We designed MPC8548E based board. We r using Linear Technologie's 15A power module (LTM4611) to power the core of PowerPC. We are following a powerup sequence of VDD_CORE --> I/O supply (or as specified in datasheet). Initially after board power on, we are not feeding any clock or reset to processor, We are just powering on the core voltage(Note that at this moment no IO is active), at that moment, we are noticing a strange behaviour, powerPC is getting heated up like any thing and it is drawing a current of 10A.
There is no short between VDD_CORE and GND plane (Impedance measured between these rails is 5 Ohms).
Using X-Ray we have seen the assembled PowerPC BGA, there are no traces of ball to ball short.
Then what could be the reason for this unusual behaviour?
I am attaching, the powersupply portion of the schmamtic... Please reply immediately to my query because we can not proceed futher, if this is not working