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I have some questions about the connection and its external components for the SMPS step-down converter of the MCU.

The microcontroller I'm using is a STM32H745IIT6. On the datasheet I found this schematic and these indications for the components:

enter image description here

Question 1: The ESR is indicated for capacitors, but I can't find this information in the datasheets of any ceramic capacitors, is it because the ESR of ceramics cap is so low that it is not even indicated? How can I tell if the capacitors I have chosen are good?

I was thinking of using these: 885012208094 for 4.7uF and 885012214001 for 10uF.

Question 2: The DC resistance is indicated for the inductor, but is this a maximum value or must it be that resistance?

Just to understand, between these two inductances: 74479276222C and 74479288222, which one is better?

Question 3: regarding the capacitors on VCAP and VDDLDO, I still follow the pattern I see a few pages before the datasheet? This:

enter image description here

To conclude this is the circuit I was thinking of doing, could it work well?

enter image description here

SamGibson
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Federico Massimi
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  • A little bit about cermaic caps and ESR here: https://electronics.stackexchange.com/questions/13447/how-is-esr-specified-on-ceramic-capacitors – DiBosco Apr 17 '23 at 15:41
  • Even linear regs can become unstable with the wrong type of caps/unsuitable ESRs. If the datsheet is specifying speicfic ESRs you are probably best with trying to find a cap that as closely as possible fits the ESR. The datsheet snippet you've shown has non polarised caps on the schematic though. Is there a dev board for this part or a family memeber you could look at and get a better idea from? – DiBosco Apr 17 '23 at 15:47
  • There is no evaluation board for my chip, but there is one very similar, but it uses different values for the capacitors than those recommended in the datasheet, I think it's because they use the same PCB for other MCUs too. This is the link, but it didn't help me (indeed maybe it just caused me even more confusion). https://www.st.com/content/st_com/en/products/evaluation-tools/product-evaluation-tools/mcu-mpu-eval-tools/stm32-mcu-mpu-eval-tools/stm32-nucleo-boards/nucleo-h745zi-q.html#cad-resources – Federico Massimi Apr 17 '23 at 17:19
  • @FedericoMassimi - Hi, Please remember the [site rule](/help/referencing) which requires that when a post includes content (e.g. text, image, photo etc.) copied from elsewhere, that copied content must be correctly referenced. The source webpage or PDF etc. should be linked as a minimum (references for books / articles should include title, author(s), publisher, edition, page numbers etc.). In order to help you, I found (what I believe to be) the source PDF link in this case and added it for you. For the future, please remember it's your responsibility to do that :) Thanks. – SamGibson Apr 17 '23 at 18:11
  • @SamGibson: OK, thank you – Federico Massimi Apr 18 '23 at 07:14

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