JTAG-SMT3-NC Module can't be deteced

[fbergmann]

Hi All,

im new to this forum.

I just finished my first project with a Digilent SMT3 USB-to JTAG/UART board. Unfortunately the module is not properly detected in Windows (Code43).

 

it says "unknown USB-Device (Error when reading a device description)". Do I need any special drivers? I already tested three of my designed boards as well as three different USB cables. All USB certified USB-A to USB Micro-B.
 

Neither Digilent Adept 2 Software nor Vivado 2022.1 can detect the SMT3 module.

Attached please find the Schematics of my board.

Did I miss anything?
USB_P and USB_N are routed 90Ohms differential.

 

thanks a lot,

~F

 

 

Edited January 22, 2023 by fbergmann

[JColvin]

Hi @fbergmann,

I asked the design engineer most familiar with the SMT modules and they let me know that D14 is the most likely culprit for your problem. That particular part has too high of a capacitance value (30 pF according to the datasheet) for USB data lines. They also linked me an application note on this topic: https://assets.nexperia.com/documents/application-note/AN10753.pdf they had on hand since they've seen this issue in other designs wanting to use some extra diodes for ESD protection.

Thank you,
JColvin

[fbergmann]

Hi!
Thank you so much for that suggestion. it is now working like intended.