Custom Teensy PCB Boot Loop

F

Festivus

New member
Hey guys! I built a custom Teensy 4.1 PCB and I'm having some issues troubleshooting my board. I don't have the schematic and layout files handy at the moment but if needed I can post them.

Now to my issue. When I plug the board to my pc the red light does not flash indicating any errors however my pc continuously makes a sound for usb device connected every second. When I press the program button once, the red light flashes dimly on for 1 second then off for 1 second, my pc still making the usb device connected sound continuously. When I hold the program button for 15 seconds, the sound on my pc stops and the red light is lit for 15 seconds brightly. My first guess is that maybe the main IC is losing power somehow but I'd like to ask the pros what their opinions are.

Thanks so much for the help in advance!
 
Festivus said:
When I press the program button once, the red light flashes dimly on for 1 second then off for 1 second, my pc still making the usb device connected sound continuously
Click to expand...

Does this dim slow blink happen only once, or does it continue over and over if you don't do anything?

Continuing slow dim red LED blink means you're in bootloader mode and the bootloader is waiting but has not yet heard any USB communication. It's mainly meant to diagnose problems with Teensy used by power-only USB cables which have no wires for D+ and D-.

If you're seeing that blink, and your PC is repeatedly detecting device attach but no device is actually present, perhaps you have one of the USB data lines connected (the one that have 1.5K pullup to indicate device present) and the other not actually connected?
 
Yes, the dim slow blink continues over and over if I leave it be. On my layout the USB port's USB1_DN is connected to USB_OTG1_DN(M8) on the main IC and the USB1_DP to USB_OTG1_DP(L8). I assembled the boards myself and 2 boards exhibit the same behavior so I think I can confidently rule out a manufacturing error on my end. That being said, maybe there was a manufacturing error with the traces. What files would be useful for you to see to help pinpoint this issue?

Thanks so much again.
 
I am realizing now that I didn't take into consideration the impedance of the D+ and D- traces nor did I make sure they were as close in length as possible. Before I go barking up the wrong tree, wanted an opinion on whether this is likely to be the root cause or not.
 
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