MP5991 Css selection & softstart fail

DC-DC Power Converters
1

Hi,

I‘m testing MP5991，here is SCH，Vin is 12V，Vout 12V，Cout 4700uf ,Iout 30A.

Css 100nf.In this condition,Vout fail.Flault_type 0.9V,It seems OTP.

But when I change Css to 47nf,Vout will be normal.

I thought it would be softstart fail，but I can’t find any discription in datasheet. Only an Amplifier in SS pin & MOSFET Gate.Could you help to explain it and I want to know how to select Css in my case.

Thanks！

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1、Css=100nf,Vout（CH2） fail，Wareform below:

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2、Css=47nf,Vout（CH2） ok，Wareform below:

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2

The amplifier between SS pin & MOSFET

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3

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