I have encountered a problem with using the UCC28070 IC in a universal range power factor correction application. The symptom is that the IC turns the PFC regulator stage off repeatedly when the AC input voltage is reduced through about 95VAC at full load. It does not due so when the AC voltage is increased through this point. I have concluded that the problem is that the quantized input feed forward correction circuit changes the loop gain at this point which is essentially a distrubance in the loop. The output voltage of the PFC stage then undergoes a transient response which momentarily increases it's output voltage to the point that the OVP circuit in the IC turns off the PFC regulator. It turns on again approx 10ms later when the PFC output capacitors has discharged sufficiently. This cycle may then repeat meaning the power supply takes energy only from one polarity of the AC line voltage and makes a alarming noise.
Unfortunately the UCC28070 OVP setting is as low as 104% of the regulated output and thus it doesn't take much of a transient deviation to trip it. Also the voltage loop response is necesssarily very slow. I have tried to optimize the voltage loop compensation with very limited success. The only solution I have been able to find to date is to increase the PFC output capacitance significantly which is not a good solution for compact or cost sensitive applications.
Please advise on a better solution.