How should select Ferrite bead at ADC pin of STM32F4

Thread Starter

mishra87

Joined Jan 17, 2016
554
Hi All,

How do i select ferrite bead value on MCU STM32F4 series.?
What is value and other parameters needs to be taken care into consideration.?

How do i decouple analog and digital ground on PCB board.?

Regards,
 

OBW0549

Joined Mar 2, 2015
3,015
I would never use ferrite beads on the ADC inputs to a microcontroller, for one simple reason: I never, never, NEVER connect any microcontroller pin, input or output, analog or digital, directly to the outside world (i.e., off-board). Doing so invites all manner of trouble, in the form of susceptibility to external interference as well as damage from ESD. In the case of ADC inputs, I always precede these by a buffer amplifier of some sort, at a minimum, as well as whatever input protection and filtering is appropriate for the operating environment. But ferrite beads? Never.

Ferrite beads are most appropriate for the power sections of circuits. Read the following:

https://forum.allaboutcircuits.com/threads/selection-of-ferrite-bead-value.39412/
https://www.allaboutcircuits.com/industry-articles/ferrite-beads-demystified/
https://www.allaboutcircuits.com/technical-articles/clean-power-for-every-ic-part-3-understanding-ferrite-beads/
https://www.allaboutcircuits.com/technical-articles/choosing-and-using-ferrite-beads/
 

Thread Starter

mishra87

Joined Jan 17, 2016
554
I think, there was some misunderstanding of my data.

My intention was to ask ferrite on VDDA pin of MCU.
Is there ferrite bead needed on Analog supply of MCU.

If yes, what would be selection criteria.

As most for MCU manufacture recommend this.
Regards,
 

MrChips

Joined Oct 2, 2009
19,383
What are you using to power your circuit?

Ferrite beads are not required in most situations.
0.1uF capacitors across the power and ground are essential.
 

Thread Starter

mishra87

Joined Jan 17, 2016
554
What are you using to power your circuit?

Ferrite beads are not required in most situations.
0.1uF capacitors across the power and ground are essential.
Power circuit will have 24 to 5V STEP DOWN CONVERTER AND 5 TO 3.3V LDO

some of analog inputs are coming from out from PCB board

Regards,
 

Thread Starter

mishra87

Joined Jan 17, 2016
554
Hi All,

Could any body explain below graph from wurth Electronik and how do I select ferrite bead for any particular application.

1. Ferrite Beads WE-CBF 0402 SMD Bead 100MHz 20Ohm 300mA if I want to understand in one line how do I understand.

upload_2019-8-3_12-43-25.png

Regards
 
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