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TVS diode for the CP2102N USB-to-UART bridge

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voltsandjolts:
At 12Mhz, total waste of time. At 480Mhz, absolutely yes.

tooki:
Just because it’s not absolutely critical doesn’t make it a waste of time. It’s still a good idea to stick to what the standard says!!

As I said: I’ve seen a CP2102N board fail entirely because of bad USB layout. Admittedly it was really bad, but still.

Again: since OP has the ability and knowledge to do it, they should. It takes little effort and reduces the risk of it not working.

voltsandjolts:

--- Quote from: tooki on February 06, 2023, 05:31:28 pm ---it’s not absolutely critical

--- End quote ---

For the few cm of tracks from connector to mcu, it's not critical in any way, shape or form, there is huge margin at 12MHz.
In fact, I'd be interested to see that pcb layout where you say it caused problems, that's quite an achievement!
Seperate DP/DM around different sides of a high power DCDC converter maybe?!

tooki:

--- Quote from: voltsandjolts on February 06, 2023, 05:49:30 pm ---
--- Quote from: tooki on February 06, 2023, 05:31:28 pm ---it’s not absolutely critical

--- End quote ---

For the few cm of tracks from connector to mcu, it's not critical in any way, shape or form, there is huge margin at 12MHz.
In fact, I'd be interested to see that pcb layout where you say it caused problems, that's quite an achievement!
Seperate DP/DM around different sides of a high power DCDC converter maybe?!

--- End quote ---
I don’t have the design files unfortunately, but I do have a few of the nonfunctional boards I could beep out tomorrow.

They were basically the ESP32 Devkit C reference layout, modified to not use 0402 components. (So what’s on it is the ESP32 module, the CP2102N, a 1117 LDO, the two programming transistors, a few diodes, the power LED, and passives.) For reasons unbeknownst to me, the kid doing it didn’t just scoot around the few things that were in the way, but tore up all existing traces and then did them all anew. I remember one of the USB data lines taking a weird stroll around one way, while the other was more direct. His boards simply wouldn’t enumerate. Windows would sometimes make the “new device” sound, but then it would be followed by some error message.

I then took my own shot at the same task (modifying the layout to larger passive footprints), plus extending the USB a few mm to a pin header in lieu of a micro-B port, and it worked flawlessly. I then fully integrated the CP2102N and ESP32 module into the main PCB. It also works perfectly. (I did use impedance control in Altium for the USB data lines on the fully integrated board.)

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