01-04-2019 02:58 PM
Is there an example of how one can measure a negative voltage rail using the Xilinx System Monitor (XADC)? I see on pg 80 of UG480 that negative input voltages clip to zero code. I just want to measure my negative voltage rails on the XADC if possible.
01-04-2019 05:01 PM - edited 03-06-2019 02:07 PM
EDIT 06Mar19: THIS ANSWER IS WRONG!!! SEE POST BELOW BY @ratter FOR THE CORRECT ANSWER
As shown on about page 27 of UG480, the analog external input channels of the XADC can be configured as bipolar. Then, the XADC can measure negative voltages down to -500mV (see Figure 2-3).
If you have a negative voltage(rail) below -500mV, simply pass it through a two-resistor voltage divider that creates a voltage in the 0 to -500mV range - and feed this scaled-down in-range negative voltage to the XADC.
03-06-2019 09:55 AM
You cannot meaure voltages that are below the analog ground of the XADC (GNDADC). All input voltages must be positive with respect to analog ground (GNDADC). Refer to the Bipolar Input Signals description of page 31 of UG480.
The +/-0.5V range comes from maximum input range of Vp - Vn. Neither Vp nor Vn can be below GNDADC.
Refer to Figure's 2-7 and 2-8 of UG480.
03-06-2019 02:03 PM
Thank you very much for the correction!
Can you tell us what is Absolute Maximum (no damage) analog input voltage for the XADC? I am unable to find this in datasheets for 7-Series devices.
I apologize to many for my error.