I have a design with STM32L476 microprocessor that I am having EMC issues with. The processor is locking up at 100MHz to 240MHz radiated immunity EMC, 10V/m, and not recovering.
Product Architecture is that there is an external 24V supplying power to an M12 connector, and an analog output in that same cable from a DAC. The M12 feeds the main board through a 1.25�? flex circuit to an FPC connector.
I2C and SPI is routed from the main board to another sensor board (not shown in image) via a 6�? unshielded wire harness.
Putting clip-on ferrites on the wire harness reduced the EMC impact, but I had to use other techniques like covering the unit in tinfoil for it to pass altogether, so I suspect a combination of noise getting in on the main power input line as well as picked up by the harness, and by the PCB itself. The i2C and SPI lines from harness to micro have 1k @ 100MHz ferrites in series with 33 Ohm resistors.
At round 2 of my EMC testing I tacked on 10nF X2Y capacitors across the 24V input and analog output, as well as 100nF feed through capacitors (see attached image). I also added a 2uF capacitor and a 470pF capactor across the DC input. I added 470pF caps in parallel with the groups of micro bypass caps. All of this enabled me to pass conducted immunity, but still I have the radiated immunity that still has issues.
By the way, we had a 1st release of this unit, using batteries only, which passed EMC testing in that version. It seems like the cable is pushing it over the limit. The sensor is also a different type than the battery only version has.
Your help is much appreciated.
