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Visitor II
September 10, 2024
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Bypass Capacitors on NUCLEO-H723

  • September 10, 2024
  • 2 replies
  • 1267 views

I am trying to design my own board using the STM32H723ZGT and using the nucleo schematic as a guide. I believed 100nf was typical for the VDD pin bypass capacitors however there is one pin(pin 62) with a 4.7uf capacitor instead. I understand the VBAT and VDDA pins having a different values but why is the C60 bypass capacitor this much bigger bigger? thankyouScreenshot 2024-09-09 201627.png

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    Best answer by STTwo-32

    Hello @gigtrent and welcome to the ST Community :smiling_face_with_smiling_eyes:

    As mentioned on the part 7.4 of the AN5419:

    "All the power supply and ground pins must be properly connected to the power supplies. These connections,
    including pads, tracks and vias should have lowest possible impedance. This is typically achieved with thick track
    widths and, preferably, the use of dedicated power supply planes in multilayer PCBs.
    In addition, each power supply pair should be decoupled with filtering ceramic capacitors (100 nF) and one single
    ceramic capacitor (min. 4.7 μF) connected in parallel. These capacitors need to be placed as close as possible to,
    or below, the appropriate pins on the underside of the PCB. Typical values are 10 nF to 100 nF, but the exact
    values depend on the application needs."

    STTwo32_0-1725958714939.png

    Best Regards.

    STTwo-32

     

    2 replies

    STTwo-32Answer
    Technical Moderator
    September 10, 2024

    Hello @gigtrent and welcome to the ST Community :smiling_face_with_smiling_eyes:

    As mentioned on the part 7.4 of the AN5419:

    "All the power supply and ground pins must be properly connected to the power supplies. These connections,
    including pads, tracks and vias should have lowest possible impedance. This is typically achieved with thick track
    widths and, preferably, the use of dedicated power supply planes in multilayer PCBs.
    In addition, each power supply pair should be decoupled with filtering ceramic capacitors (100 nF) and one single
    ceramic capacitor (min. 4.7 μF) connected in parallel. These capacitors need to be placed as close as possible to,
    or below, the appropriate pins on the underside of the PCB. Typical values are 10 nF to 100 nF, but the exact
    values depend on the application needs."

    STTwo32_0-1725958714939.png

    Best Regards.

    STTwo-32

     

    gigtrentAuthor
    Visitor II
    September 10, 2024

    HI STTwo-32, this is great thankyou I've had a bit of trouble finding the AN for this series this is a massive help. Cheers 

    Technical Moderator
    September 10, 2024

    Hello @gigtrent and welcome to the community.

    Decoupling/Bypass capacitors is HW recommendation and not only restricted to STM32 MCUs but to digital circuits: 

    https://components101.com/articles/decoupling-capacitor-vs-bypass-capacitors-working-and-applications

    https://www.quora.com/What-is-the-purpose-of-using-two-capacitors-a-small-value-electrolytic-and-a-large-ceramic-as-decoupling-bypass-in-power-supplies:

    Does it represent an issue for you?