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I want to design a circuit using ws2811 on page 5 of the datasheet It says "To prevent the reflection and hot-swap protection, we suggest to connect a 33ohm resistor at the data input or output port for impedance."

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But on modules and boards on the market I don't see these 33ohm resistors, How important is it to add these? In what situations may it be neccessary?

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But on modules and boards on the market I don't see these 33ohm resistors, How important is it to add these? In what situations may it be neccessary?

If the chips/modules/boards (you refer to) cannot be hot swapped AND the data transmission distance between them is small (for 400 kbps) then you can probably avoid using them. When they talk about "reflection" they are referring to transmission line reflections upsetting the digital data passed between them - it's necessary to "quench" reflections or you get corrupted data.

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  • \$\begingroup\$ So do you recommend adding them(They might be a connected by long wires)? Is there any possible drawbacks if they are in the circuit? \$\endgroup\$
    – ahmadx87
    Dec 22 '15 at 18:28
  • \$\begingroup\$ Well, it's the data sheet that recommends them and when a DS does this you have to come up with a pretty good reason not to do it so, yes, if you have long wires you might get data corruptions without them. Of course that may be only once every so often but could still be annoying. \$\endgroup\$
    – Andy aka
    Dec 22 '15 at 18:35

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