lm5118 soft start

Hello Abhishek,

Looking at the LM5118 datasheet information about the SS function, it appears that the IC designers did not anticipate an application with such a long soft-start requirement. It doesn't appear to me that the 10-uF value can cause any harm, but there is another function associated with the SS to help recover from brief but heavy load transients.

In such a case, if the FB signal fell, an internal amplifier will drive the SS cap voltage to track above FB voltage by +150mV so that when the transient abates, the SS should allow Vout to recover softly.
However, the large capacitance may strain the capability of that amplifier to discharge it fast enough to keep on track with the FB voltage and may impair the recovery with a less-than-soft restart. And there may be an outside chance that the amplifier may become unstable at this high capacitive loading under certain conditions.

I'll forward this issue to the appropriate engineer who can address these concerns better than I can, and who may have alternative ideas on extending the SS time.

Regards,
Ulrich

Hi

There will be no stability issue with 10uF Css. SS discharging (by SS-FB clamp circuit) will take a long time due to the huge Css.

Regards
EL