TPS54160: Ring occurs before conduction at PH node in PSK mode

Hi team,

I meet a problem while TPS54160 in pulse skip mode.

As you can see, there are rings before conductionat PH node.  Top to bottom signals are Vout, PH, IL, PG.   

Vin= 25V,   Iin=4.55mA,  Vout=3.336V, Iout=24.7mA, fs=250kHz

But in CCM mode, the signal is normal.

The schematic is as follows,

Thanks for your help.