PCB trace

Discussion in 'General Electronics Chat' started by Dritech, Feb 14, 2014.

  1. Dritech

    Thread Starter Well-Known Member

    Sep 21, 2011
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    Hi,

    I am going to connect a capacitor between the positive trace and the ground trace (each trace is 10mm wide). Should I design the PCB as shown in figure 1 or as shown in figure 2?
     
  2. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    If there is no physical reason, such as clearance for another component, that would require the small indents be present on the pcb traces, then use the configuration shown in fig. 2.
     
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  3. MrChips

    Moderator

    Oct 2, 2009
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    Neither of the two.
    A power supply decoupling capacitor doesn't go across the power rails any where you please. It goes between the power and ground pins of the ICs.
     
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  4. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    decoupling?

    Where was that asked about? Is some part of this post missing for me?
     
  5. DerStrom8

    Well-Known Member

    Feb 20, 2011
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    This is correct. Put the cap as close as you possibly can to the pins on the IC, otherwise you can get a lot of interference and the cap will be completely useless.
     
  6. Dritech

    Thread Starter Well-Known Member

    Sep 21, 2011
    756
    5
    Thanks for the replies. The capacitor will be connected 3cm away an H-bridge IC. Should I connected closer to the IC or is 3cm fine? Unfortunately I am a bit restricted because of the IC heatsink.
    Also, apart from distance, which trace is the best option please?
     
  7. DerStrom8

    Well-Known Member

    Feb 20, 2011
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    Usually if you put a cap across the power buses it's for decoupling.

    3cm is quite far, you really want to keep it to a few mm if possible. If you can't have it that close, get it as close as you possibly can. And as mentioned before, if there's no specific reason for the notches in the traces, don't put them there. Use option #2.
     
  8. #12

    Expert

    Nov 30, 2010
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    You can split the capacitance for physical obstructions. The fastest part of the load change can be supplied with a .1 ceramic within a few millimeters of distance and the bulk capacitance can be a few dozen millimeters away.

    ps, do not notch the supply bus.
     
  9. Dritech

    Thread Starter Well-Known Member

    Sep 21, 2011
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    Is it practical to solder the capacitors on the bottom side of the PCB (with the pin pads of the H-bridge supply) ?
     
  10. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    Close for an op amp or logic IC. I don't see the need to be so close on an H-Bridge. It is just a block of 4 independent MOSFETS in one package. As long as the gates are connected correctly, I have never seen a need for a ceramic cap on an H-Bridge chip. Just make your power traces wide enough. I don't put a cap next to a discrete mosfet, why on an HBridge?
     
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