3.3V line shorted to 5V

Thread Starter

andrew74

Joined Jul 25, 2022
55
Hi! I recently bought a transceiver (two same pieces) to use with the STM32F407 for serial communication with UART. Unfortunately, I don't remember its name (whose photo I enclose).

It has always worked, but today by connecting it to the computer I noticed that it got very hot and smelled burnt. Luckily I have two of them so I tested the other one and noticed that it worked, didn't get hot and everything was fine.

I think the problem was the jumper between 3.3V and 5V that I forgot to connect... it might have short-circuited the power supply... am I wrong?

20220903_141159.jpg20220903_141152.jpg

Actually, I don't know if it's broken because I haven't tested the programme (I send a string from STM32CubeIDE to Tera Term), being afraid to leave it attached to the computer as it heats up quickly. But anyway the overheating is abnormal.
I still tried to connect it by disconnecting the jumper, but it still overheats so I think the damage is irreparable.

I only ask for confirmation that the main cause could have been that short circuit.

Thanks .. and sorry for the stupid question!:D

I also take this opportunity to ask if there should be protection to avoid this inconvenience :/
 

MrChips

Joined Oct 2, 2009
27,186
I think the problem was the jumper between 3.3V and 5V that I forgot to connect... it might have short-circuited the power supply... am I wrong?

I only ask for confirmation that the main cause could have been that short circuit.
I would have to assume that what you wrote is a typo error.
You meant to say "I think the problem was the jumper between 3.3V and 5V that I forgot to disconnect" .

Never join 3.3V and 5V pins with a jumper. Both of these pins are outputs.
5V pin is the USB power output.
3.3V pin is output from the FT232 chip.

Connecting the two pins will damage the FT232 chip.

The circuit is called an FT232 USB to TTL converter. There are many versions of this converter being sold.
 

Jon Chandler

Joined Jun 12, 2008
391
Actually
this board
uses a CH340 USB-UART converter chip, not an "FT232" as MrChips stated.

It looks like the module is supplied with a jumper on the 5 pin header. This jumper is meant to connect Rx and Tx for a "loop-back" test – whatever is typed on the computer is echoed back to the computer. It's not really useful other than for connecting Rx and Tx together for testing.

It would not be used when the module is connected to the micro board. Best to throw it in your junk box. It probably got connected between the 3.3 & 5 volt pins for "safe keeping" the last time you used the module. That has probably destroyed the 3.3v regulator on the board.

SmartSelect_20220903_084736_AliExpress.jpg

SmartSelect_20220903_084534_Edge.jpg
 

Thread Starter

andrew74

Joined Jul 25, 2022
55
I would have to assume that what you wrote is a typo error.
You meant to say "I think the problem was the jumper between 3.3V and 5V that I forgot to disconnect" .

Never join 3.3V and 5V pins with a jumper. Both of these pins are outputs.
5V pin is the USB power output.
3.3V pin is output from the FT232 chip.

Connecting the two pins will damage the FT232 chip.

The circuit is called an FT232 USB to TTL converter. There are many versions of this converter being sold.
You are right! I meant to write 'disconnect'.
Thanks
 
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