Twitter Quiz – PCB routing


PCB

Many IC have more than one VCC . All we know why filtering capacitors are add to VCC power supply, but if we want to spare capacitor and use one capacitor for two VCC signals on the VCC how is the correct way to route it like on the left hand side of the picture or like on the right hand side?

Please answer on Twitter you have time until Monday🙂

6 Comments (+add yours?)

  1. LinuxUser
    Oct 18, 2015 @ 08:58:55

    I don’t have twitter account, so I will answer here.

    I think right option is more safe, as long as Vcc’s are connected by low-resistance tracks.

    Rationale: multi-Vcc ICs tend to have tight requirements on voltage differences between Vcc’s. Right scheme is better in this regard. Making strong currents flowing via internal IC interconnects is a bad idea to my taste.

    Reply

  2. H.Trickler
    Oct 18, 2015 @ 14:18:15

    The left drawing has 2 ‘impedances/resistors’ which are higher than the one at the right, which is lower because it can also occupy the spacing between both lines of left diagram. Therefore right is better.

    Reply

    • LinuxUser
      Oct 18, 2015 @ 17:31:16

      Objection: ICs have Vcc’s interconnected internally. So formally on left side you have 2 parallel tracks resistances and on right side you have one track resistance. Left side is better in this regard if we assume identical tracks. But I can see other considerations…

      Reply

  3. Bob Wettermann
    Oct 19, 2015 @ 13:03:54

    “I think right option is more safe, as long as Vcc’s are connected by low-resistance tracks.”

    Reply

  4. new
    Oct 19, 2015 @ 18:20:17

    This is not a valid question, since from the point of view is from the schematic editor and not the PCB editor. In other words the schematic does not care how you draw it, it just sees a connection between two pins. Two pins by the way that are not close to each other on the PCB. Spend the extra pennies and put in the other cap.

    Reply

  5. bib
    Oct 21, 2015 @ 23:42:59

    Hi all,

    Schematics – as it is drawn – has nothing to do with PCB physical implementation. Nevertheless assuming the +VCC rail is embedded inside the chip die, personally i tend to route the two pins together with one track to C 100nF –> 0V instead of routing two tracks. So the schematic on the right should be the right choice in respect of PCB implementation.

    Reply

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