I am trying to design a PCB based around the STM32F446RE microcontroller. I looked at the schematic provided by ST for their Nucleo-64 board, and physical placement of the ferrite bead on the board.
The ferrite bead they use is a Taitec FCM1608KF-601T05. Which is placed on the VDDA line (pin 13). They do not have a ferrite bead anywhere else.
I have seen a few designs done by others, and they seem to place the ferrite bead at the input side of the their 5V linear regulator.
In other words, ST seems to concerned primarily with noise coupling on to analogue measurements and have placed the bead after the 3.3V regulator to the MCU.
Other designs seem to be concerned about noise getting into the overall circuit.
- What are the pros and cons of each approach?
- I am considering putting my ferrite bead at the input stage to the 5V regulator, with the thinking I can filter out at everything right at the beginning - but get a feeling that this may introduce other issues.
The ferrite bead I would be using is Würth Elektronik 74279265 which has better DC resistance and impedance characteristics over a wider frequency range.