UCC28251: Switching frequency problem

Part Number: UCC28251

Hello!

I have a problem with switching frequency after power-on. In my circuit Rt = 75KOhm (Fsw = 100KHz), Csoftstart = 100nF.

When I "power-on -> power-off -> power-on immediately" -> Fsw = 50kHz.

When I "power-on -> power-off -> wait  for 15s -> power-on" -> Fsw = 100kHz.

When I "power-on -> power-off -> discharge Csoftstart  immediately -> power-on immediately" ->  Fsw = 100kHz.

What happens with Fsw after fast power cycling?

Thanks.

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