LPC15xx ADC readings

[lpcware]

Content originally posted in LPCWare by kbowers on Thu Aug 28 10:52:42 MST 2014
I am having some issues with the accuracy of the ADC readings on the LPC1549 using the Xpresso V2 board.  I am sampling several inputs using burst mode and am seeing relatively accurate readings on ADC1 but not on ADC0 (about 10% high)  The driving circuitry on all the channels are almost identical.

I have run the calibration cycle on both ADC0 and ADC1 and all the setup configurations are identical.

Is it possible that ADC0 is damaged?  Can I select channel 0 to be the temperature on both ADC's and compare the values to confirm they are both working correctly?

I was also wondering what the VDDA/2 input to channel 0 should read.  Should it not just be 2048 or is there a formula to convert the ADC reading to an actual voltage for VDDA/2.

[lpcware]

Content originally posted in LPCWare by kbowers on Thu Aug 28 11:53:07 MST 2014
The signals are just simple resistor dividers with the lower resistor in the 1k-5k range.  I have tried different sampling frequencies from 10kHz up to 100kHz with negligible changes in the readings.  I am not using channel 0 to monitor anything externally.

[lpcware]

Content originally posted in LPCWare by mc on Thu Aug 28 11:17:30 MST 2014
Hi kbowers,
In burst mode the signal source resistance should be low. How are you feeding the signals?
Yes, VDD/2 should read 2048. Please also note that channel 0 is slow channel  compared to other channels.
What is the sampling frequency?