Jian,
You can find the LM5160DNTBK-CALC calculator here.
For type-3 ripple network stability we have suggested 20mV ripple amplitude, which usually works for most low-voltage outputs.
I think your 24V output has larger output ripple, that dominates type…
Hi Sheldon,
LM5160 is suggested for your application.
Controller solution is not suggested as the load current below 1.5A.
Pls download below calculator for LM5160 Buck conversion
http://www.ti.com/tool/LM5160DNTBK-CALC
B R
Andy