We used an external voltage divider to 10k--1k (0.1%) to feed the monitor of the 12V voltage to LPC1778 ADC. We measured the ADC input voltage was 1.147V after the voltage divider while we expected 1.091V. We so decreased the voltage divider resistor values to 1k--100ohm and got the the 1.0974V measured. My questions are
1. From LPC1778 datasheet, Rvsi is 1kohm max. Our original picked resistor values met this Rvsi, but why still got wrong voltage?
2. We used a 68nF capacitor for the filtering in the ADC pin while the datasheet lists Cia is 5pFmax. Any affect for not complying this requirement?