Difference between LPC1752 Rev2 and Rev3?

[Treczoks]

We ran into some problems with the LPC1752. We designed the board with an LPC1752 marked "ZSD xxxxA" (Rev. 2), and they worked like a charm. But recently, we only got chips marked "SSDxxxxC" (Rev. 3), and even with the same board and firmware, we get crashes. We can reproduce those crashes when heating the processor - it starts at about 40°C. Replacing the "C" chip with an "A" chip and flashing the exactly same firmware with exactly the same setting, and it works like a charm, even if above the chips' temperature limit.

So: What is the actual difference between the "A" and the "C" type?

[Treczoks]

Additional information: It seems to be related to clocking, so I'll explain my clocking setup (that has not changed since it was initially designed ages ago and was worked for years):

External Clock is 12.288MHz, N is 1, M is 32/2, resulting in a PLL frequency of 393.216MHz, which is in the valid range of 275..550MHz. CPU clock divider is 4, so the CPU clock is 98.308MHz. Everything is in spec, and it worked for ages.

With the newer chips, reducing the input clock down to 6.144MHz makes them work - except that everything works slower (as expected), and the PLL is below spec.