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On the ATmega32U4 MCU there are several pins related to USB:

  • VBUS
  • D+
  • D-
  • UCAP
  • UGND
  • UVCC

In the datasheet and in almost all reference schematics I find on the Internet, it's explained how to connect those pins when you need the USB.

On my board, instead, I don't need the USB at all. Hence, I want to understand how to connect those pins.

I'm not sure if I can just leave them floating or else.

Mark
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2 Answers2

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The datasheet does have that information.

You can make a self-powered USB device as per the datasheet diagrams and imagine the USB cable is unplugged, which gives enough information how the pins should be connected without USB connection.

Justme
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On my board, instead, I don't need the USB at all. Hence, I want to understand how to connect those pins.

Grab a schematic that uses the USB interface like this: -

enter image description here

And ask yourself what connectivity is important if there isn't anything plugged into the USB connector. You'd end up with this: -

enter image description here

Schematic image taken from here.

So, should VBUS be connected to Vcc - you can always double check that in the data sheet and, is it any great hardship to make that connection anyway? What about UVCC and UGND - well, is it really any problem to connect them to Vcc and GND

Andy aka
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  • It's not a problem. But I'm trying to understand, not to guess... For example, the capacitor on UCAP may be mandatory because it's the output of the internal regulator. I cannot know if omitting it may lead to some issues. – Mark Feb 07 '22 at 14:45
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    @Mark then you should thoroughly read the data sheet from front to back and double check everything. – Andy aka Feb 07 '22 at 14:50