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I have some experience with highfrequency circuit analysys. However I am a newbie in PCB design. I am analysing this circuit: http://www.ti.com/lit/ug/spmu365b/spmu365b.pdf (starts on page 36) and regularly see things like "OMIT" for headerpins or components like resistors or so.

e.g.:

  • p41 (6/6): the boxheader(?) on the left.

  • P40 (5/6): R48 on the dev board are two small surfaces with some soldering on it but no component apparently. I can hardly see myself (de)soldering resistors on my new dev board...

Why is this being mentionned? What do the people who made the PCB mean by this?

I mean if this part has to be omitted, why did they even place it on the PCB?

Thx

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Extra/omitted parts on a PCB can be very useful for

a) Having multiple versions of a circuit able to be built with only one PCB

b) Debugging, when I lay out an RF board I often put an omitted 1k SMD resistor from the line finishing near to a ground pad. Invaluable to solder a 50ohm coax to for probing the signal on the line, with good RF integrity and without damaging the line. A JTAG or RJ45 socket may be handy for digital access to a board for debug, but is not needed in production, it's omitted for cost or because it won't fit in the final production case.

c) You may often see a 0 ohm resistor in series with a power line, for monitoring current, or isolating parts of the circuit. These pads may also have a trace under them to short them in the normal case, the trace can be cut to use the component.

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  • \$\begingroup\$ Also sometimes I see omitted 0 ohm resistors that get hand soldered into the device in a multistage signal path, where each stage is tested seperately, and only then all are connected together \$\endgroup\$ – PlasmaHH Jul 11 '16 at 15:48
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    \$\begingroup\$ Other terms which mean the same thing are "Do not load" (DNL) or "Do not populate" (DNP). \$\endgroup\$ – Nick Alexeev Jul 11 '16 at 16:06
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    \$\begingroup\$ Also "DNI" for do not install, or simply "NOLOAD". \$\endgroup\$ – The Photon Jul 11 '16 at 16:09
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    \$\begingroup\$ I have also seen "DNS" for "Do Not Stuff", but I'm not sure how common this one is. \$\endgroup\$ – DerStrom8 Jul 11 '16 at 18:10

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