I'm working in a proyect that requires that all external connections (in my case, everything related to the USB) to be isolated from the rest of the circuit.

I came up with this circuit using the ADUM141E to isolate the CP2102(usb-uart converter) with the ESP32 and all the circuit required to auto-program it.

enter image description here

And the CP2102 circuit is:

enter image description here

The problem with this circuit is that when I try to program the ESP32, the PC recognise the CP2102 but can't communicate with the uC. This is the error that appears:

A fatal error occurred: Failed to connect to ESP32: Timed out waiting for packet header

For the moment I don't have access to an osciloscope to check voltage levels or if the ADUM141E is working properly, so I just wanna check if someone can spot something wrong in my design.

One thing that is probably wrong is that I power the USB part of the ADUM with 5v, and the logic data is 3,3V level. In the datasheet, this figures like is just below the threshold level when 5v is supplied ( VIH = 0,7*5V = 3.5v ).

Thank everyone in advance.

  • \$\begingroup\$ I believe you have it figured out. Logic level converters are not very expensive and do a good job. \$\endgroup\$
    – Gil
    Jul 15, 2021 at 14:25

1 Answer 1


After changing the power supply of the ADUM141e to 3,3V the circuit works flawlessly. And just as a tip, you can use the same 3,3V regulator of the CP2102.

  • \$\begingroup\$ Would using the same power supply not defeat the purpose of galvanic isolation? \$\endgroup\$ Jul 17, 2021 at 10:19
  • \$\begingroup\$ No because I power the USB part of the ADUM with the regulator of the CP2102 and that's all in the usb part of the circuit. In other words, and looking in the pictures that I uploaded, I changed the UVBUS supply of the ADUM for VDD. For the microcontroler part of the ADUM you can see that I use an external 3,3V voltage, that comes regulated from a battery that I didn't show but that the full circuit has. Hope this helps to understand. \$\endgroup\$ Jul 18, 2021 at 14:16

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