[MOVED] VCC GND SHORT on MCU

[tiwari.sachin]

We have designed a part and most of the times the device is sent back and we find that Vcc and GND are short.

Replacing the MCU solves the issue.

I am unable to understand why this is happening.

I understand that this is a very vague question

The power is right, the system charges up properly... It has required protection, regulation etc... well thats what i believe.

What could be the possible reasons for this?? Any guesses where and what section to check

 

[moh.haroun]

Re: VCC GND SHORT on MCU

VCC and GND of the device are shorted implies that the device is burnt out. This might be due to the power network you have or simply a bad product from origin.

 

[FvM]

Re: VCC GND SHORT on MCU

Of course, we can't say much without seeing a detail schematic. As an initial guess, I would consider

- massive Vcc overvoltage events, e.g. > 7V for a 5V device
- latch-up triggered by input voltages at any pin beyond the supply rails. Due to lack of current limiting means, the rated clamp current is exceeded.

 

[KlausST]

Re: VCC GND SHORT on MCU

Hi,

.. or overheating of the device...
(Overvoltage on supply or signals is more likely)

Klaus

 

[tiwari.sachin]

Re: VCC GND SHORT on MCU




This is the power sequence that I am using... Input can vary from 7 to 9.5V.

VDM is also used by some peripherals.

5V by USB Host

3.3V for MCU, memory, bluetooth etc


Just found that in one of the board, a bluetooth module is damaged, we replaced it and it worked fine.


I tried to remove the 1R resistor too but I donot have access to tools that can measure rapid changes etc.

Removing 1R also, it works fine... but when will it break down... well thats kind of puzzle

 

[moh.haroun]

Re: VCC GND SHORT on MCU

If you have a high speed component that would be a possible reason. If so you should provide an independent regulator for those high speed components that can handle its requirements.

 

[KlausST]

Re: VCC GND SHORT on MCU

Hi,

1) bluetooth module: what supply voltage?
2) show us the PCB layout.

Klaus