UCC25800-Q1: 励磁电感公式Lm = td/8CSWfSW是如何推导出来的？

Here are steps to derive the formula.

At the end of half cycle, Ipk = Vin/2/Lm * T/2;

Then, the constant current  (Ipk) fully discharge/charge 2* Csw (in parallel) during td.

2Csw * Vin/td = Ipk

Simplified:

Lm = td/(8*Fsw*Csw).