How would you design in CMC's with a 0504 (1210 metric) 4-lead package to allow for a no populate (do not pop, DNP,DNI) solution? I am thinking 0402 0ohm (zero ohm) resistor but cannot picture the PCB layout?

Specifically, this is for USB data lines and the CMC's may be used to reduce radiated EMI.

Edit 7/9/19 Would this footprint setup work okay? 4-pad CMC with two 0402 resistors in series. enter image description here


In these situations for prototyping I do something like this:

enter image description here

You cut the traces on the PCB if you need to install the choke. That way you don't impedance problems from soldering wires. The problem with this setup is once you cut the PCB traces, you can't go back. Another way to do this would be to put 0 ohm resistors in series with the choke. Or you could use 0 ohm resistors if you select them the same size as the choke gap.

  • \$\begingroup\$ You can always go back with cut traces. With a suitable ECN and solder bridge \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Jul 8 '19 at 17:34
  • \$\begingroup\$ In my case the thermal EMF would not be the same, when I cut, it's one way. \$\endgroup\$ – Voltage Spike Jul 8 '19 at 17:38
  • \$\begingroup\$ In our shops where I worked, it was neat but bridgeable. It is always a better idea to include CM chokes for USB. I have seen too many data errors without this using Towers to Arduino on floating supplies etc. Due to SMPS CM noise. \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Jul 8 '19 at 17:53
  • \$\begingroup\$ see edit, how does that look? \$\endgroup\$ – RuggedEngie Jul 9 '19 at 18:28
  • 1
    \$\begingroup\$ @RuggedEngie Looks great to me... \$\endgroup\$ – Voltage Spike Jul 9 '19 at 18:30

It would be a dual pad layout joined for either SMD CM choke or any SMD 0R parts or fixed R parts depending on design.

The design would be controlled impedance for USB2 (100MHz) or USB 3.


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