EDIT 3 The correct solution is shown below, in TurboJ's answer in fact, this exact issue was mentioned in the LPC4300 errata ES_LPC43x0:
EDIT: Nope, sorry false alarm. The new board started doing the same thing:(
EDIT 2: I'm beginning to wonder if poor layout is to blame. The +3V3 rail is shown. Because the board is a 2 layer, I had to forego the traditional power plane and power is provided by a single 6 mil trace. I noticed that the problem never occurred on a board with no decoupling capacitors populated, but started to happen when I added the .1uF capacitors.
I have a board with a LPC NXP 4330 (ARM Cortex M4/M0 dual core) microcontroller, in a TBGA-100 form factor. The power situation is complicated because I have sensors which require precision 4V power, so the main supply needs to be a LDO drop above 4V, so it is powered in the following way:
3.7V Lipoly or USB (controlled through MAX1555 battery charger) -> 4.5V step up/down switcher (TPS63061 integrated switcher) -> 3.3V low-drop out linear (LP38691) -> LPC 4330
I have noticed that on startup, the micro will start up very hot (too hot to touch) for a second, before settling down to a more reasonable temperature. When it does this, I can communicate through the JTAG just fine and run my application. It will always start up like this when connected to a 4.5V bench power supply (bypassing the switching regulator completely). The surge current is very high, up to a couple hundred of mA, as the spike in temps confirms.
When connected to the switcher (fortunately it is on another board, so it is easy to bypass), sometimes it does not start up. I assume that this is because the surge current is causing the switcher to shutdown because it goes into some over-current mode. If I disconnect the switcher from the load, plug in the battery first, and then plug it back into the load, it will cause the micro to get hot (as usual) and then work.
Is this normal behavior for the LPC 4330? It seems fairly unusual that a microcontroller would take several hundred mA to startup (where is all that current going?) Is there a way to prevent this initial current inrush when the entire circuit is hooked up.
I've included a schematic, I will need to run tests on the supply ramp up on Monday.
Main micro-controller board
Power and USB connector board
Layout showing +3V3 rail