4
FERRITE MATERIAL COMPARISON
LF, 28, HF Material Impedance vs Frequency ( 300 KHz - 2 GHz )
Frequency ( MHz )
Impedance ( Z ) in Ohms ( Ω )
0.3
0.5 1
5
10 50 100 500 1000
2000
Impedance Materials for Cable & Wiring Harness Cores
LF Low Frequency
28 Broadband High Performance
HF High Frequency
LF
28
HF
· Select the appropriate ferrite material for the EMI frequency range to be attenuated (refer to cable core material impedance vs.
frequency chart above).
· Ferrite material composition affects core performance most. High performance material is best. Cheap, low performance materials
require the use of larger, heavier cores.
· Shape (design) and mass of the ferrite core signicantly affect impedance.
· Don’t over size. Use high performance ferrite material and select the smallest core that will do the job. High performance material allows
the use of smaller, lighter and lower cost cores.
· Select a ferrite core that ts over the cable’s outside dimensions. Core should slide easily over the cable during installation.
· When possible, install a cable core over wires in a common-mode conguration (out and back lines inside the same ferrite cable
core). A differential cable pair inside the same core will make the ferrite core a common mode choke that is not susceptible to
saturation from very high currents.
· Install the ferrite core near the noise source
· Additional turns through a core will provide multiple amounts of peak impedance.
Example: Two wire turns provide 4 times the impedance of one turn (pass through) the ferrite core. Also, with each added turn, the peak
impedance shifts to a slightly lower frequency.
· Two piece split cores are available. One-piece cylindrical or at ribbon ferrite core shapes are usually preferable but, split cores can be
used in applications where cores cannot slide over cable ends and connectors. Some split cores are available with snap-on plastic
cases or metal clips.
· Side by side impedance testing of ferrite cores is the best way to compare performance of different cores.
Ferrite core impedance measurement equipment and test methods are not standardized in the industry. Every ferrite company has
their own test methods. Catalog (web site) impedance data cannot be accurately compared.
DESIGN & SELECTION “RULES OF THUMB”
Optimized, high performance, low cost custom part designs are available.
