• State Resolved
  • Locked Locked
  • Replies 4 replies
  • Answers 1 answer
  • Subscribers 83 subscribers
  • Views 312 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TMS320F28377D: Decoupling capacitance

sravani datla
Prodigy 100 points
Part Number: TMS320F28377D

Hi,

It is mentioned in the data sheet that a total decoupling capacitance for 1.2V supply should be a minimum of 20uF. As i want to operate cpu at frequency of around 200MHz the decoupling capacitors should be distributive. So if i have to use 0.1uF capacitors, do i have to place 200 of them in parallel? 

  • 0
    Guru 30330 points
    Hi Sravani,

    No. You do not need to put 200 capacitors. You can just evenly divide the 20uF across the number of caps. i.e. if you are using the 176pin package, you can use ten 2uF caps at each pin (2.2uF would also work).

    Regards,
    Mark
  • 0 in reply to Mark Labbato
    Prodigy 100 points

    Hi Mark,

    Thanks for your response. As we are operating at hundreds of MHz, decoupling capacitors should have low ESL, the problem i am thinking with 2.2uF is that it will have high ESL value compared to 0.1uF and it would be more than allowable inductance value.

    Also can i get 1.2V TMS320F28377D core supply current graph? Thanks in advance

  • 0 in reply to sravani datla
    Guru 30330 points
    Sravni,

    ESR/ESL are primarily influenced by package size and how they are connected to the plane (there is information available online with suggestions for optimal via placement). If the body sizes of the 2.2uF available are too large you can also place a smaller body size 0.1uF capacitor in parallel. Also note you can use a power plane to provide additional capacitance for the supply to draw from, most high frequency current will be supplied by the power plane rather than the discrete capacitors due to the ESL of the package and PCB VIAs as you have noted.

    If that still doesn't satisfy your concern, we have seen implementations with a single Bulk cap of 20uF on the plane, with only the small body size 0.1uF caps placed at each pin.

    Can you clarify your request of the supply current graph?

    -Mark
  • 0 in reply to Mark Labbato
    Prodigy 100 points

    Hi Mark,

         Thanks alot for clarifying my issue. I just want to check how the current profile will be from 1.2 V source when the microcontroller is operating. Just for a better understanding.