I found the diagram below online while looking for information on the orientation of a choke I intend to use in an LVDS application. Does the orientation of the choke matter? The part I intend to use is the 744233121 by Wurth Elektronik. The chokes will be located right before the FPC connector on my PCB to which I connect the off-PCB display module.

enter image description here

  • 2
    \$\begingroup\$ What do you mean by "orientation"? I guess what matters is that the dots are on the same side. \$\endgroup\$ – Dmitry Grigoryev Apr 20 '18 at 10:56
  • \$\begingroup\$ @DmitryGrigoryev the dots pointing towards the LVDS drivers in (c), or pointing towards "off-board" \$\endgroup\$ – b20000 Apr 20 '18 at 13:07
  • \$\begingroup\$ The dots which represent mutual inductance polarity. Quite obviously, the mutual inductance should work against common mode currents. \$\endgroup\$ – Dmitry Grigoryev Apr 20 '18 at 13:16
  • \$\begingroup\$ @DmitryGrigoryev so is the orientation of the component important or not? \$\endgroup\$ – b20000 Apr 20 '18 at 14:53

The dots show the orientation of the two coils relative to each other. When the dots are on the same side, this means that the windings are negatively coupled. This is always the case for a common-mode choke (see this article for details).

The coils are just pieces of wire wound onto a core; the current behaves identically when flowing through them in either direction. (The only thing that matters is whether the currents in the two coils flow in the same or in the opposite direction.)

These dots are shown in the schematic symbol, but are not marked anywhere on the actual device, and the datasheet does not specify how to detect the orientation:

Würth 744233121        Coilcraft 1206USB

Some datasheets will explicitly say this:

Murata DLW31S

The orientation does not matter, and even if you wanted to, you would not be able to choose any specific orientation.

  • \$\begingroup\$ Once I had a customer who soldered all CM chokes in 90-degree position, on USB traces. They were complaining that our product doesn't work ... :-) \$\endgroup\$ – Ale..chenski May 13 '18 at 5:42

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