[Cryptech Tech] USB interface

[Peter Stuge]

Pavel Shatov wrote:
> Ideally I'd prefer Peter to provide me with a PDF with a piece of 
> schematics he wants added, as he suggested earlier, so that I can just 
> copy it into KiCAD project.

Attached is my proposal schematic, please review it.

For reference, the SAMD11 datasheet is (currently) here:
https://ww1.microchip.com/downloads/en/DeviceDoc/Atmel-42363-SAM-D11_Datasheet.pdf


I also need some feedback on the power supply:

The rev03 FTDI chips are bus-powered, so when a rev03 board is connected
to a PC the PC always sees a USB device, even if the rev03 board is
not currently powered through the 18V supply.

On rev03, PCs can only try to use a heuristic with the RPC protocol to
guess if the board is running/available or not.


This proposed USB interface is self-powered, by VCCO_3V3, so when this
interface is connected to a PC the USB device comes and goes on the PC
as the 18V supply is connected and disconnected from the rev04 board.


Is that change desirable?

I hope yes, because USB is really not a static connection, but please
share your thoughts.

If the change is unacceptable then I'll add a voltage regulator and
probably level shifters in a new revision.


Thanks a lot!

//Peter
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