Create a part of DUE for my project

Hello to you all,

I have a project which involves an Arduino DUE. Except the DUE there are two main parts.
A LCD display shield and an IC from TI which communicates through SPI and uses 6 digital pins.

So I want to make a pcb where I have everything I need except the LCD shield which will remain as a shield to my new board.

I'm writing this thread because I want to be sure I don't leave out anything important for the correct operation of the SAM3X8E processor.

I tested my DUE and I can bootload my code through native usb so I'll include that to my pcb but I won't have the programming port and the microcontroller DUE has.

So I will include the native usb port (usb AB), the crystals, the decoupling capacitors, spi, jtag, reset and the pins my LCD display is using plus 6 digital pins for my chip.

Some of the circuits I leave out are the programming usb port (usb B), the atmega mc, i2c, power supply and the circuit which switches power supply between usb and power supply.

I know I ask much but if anyone of you sees I forget to include something so my processor works would be very helpful.

Thank you in advance,
Spiros

I will probably want to do something similar, it really does seem that it's as simple as you suggest. Without a complete circuit diagram I couldn't guess if it will work, but in principle I don't think you've missed anything.

So I have an update,
I did the above curcuit and have two major issues…
When I connect my usb all the voltage supply goes up to 3.8V.
I just followed the wiring diagram from Arduino and it connects usb power supply to pin39 (xusb).

Even if this doesn’t damage the microcontroller my laptop doesn’t recognise any ports when I plug my pcb so I can’t really program it.

Can anyone give any advise on how I can deal with this?

I'd really need to see the diagram and your layout, it sounds like something is connected incorrectly. What USB voltage do you see before and after connecting?

My diagram is a bit messy but I'll post it later on.
As far as the connections I followed the due wiring diagram.
Before USB connection I have 3.3V that I produce from a TI regulator.
When I plug it to my PC I get 3.8V.

Is the whole thing powered via the USB connection or do you have another supply? If you have another supply, is it fully isolated from earth?

Here is the DUE's part.

I have another supply for my circuit, I only want native USB to program it.

Here is the wiring for my USB

I connect xusb, D+ and D- to my sam3x8e chip.
The xusb has 3.8V.

Oh, XUSB is 3.8V. Is the 3v3 line still 3v3 when you plug in (is it before you do?)
The diagram is a little difficult to read, I can't spot any issues with it tho.

The USB supply is being pulled down by something, if the 3v3 is also going to 3v8 then you have a short between them. If the 3v3 is at some other value then it's short to something else, or you are somehow drawing too much current from the USB and it's dropping.

Here is the pdf with the DUE's schematic which I took into account.

In my first post I mention which circuits I used.

When I plug the usb the 3v3 becomes 3.8V.
I haven't located any shortcircuits but I believe this could happen inside the sam3x8e.

What resistance do you see between 3v3 and XUSB (with all power disconnected)?
What voltage so you see at XUSB before you plug in the USB?
Another option is to isolate pin 39 if possible.