The PCB I am working on somehow went terribly wrong. As soon as I power up the circuit, MCU(MSP430F6720) starts to quickly overheat and in one case literally smoked. I described this in TI's forum here, but in a general sense, what leads this overheat/short of MCU to happen and how can I troubleshoot the issue?
My understanding is: somehow, either by design or manufacturing of PCB, a short circuit was created inside MCU: 1) Some pin is illegally connected to power supply rail (VCC); 2) Some pin is illegally connected to ground; 3) Power supply voltage exceeds the maximum rating of MCU. Did I miss something here?
Funny thing is, the PCB had been working just fine till I changed the power supply circuit from AC adapter + alkaline battery to AC adapter + lithium ion battery. So now I am kind of back to square one. Any input would be greatly appreciated.
Edit: below is the power supply circuit I used in the problematic PCB. Because I only changed this part of circuit from previous revision, I believe the problem is in this part. The circuit consists of the following three parts:
1) LDO: xc6227, this IC is also used in previous revisions. 2) Lithium Ion charging IC: MCP73844. This circuit has been used in my other PCBs. 3) On/Off push button IC: MAX16054. This is used to turn on/off the power supply.
Update: the problem turned out to be feeding voltage of lithium battery into the analog input. The new PCB with this problem fixed works just fine. Thanks goes to everyone.