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When hotplugging a connector on my PCB, my microcontroller gets hot and a short circuit is formed between Vss and Vdd. One pin of the connector is the power supply ground, another is connected to an IO pin, but is driven at ground potential. When this IO pin makes contact before power supply ground, a high current flows trough internal clamping diode D1, destroying it. Is it possible that this shorts the other clamping diode D2, causing a short between Vdd and Vss?

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I have already found a way to prevent this from happening, but I am interested to find out how the short circuit is formed.

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    \$\begingroup\$ Now you know why the v+ and v- pins are longer than the other pins on a typical USB connector. At least I think that's why. \$\endgroup\$ – Harry Svensson Jun 18 '18 at 12:06
  • \$\begingroup\$ I use an RJ45 connector, which is only suitable for hotplugging when it's used for its intended purpose. This problem also occurs with an improper crimp of the rj45 connector where one pin is pressed further down than the others. The PCB is not intended to be hotpluggable, but during development this has happened several times, destroying the microcontroller. \$\endgroup\$ – kva Jun 18 '18 at 13:38
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By connecting an IO pin before connecting ground you caused an unknown (but clearly destructive) voltage to appear between the IO pin and the microcontroller's own ground voltage. If you intend to hot plug the microcontroller you need to protect the connections, preferably by connecting ground and power before the IO signals and also adding components to limit the voltage on the IO lines.

You have catastrophically damaged the microcontroller, so a short from Vdd to Vss would not be surprising. It could happen in several ways. Without knowing the exact structure of the microcontroller's input protection circuitry you would only be guessing at what happened. If you really want to know you will have to pay a failure analysis lab to investigate.

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  • \$\begingroup\$ I intend to add a series resistor to limit the current trough the IO pin to 0.5 mA. \$\endgroup\$ – kva Jun 18 '18 at 14:44

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