Why is VREFN (pin 14) is permanently connected to GND in LPC1549 LPCExpresso V2 board? It limits the full range of the ADC to half - from GND to VREFP only.

[vijaynaik]

Hi,
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?

[soledad]

Hi,

This board was designed for positive values, however you can modify de board connectios (open) according your needs.
The measurement range VREFN to VREFP is typically 3 V; this range should not to exceed VDDA voltage level.

Have a great day,

Sol

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[vijaynaik]

Hi Sol,
Thanks for the reply.
But how to disconnect the pin (14) of the IC from the ground connection because it is soldered into the track? Is there any removable jumper or solderable pad on the board to give external negative supply to this pin? 
Please clarify.

Vijay