I was testing a 2-channels RS232 adapter for my FPGA board, when I saw this "miracle":
![](https://i.postimg.cc/X7b0CW1f/index.jpg)
If any signal from the RS232 is at a positive voltage and the board is not powered, there is a leakage current to VCC that turns on the led (power indicator).
More, if a VCC = 3.3V is applied the board doesn't work for speed greater than about 300 bps.
Applying a VCC = 5V the board works as expected.
I've used a couple of SP3232E (marked SIPEX that should work @ 3.3V and 5V according to the spec, ah ah...) that I bought from Aliexpress more that one year ago and not used until now:
![](https://i.postimg.cc/26ZP1949/index.jpg)
I really thought that they were fake RS232 IC... so I removed both the ICs and cleaned the pads...
![](https://i.postimg.cc/8ckB2jPd/index.jpg)
Than I've ordered a new lot of SP3232E from TME (
www.tme.eu), and resoldered them
![](https://i.postimg.cc/2jJ1R16z/index.jpg)
...and now the board works at 3.3V and 5V @ 115200 baud and without any "strange" current leakage when not powered...
![Grin](http://www.sonsivri.to/forum/Smileys/SoLoSMiLeYS1/grin.gif)
Here the good SP3232E from TME (in the bottom) compared with the fake one from Aliexpress (upper in the photo and not soldered):
![](https://i.postimg.cc/59vXJxFL/index.jpg)
They look very similar but some differences are anyway visible...
Analyzing the behavior of the fake one, I thing that they are fake MAX232. They seem working at 5V, but the leakage current from the RS232 when not powered suggests not to use them at all...
![Cry](http://www.sonsivri.to/forum/Smileys/SoLoSMiLeYS1/cry.gif)