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I want to add a reset button to the MCU in a PCB that I am trying to design. I came across some SMD buttons, but I wonder what is the difference between them?

enter image description here

One of them has a ground terminal. What is the purpose of that and can you possibly give a usage case for the button with ground terminal?

A normal reset would just require button with 2 pins (AFAIK): enter image description here

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  • \$\begingroup\$ The ground terminal is likely something you'd only need to worry about if switching high frequency signals through the button, or high voltages. I've never seen it before, though, so maybe there's another reason you might want it. \$\endgroup\$
    – Hearth
    Feb 25, 2021 at 16:52
  • \$\begingroup\$ @Hearth well if I have a high freq signal, I attach the pin 1 to one side and pin 2 to other signal, then what is up with the GND pin? is it for having narrow loop area or something? I mean how will it help, if any \$\endgroup\$
    – DEKKER
    Feb 25, 2021 at 17:02
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    \$\begingroup\$ @DEKKER The datasheet writes, "Models with ground terminals are available for protection against static electricity." I take this to mean that they include a tab that allows you to directly ground the metal case (or tie it to some other driven output, I suppose.) \$\endgroup\$
    – jonk
    Feb 25, 2021 at 17:04
  • \$\begingroup\$ @DEKKER Controlled impedance, was what came to mind. \$\endgroup\$
    – Hearth
    Feb 25, 2021 at 17:06
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    \$\begingroup\$ As @jonk says, it allows the static charge from the users finger to go to ground (or chassis depending on how you wire it) instead of into the signal path. \$\endgroup\$
    – Aaron
    Feb 25, 2021 at 17:09

2 Answers 2

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One of them has a ground terminal. What is the purpose of that and can you possibly give a usage case for the button with ground terminal?

I think you might be asking the wrong question. It's usually a good idea to ground metallic parts on the PCB. The question is why is the part on the left supplied without a grounding tab.

enter image description here

Figure 1. The grounding tab has a larger PCB footprint. It adds 1.1 mm (44%) to the footprint (top edge of switch to bottom edge of pad).

I suspect that the tab-less option is provided for very high density designs where the grounding is not required.

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  • \$\begingroup\$ The cheaper switch might be used in plastic enclosed fobs or a mouse (floating mobiles) if designed carefully. \$\endgroup\$ Feb 25, 2021 at 17:25
  • \$\begingroup\$ Haha that was a plot twist...I was wondering the ground pin is waste of space...now I know it is not! thanks \$\endgroup\$
    – DEKKER
    Feb 25, 2021 at 17:31
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It is just for shielding the signals routed to the pins of the actual contacts from ESD.

And it can also an extra mounting pin for better mechanical stress handling.

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