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LM5117: problems simulating

Part Number: LM5117

Hi TI Team.

I am trying to simulate a design using the lm5117 but I encounter different behavior on different simulation software with a lot of problems on both softwares

I tried simulating the design on TINA TI and on PSPICE FOR TI.

PSPICE FOR TI:

No mater what I do I cant get the output to go above 45mV when my feedback is designed for 24V output.

Tina TI:

using the exact same design I am able to get the output that I want, but the moment that I try to add another input capacitor (even small one..1pF) the output goes to zero..

I cant understand why the design works on one software and on another it doesn't... also, why adding the small cap in the input changes the output so drastically ?

 

IMPORTENT NOTE: 

THIS DESIGN IS ALREADY IMPLANTED ON A PCB AND WOKING! ( I Just need to improve little thing on it)