I have designed a PFC module using the UCC28063A aiming for 600W. The module works ok without load but with even a load of 2.5kOhm the output voltage drops to 286V. At the beginning of each AC line cycle the two phases have about 180 degrees difference but around the middle of the cycle they become in phase... and also the ZCDA and ZCDB become in the range -5V~+5V.
Any suggestions? Are the inductors saturating?