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ANP028b; 2016-04-07, MHb Page 1 of 7
APPLICATI ON NO TE
The world's first peak current load SMD ferrite
The Multilayer Power Suppression Bead
ANP028 BY MARKUS HOLZBRECHER
1. Background _________________________________________________
A Chip Bead Ferrite has inductance that is established using a screen printing process. This is optimised for
as high as possible losses for use as filter. Therefore, it consists of a nickel-zinc-ferrite mixture and a very fine
superimposed inner silver layer with thickness of a few micrometres. This structure makes the classic SMD
ferrite more vulnerable for current spikes above the maximum rated current load and in special cases results
in degenerative or also immediate destruction of the component.
1.1. Application
A typical application is shown in Figure 1. The multilayer ferrite is used as longitudinal filter at the input of the
circuit. Due to the low on-resistance of the capacitor, a very high pulse current flows for a short time at switch-
on. This pulse current temporarily loads the SMD ferrite with a multiple of the current that is many times above
the maximum specified rated current.
In this example, the optimised multilayer ferrite, that is designated by Würth Elektronik eiSos as Multilayer
Power Suppression Bead (MPSB), has impedance of 600 ohms for a maximum permissible rated current load
of 2.1 A. The one-time current peak in this constellation has a peak value of approx. 19 A and has an overall
pulse length of 0.8 ms until it has been reduced to the rated current of the circuit.
Figure 1: Application with peak current at switch-on (5 A / DIV | 100 µs / DIV)
It generally applies for the SMD ferrites that the maximum rated current also defines the maximum current
amplitude for temporary load. However, using the new WE-MPSB series with pulse load, multilayer ferrites are
now available that consider the peak current in the data sheet.
