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I am using CP2102N-A02-GQFN24 on my custom PCB to program my ESP32 board. I am not able to see any COM port on my Windows 10 PC. I can connect to an off the shelf CP2102N-A02-GQFN28 USB UART bridge board to my computer. So I think that rules out driver issue then I am not really sure what else could be an issue. I was saw numerous people commenting on putting a 1-10uF cap on EN line of ESP32 to fix the timing issue or EN & IO0 line which is connected to RTS and DTR on CP2102 but that didn't help either. I can program my ESP32 if I connect COTS UART bridge board directly to ESP32 EN,IO0,Rx & Tx lines. Most of my schematics is similar to ESP32 Wroom Dev board which you can find schematics in this link except I am using CP2102 24 pin package. I am not using buttons for manual programming but I am using NPN transistors (SS8050-G) for automatic bootloading. I have attached screenshot of my schematics. I have also attached timing snapshot from my OScope. In one snapshot DTR is CH1 & RTS is CH2 and in another snapshot IO0 is CH2 & EN is CH1.

Screenshot from OSCOPE CH1 is DTR & CH2 is RTS Screenshot where CH1 is EN & CH2 is IO0 enter image description here enter image description here enter image description here enter image description here

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  • \$\begingroup\$ Perhaps the CP2102 driver is out of date. \$\endgroup\$
    – tlfong01
    Commented Apr 3, 2022 at 6:29
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    \$\begingroup\$ If the cp2102 is qfn - check every joint - they may look soldered but sometimes they’re not. Use a multimeter to measure the substrate diode on each pin. Double check you got the usb data polarity correct. Been bitten by that before! Basically double check every connection. Assume nothing! \$\endgroup\$
    – Kartman
    Commented Apr 3, 2022 at 7:31
  • \$\begingroup\$ @Kartman good point but I don't know if all 12 boards behave the same way. May be PCB assembly house did a bad job on all of them. Polarity seems to be correct. I thinking more on the lines of RC timing not getting satisfied. I found out that I am missing VREGIN decoupling caps on CP2102 so I have put a jumper to a breadboard where I have 10uF & 0.1uF caps. I did the same for pull resistor of EN & decoupling caps on EN line. In this way I can quickly change the caps value in order to satisfy RC timing but none of it helps. Main issue is that COM port is not detected at all on my computer \$\endgroup\$
    – rtgb
    Commented Apr 3, 2022 at 16:14
  • \$\begingroup\$ @tlfong01 I can program my ESP32 via off the shelf USB to UART bridge which has CP2012 28 pin package. I am using one in this link. digikey.com/en/products/detail/silicon-labs/CP2102N-MINIEK/… \$\endgroup\$
    – rtgb
    Commented Apr 3, 2022 at 16:19
  • \$\begingroup\$ Why did you add a common mode choke to the USB signals? Have you tried removing the choke to see if that is causing your issue? Measure the complete usb signal path with a multimeter from the ‘A’ connector all the way to the cp2102 qfn pad.’seems ok’ is not good enough. Compare with the usb-serial board that works. Be 100% sure your usb connections are correct. Measure voltages. Rule out the simple stuff. \$\endgroup\$
    – Kartman
    Commented Apr 4, 2022 at 1:58

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@Kartman I got it fixed. My U6 chip (ESD TVS diodes) are 4CH chip so it needed to be connected to CP2102 differently. So I modified my traces by cutting the traces coming out from U6 pin 6 & pin 7. After that it is working properly. Did a silly mistake while drawing schematics. enter image description here

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  • \$\begingroup\$ rtgb - Hi, Thanks for coming back with the solution to your question. (a) Please remove that 1st short sentence addressed to a user, and write it as a comment to that user, below their comment. Those notifications only work in comments, not in answers. (b) To effectively mark the topic as solved, please "accept" your answer (click the "tick mark" next to your answer, to turn it green). Since you must wait 48 hours after you asked the question before you can accept your own answer, please accept it after 04:10 UTC tomorrow. Thanks. \$\endgroup\$
    – SamGibson
    Commented Apr 4, 2022 at 19:27

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