I built a scheme similar to the scheme PMP6776(Xilinx Kintex FPGA Power Solution).
I used part of this scheme - a chain of 3 chips TPS54425PWP (2V output), TPS56121DQP(2.5V output), TPS56121DQP(3.3V output). Schemes coincide. The signal PowerGood from TPS54425PWP starts both TPS56121DQP chips. The chips is loaded on several other circuits with high impedance at the inputs(no short circuits). TPS54425PWP starts normally and produces a PowerGood signal. But both TPS56121DQP chips does not starts. Input - 12V, Output - 0.5-0.6V and the signal at the EN/SS pin has the following form: