Nucleo boards get fried as soon as I connect charger to my MacBook Pro

[surumadurum]

After working a while with a brand new Nucleo WL55JC1 (power jumpers untouched) connected to my MacBook Pro (2017), my laptop battery was empty and I connected the charger.

Charging behaviour was strange, laptop switched from "charging" to "not charging" and back every second or so. This would go away when unconnecting the Nucleo.

After some minutes, the nucleo was not detected right away anymore when I wanted to upload new firmware, but it still worked after I re-plugged it.

Some minutes later, also this did not work anymore, the board became completely unresponsive, just some parts became extremely hot when connected to USB.

I thought I wasnt careful enough with ESD protection, input protection or whatever, so I just reordered some cheaper Nucleo R476RG, so I could figure out what the issue was.

Today same thing with the R476RG: After working without problems for about 3 hours, I connected my laptop charger, right away some part on the top right corner of the PCB burnt with smoke (is it the voltage regulator?), after that, completely bricked.

Is this a pcb design flaw?

Is it related to the laptop being charged by USB-C?

Anyone else experienced this?

[Peter BENSCH]

If you talk about "top right" on the NUCLEO-L476RG, whereby this is not defined and "top" probably means the position with the ST-LINK interface on top, then U1 (SOT23-5) has probably been destroyed. That is a voltage regulator (LDO), which can handle max 6V input voltage and is grilled with higher voltage.

This looks like a higher voltage is applied to the 5V line of your computer with a charger connected.

Maybe you can check this by connecting the charger and measuring directly at the USB-A socket, possibly via a USB extension cable?

Regards

/Peter

[surumadurum]

Thanks for your reply Peter!

While checking with a voltmeter didn't show any anomalies, today re-checking with a scope revealed that when laptop is plugged in and i connect sth to a usb port, I sometimes get a spike of around 7V for around 10ns.

 

Crosschecking with a Surface Pro, I did not get spikes when plugging in the usb peripherial probe, but when plugging in the charger, a similar thing happened:

 

So, is this likely to be the thing frying the Nucleos?

The thing is that when plugging in my MBP, there are no spikes on the output, but thats what led to a burnt LDO. Could it be related to USB enumeration?