brownt
Member level 3
Hi,
I am using some Murata ferrite beads for EMI suppression above 30MHz..These Murata ferrite beads in any particular model are available in various impedances @100MHz. For example 10 - 1000 ohms. I don't understand why anything other than the maximum impedance type would be chosen. Why are there so many impedance types?
There are so many models available that I am really not sure what to get. The attached picture shows six graphs for six devices. The DC resistance and current capability is about the same for all of them, and will suffice for my application.There are three different physical sizes, 15, 18 & 21, and any of those size are OK for me. I need one bead on the VCC line of the 64MHz MCU, and perhaps also on the 4MHz SPI line, for the clock, data in and also data out, I guess.
It seems to me that if I want to limit radiated emissions at 30MHz+ then the best choice is BLM21RK102N1, because its resistive area starts lower than any of the others, at about 7MHz (where X crosses R). But if it is that simple then I don't know why there are so many choices and why anyone would ever choose anything else.
It seems that a device with a resistive curve starting above 30MHz is no good and so none of the devices on the right are satisfactory. But again with everything commercial needing EMI certification for radiating emissions above 30MHz, I don't know why there are so many options above 30MHz.
appreciate any information. thanks.
I am using some Murata ferrite beads for EMI suppression above 30MHz..These Murata ferrite beads in any particular model are available in various impedances @100MHz. For example 10 - 1000 ohms. I don't understand why anything other than the maximum impedance type would be chosen. Why are there so many impedance types?
There are so many models available that I am really not sure what to get. The attached picture shows six graphs for six devices. The DC resistance and current capability is about the same for all of them, and will suffice for my application.There are three different physical sizes, 15, 18 & 21, and any of those size are OK for me. I need one bead on the VCC line of the 64MHz MCU, and perhaps also on the 4MHz SPI line, for the clock, data in and also data out, I guess.
It seems to me that if I want to limit radiated emissions at 30MHz+ then the best choice is BLM21RK102N1, because its resistive area starts lower than any of the others, at about 7MHz (where X crosses R). But if it is that simple then I don't know why there are so many choices and why anyone would ever choose anything else.
It seems that a device with a resistive curve starting above 30MHz is no good and so none of the devices on the right are satisfactory. But again with everything commercial needing EMI certification for radiating emissions above 30MHz, I don't know why there are so many options above 30MHz.
appreciate any information. thanks.
