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LM25011: Soft Start function

Part Number: LM25011

LM25011 is damaged when Css value increase(0.122uF) at input voltage ON/OFF test.

Do you have any cause that LM25011 is damaged by increasing Css value?

Vin=34V, Vout=26V, Fsw=500kHz, no load condition.

And I would like to know Css discharge function. On datasheet block diagram, I think SS pin has FET for discharge.
When does this FET turn ON? Is there possibility that Css is not full discharged because capacitance value is large, and Vin is added in this condition, then LM25011 is damaged?

Best Regards,
Kohei Sasaki

  • Kohei,

    The soft start pin goes to a 10uA current source. Increasing the soft start capacitance would not directly damage the IC but as you mention, the slowed effects of soft start might.

    Your theory is not impossible but you would have to turn VIN off for a very short period of time. SS will discharge during thermal shutdown and UVLO as shown in the block diagram.

    You can prove your theory by testing again while observing the SS and VIN voltages with a scope.

    -Sam