I am a new developer and started to work on the ADC part of LPC1549 recently. I am using the development board LPCExpress1549 V2 for learning. I found from the schematic of the board that the VREFN pin (pin14 of 1549) is permanently connected to ground. In effect the range of the ADC is limited to 0v to +3.3V. Why there is no provision for the VREFN to be connected externally (using a jumper etc.) so that the full range of the ADC input voltage can be realized?
Is there any way to connect VREFN to external negative supply?