder pins from the board and it is clearly coming from the IC itself, specifically the lower right corner (pin 24 and pin 25). I don’t quite understand where to put the ferrites.
