I noticed a relay driving ac contactor coil (inductive load) resetting the FPGA when energizing relay. there is RC snubber circuit across the coil. Problem disappeared when putting snubber circuit across relay contacts 0.1uF capacitor in series with 47 Ohm resistor. Although this solved the problem but it introduced another problem since the relay passes AC voltage, the snubber circuit gives path to ac voltage when relay is not energized driving small loads.
Out of interest I covered the FPGA with grounded foil tape and problem disappeared even without snubber circuit.
Any ideas or suggestions?
Mahmood