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Possibly hardware issue with USB

Question asked by Yuriy Dovgalyuk on Jan 19, 2015
Latest reply on Jul 27, 2015 by Daniel Rosales

Hi all

 

I need a help regarding troubleshooting of the USB issue.

I made 2 custom PCBs (MK22FN1M0VLH12), both have USB connector, routing is almost the same. Both PCBs are working fine, the firmware is absolutely the same inside both MCUs.

BUT, as soon as I connect a USB cable to PCB A, it stops working, generates hard fault (could be bus or usage fault), while PCB B is working fine and USB functionality works as expected.

 

Measures taken to solve the issue:

  • At the beginning I put 51Ohms terminator resistors on both PCBs. In this stage PCB A does not work, PCB B works fine.
  • Then I changed resistors to 33Ohms (as recommended) on PCB A, did not help.
  • Then I tried to remove resistors and short cut on PCB A, did not help, so I moved back to 33 Ohms.
  • Then I enabled MPU on PCB A and saw generates MPU errors, this is just an additional information

 

I attached pictures that show how PCBs are routed.

I need some ideas what to try more? Should I add pull-down 15kOhm resistors to data lines?

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