UCC28070: Issue for choke coil current unstable

One customer is considering UCC28070 and UCC28950.

It is based on UCC28070EVM (300W), custom to 2.3kW specification.

(External components are attached below.)

Problem is unstable switching current on choke coil, please let me know about idea for correction points.

Condition and waveform is below;

【Condition】

・Vin: 200Vac (180V~264V)

・External components;

・At first startup UCC28070 on no load.

　When increase output current, choke current become unstable on the moment of discontinuous⇒continuous current.

①Iout: 0.6A (Discontinuous choke current)

　⇒Although a little waveform disturbances, no problem.

②Iout: 0.7A (Continuous choke current)

　⇒Waveform is disturbances and stable on these condition.

　　　I guess that it should sdjust Ton time.

③Startup timing (Iout: 0A)

　⇒The same waveform as ②.

　　　Startup sequence is;

　　　 200Vac (with 20Ω rush current limiting resistor) → When UCC28070 Vcc startup, limiting resistor is short by DC relay on the same timing.

Best regards,

Satoshi