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Powering Up the ADC

Asraful
Associate III

‎2024-10-23 05:09 AM

Currently I am Trying to make a custom board for a project now I have done all the decoupling things for the VDD pins however I have to give power supply to the VDDA pin and now I am having some trouble since I am not that expert in hardware. I need few suggestions as for ferrite bead how should I calculate the value needed for that particular board/mcu and I also learned from senior a RLC filter also can do the job perfectly now can someone please suggest me with the guidelines what resources could I follow to learn this things so that I can developed stm32 based board by my self specially this ADC power supply filtering part. I am currently working with STM32F411CEU6
Thanks in Advance. 

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CYANG.1
ST Employee

‎2024-10-27 08:08 PM

Hi, when you want to choose a suitable bead, first you need to know what noise source on your board is. Mainly the noise is from high frequency parts on your board. After you know the noise source and the frequency of this noise, you can select beads with this noise frequency. Normally there is an impedance-frequency curve diagram in datasheet of bead, the corresponding frequency of peak of the curve is the point that the bead can filter the noise best. You can choose suitable bead according to this way.
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Asraful
Associate III
In response to CYANG.1

‎2024-10-27 08:11 PM - edited ‎2024-10-27 08:12 PM

What could be the general noise source the MCU or the LDO? Additionally, where can I learn about it or check it which components are making noises. I know that LDO have some ripples and we have to take care of that and what else I have to consider 

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CYANG.1
ST Employee
In response to Asraful

‎2024-10-27 08:20 PM

Hi,

As I said, mainly the noise is from high frequency part, for example, if there is SDRAM with 100MHz clock on your board, you may pay attention to the 100MHz noise on your board.

Sometime the noise is from the high driver interface, for example, if you run SPI on 20MHz but the signal integrity on the board is not good, the signal will spread its energy, and it would be a noise source.

LDO is a linear part, so it would not spread noise. if there is a DC-DC on the board, we need to take care of its switching frequency as it would be a noise source.

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