Zedboard power consumption suddenly drops for designs above 4W
I am measuring the power consumption of a few designs on the Zedboard. I am using the sense resistor at J21 to measure the voltage across it so that the current consumption followed by power consumption can be calculated.
For most designs where the power consumption is higher than around 4W, the power consumption suddenly and randomly drops by around 50mW. I cannot figure out the reason for this.
For example, consider the design where the voltage on the sense resistor is 3.66mV => current consumption = 3.66mV/10m-ohm = 366mA. This results in a power consumption of 366mA x 12V = 4392 mW (4.392W). After the design in programmed, in sometime, the voltage suddenly drops to 3.62mV => 4344mW (4.344W), i.e a drop by 48mW.
This happens for most of the designs where power consumption is close to 4W, and is rare (but happens sometimes) for designs with lower power consumption.
Why would the power consumption drop suddenly? The ARM core is also running a code along with the FPGA design. So does soemthing in the ARM shut down? or Does the board have some protection beyond 4 W? Please help me with this issue.