Hello Amy,
EN55022 has both radiated and conducted.
The AN-2125 shows conducted and radiated scans of the LMZ22 LMZ23 EVM.
PCB layout and mechanical enclosure really determine the radiated profile in the LMZ modules.
About the only thing you can do with this type of module is perhaps filter out some high frequency noise on the input bus or output.
For better radiated a mechanical metal shield should be considered.
A simple PI filter made with capacitors and FERRITE BEADS is common.
In the EVM schematic it shows a 150uF followed by a 0.47uF input cap, the PI filter would go before the 150uF.
The output shows a .047uF followed by 2x220uF, the PI filter would go after that.
MAKE SURE the FEEDBACK signal is taken BEFORE the PI filter, not after it.
A Fair-Rite 2773021447 and some 0.001uF (1nF) ceramic caps on each side would make a good PI filter.
Of course any filter might need to be TUNED to work the best for a given application.
Here is an example:
This figure shows a typical input filter. This input filter is a pi-filter that provides up
to 40dB of This pi-filter could also be used as an output filter as well. In this
example, C3 is a 10uF bulk input capacitor for the TPS62050. Looking at the
specifications for the 10uF capacitor shows it has a SRF (series resonant frequency) of 1.925MHz. This means
that C3 can not be used as part of the input filter since it has a poor high frequency
response. To solve this problem, another capacitor, C2, is placed in parallel to
complete the input filter. The bead and C2 form a L-C filter to attenuate noise from
the input power source. The bead and C1 form another L-C filter that attenuates
noise generated by the SMPS from propagating toward the input power source.
Some designers, in an attempt to use common parts, try to use a power inductor as
the inductive element in the input or output filter. A power inductor is a poor choice
for a high frequency filter even if it has a high SRF. A power inductor is a high Q
component meant to store energy with low loss. A ferrite bead is a low Q part meant
to dissipate energy as heat. The two are not interchangeable.
