I'm using the LPC11U68, and am seeing rather bad ADC performance. If I run a precision ramp into the input to collect the transfer function, I see that it plateaus at 8 counts before every 64 count boundary, and then jumps up to the boundary. So for example, the ramp will be clean and one to one from 0 to 56, and then the ADC continues to return 56 for 8 steps, and then jumps to 64. Same thing happens at 120 through 128, 184 through 192, etc.
This has been the case with multiple samples of the chip.
Has anyone encountered this? Any ideas? I am running the chip at 3.3V, Ref at 2.5V, and doing the ADC calibration operation per the user manual.