Hi, Following a successful EMC test (to meet directive 2014/53/EU), the test house identified a ~30MHz signal. Luckily 7db under class B limit. Following a spot of near field probing, it turns out that the RS232 driver (incorporating a charge pump) was the likely culprit. See enclosed. I've revisited the datasheet & I'm still left a bit stumped. Does anyone have any clues or theories as to why we might be observing this? Nothing else on the board oscillates at this frequency & much of the square wave ringing has been damped elsewhere, so I don't think this is harmonic. TI suggests that the charge pump operates at 100-200KHz.
Pete