Ferrite bead networks – it takes multiple beads to tango
Ferrite beads come in groups – if your circuit needs one, it usually doesn‘t take long until a regulator makes you add another. Laird now provides a resistor array-like solution for the ferrite bead problem.
For those of you new to the concept: a ferrite bean is a resistor which rejects high frequencies. Look at the impendance chart shown, which we took from the data sheet.
…the resistance of a ferrite bead increases with frequency
It takes but one look at to understand what a ferrite bead is good for: place it in series with a component to eliminate high-frequency radiation. Popular candidates would be switching regulators, but also a variety of other chips such as amplifiers which work by modulating carriers.
Laird’s part differs from the competition in that it combines four ferrite beads in a 1206 housing. This makes the part ideally suited for controlling outputs. Put it next to a chip which needs to be disciplined, and don’t worry about pick and place costs.
From a technical point of view, the part is a classic ferrite bead. Its maximum current current is 300 mA continuous, its resistance in the DC range is around 0.2 ohms.
The main issue is that its impendance starts to raise in the range of more than 10 MHz. This makes the part poorly suited to small amplifiers, whose carrier wave is in the range of 100 kHz or so.
Other than that, the part is a total buy. The figure shows the pricing, which is very much in line with four single ferrite beads. Furthermore, using dedicated ferrite beads requires more space on the PCB.
Keep repairability in mind when using this part. While the component is on the market since 2004, one never knows when it might be discontinued. Furthermore, if your equipment is used in areas with limited parts availability, saving maintainers the hassle of finding a ferrite bead array might be appreciated.