Custom PCB with MDBT40

RE: Custom PCB with MDBT40

ketiljo — Fri, 20 May 2022 08:19:41 GMT

Ok, shouldn't cause any issues like this.

RE: Custom PCB with MDBT40

user116164 — Fri, 20 May 2022 08:04:30 GMT

L1 is a ferrite bead (100Ohm @ 100MHz)

RE: Custom PCB with MDBT40

ketiljo — Fri, 20 May 2022 08:01:19 GMT

Is L1 a ferrite bead or an inductor?

ESD shouldn't be the problem here.

RE: Custom PCB with MDBT40

user116164 — Fri, 20 May 2022 07:44:05 GMT

Hmm yes that would make sense. I will try your recommendation and then maybe implement some ESD protection.

Thank you very much for your help!

RE: Custom PCB with MDBT40

ketiljo — Thu, 19 May 2022 07:03:50 GMT

Sorry for the late reply.

Very strange! Can you measure the voltage on the 3.3 V regulator with an oscilloscope to see if there's any overshoot when you turn on the power? Cal you also replace the regulator with a power supply with current limiting capabilities, set to ~50 mA and see if the same thing happens? The module is probably broken because of overvoltage on some pin

RE: Custom PCB with MDBT40

user116164 — Mon, 16 May 2022 17:51:28 GMT

Thank you very much for your answer. So I checked the voltage before mounting the module. My VDD pins are 3.3V as well as the UART TX pin. All the other pins are low. Is that correct?

I just mounted a new one and only soldered the two VDD and five ground pins. Befor connecting it to the power supply, I checked with a multimeter for a short. Non was found. As I connected the power supply the same happend as with the last ones: it got hot and "died". Afterwards I checked again for shorts and there was one between VDD and GND. After I removed the module kind of forcefully I could also see that there was no shortage between the pins on the backside of the module.

RE: Custom PCB with MDBT40

ketiljo — Mon, 16 May 2022 14:12:21 GMT

There's nothing wrong with the schematic or layout as far as I can see. Check of you have the correct voltage on the correct pins before you mount the module. The module shouldn't need more than VDD on two pins plus ground to operate. Check for solder issues as well.