Hi,
A PCB I'm working on somehow went terribly wrong. As soon as I power up the board, MCU(MSP430F6720IPN) will quickly overheat and in one case literally smoked. So far it happened 4 times, so it is unlikely due to soldering defects. The remaining possibilities should be design or PCB manufacturing related. On a high level, how could MCU overheat or smoke itself? I can think of supply voltage higher maximum rating which is 3.6V, a short to ground on some pin. What else can lead this short/smoking to happen?
The funny thing is, previous revisions of this PCB had been working just fine. In the latest revision, I changed power supply from to AC adapter (5V)+ Lithium Ion battery from AC adapter (5V) + Alkaline battery, and I didn't change any connection to MCU.
So far my observations are:
1) If I remove MCU from the PCB, readings on VCC rail is correct at 3.3V. Also the switch between AC adapter and battery works as expected.
2) MCU overheats even I power the board with a alkaline battery though at a slower pace.
I am kind of out of ideas. If anyone could point me to some direction I would greatly appreciate.
Below is the power supply circuit. It consists of a LDO(XC6227), Lithium Ion charging IC(IC1, MCP72844), On/Off push button IC(IC6, MAX16054). V_ADA{TER and BATT_P are connected to MCU for sensing the presence of AC adapter and voltage of battery. Because I only changed the power supply part from a previous working revision, I think problem should be in this part.
In case of a lithium ion battery is connected, BATT_P will exceed the maximum rating. I thought this could be the problem, but MCU still overheats even I cut the BATT_P trace on PCB. So this could be ruled out.
Many thanks.
