I'd like to replace the battery attached to VCC_PSBATT in Zync UltraScale+ RFSoc device with a super capacitor. Where can I find guidelines how to connect it ? Does it need to be connected to VCCAUX through a resistor ? what it the resistor value ?
Most likely the super/ultracapacitor vendors or distributors. I believe Xilinx itself has been testing and qualified with the standard battery as back up power source so we do not have specs or guidance on that yet. I don't see why this would not work if you ensure the supply specs are met at the Zynq RFSOC device. Caps do discharge so they will have a different supply profile and that needs to be considered. You will need to charge it from a power source in certain intervals to keep the voltage within the supported 1.2-1.5V range.