When I use one – and as a hobbyist, I like to, because I do one-offs, and beads are cheap –, I look at the frequency-impedance curves, and typically pick the one common one that has high/highest impendance at the frequency range I expect noise to come in or leak out via the supply line. You don't typically see them used in 10MHz microcontroller circuits, but at 48MHz and above, they're common.

From a point of view of EMC control it is sometimes better to not just use the highest impedance bead at your operating frequency but to consider what the impedance is over a wider frequency range.

Fully agreed. I do look at the frequency-impedance curve, and try to estimate (because I don't have test equipment to measure) the expected noise frequencies from clocks and switching frequencies and their harmonics/multiples; after all, a squarish edge at some frequency does have a lot of harmonics at higher frequencies (multiples of the original frequency). Beads do seem to help most with ADC noise, and they are cheap enough that I like to use them in my one-off designs for the EMI rejection they do provide, "just in case".

Some types of beads have a very peaky, high Q response and can only achieve good attenuation over a narrow frequency range but, due to falling impedance at higher frequencies, are less effective at suppressing harmonics. Beads with a lower Q, and hence greater resistive losses, often maintain a higher average impedance over a broader frequency range and thus are more effective at suppressing the difficult higher harmonics.

Well put. This is easily seen in the frequency-impedance curves, even to a hobbyist like myself.

I am not sure if understood about saturation.

Saturation means that when the DC current is high, the impedance with respect to noise on top of that DC decreases: the ability of the bead to "reject" the higher frequency noise decreases.

The same happens with supply bypass capacitors and DC voltage: the higher the voltage, the lower the capacitance with respect to noise on top of that DC. (Well, C0G/NP0 capacitors tend to not suffer from that much, but most capacitor types do.)

We want the ferrite bead to have high impedance at the target frequency range, so that it will "reject" those frequencies.

(Again, I'm using "reject" because some of it is absorbed, most reflected; and the effectiveness is not linearly dependent on the impedance –– it's not "twice the impedance means twice as effective" –– because of that AC reflection.)

For example, the two ferrites I showed won't do anything strange at 3 A current; they will drop about 0.1 V across them, and generate 315 mW of heat, and their impedance at high frequencies –– their ability to "reject" the noise –– is quite low that being their maximum rated current, but they will "work". I chose them as examples, because they're cheap, about 0.06€ in lots of ten at Mouser, very common, have nice wide impedance peaks up to 1 GHz, and seemed to me to fulfill the demands.

The similar ones with the highest current rating I could find at Mouser are

Pulse Electronics BBUP00321611121Y00 (link to datasheet, 6A current rating). It costs about 0.09€ in lots of ten at Mouser.

If we compare its frequency-impedance curve to the Murata ones I linked to earlier, you'll see that the impedance peak in the Pulse one is quite sharp, just like srb1954 described. In particular, the Murata ones have 120 Ω impedance from 80 MHz to 1000 MHz = 1 GHz, whereas the Pulse one exceeds 100Ω impedance only between about 70 MHz and 200 MHz. Thus, higher current rating in this case comes with a much narrower effective frequency "rejection" range.

"Which one to pick, then?" is a difficult question. What is the expected current draw

on that pin? Are there any suggested example ferrite beads mentioned, so one could check the current rating and frequency-impedance curve? But, ferrite beads are not miraculous noise filters, so it is not like the design will fail if you choose the wrong one; you'll simply have more noise/EMI than in the best case.

Given only the information in this thread, I'd pick one of the Murata ones myself. I hope the more experienced members in this thread will give you their opinions.