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regulator with mmbt3904 - helpneeded

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hhchien

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regulator with mmbt3904

Dear all:

I've design a regulator with an off chip npn(mmbt3409) as pass element(common emitter),

I put the dominant pole at collector of 3904(CL * Rout),

With the download model on NXP, Spice simulation seems OK.

But when I measure that chip, it rings.

Did you have any experience like mine, measurement can't be predicted by spice simulation??

What should I do to improve my design, please help me, thank you very much.
 

regulator with mmbt3904

I guess, you didn't consider bond wire inductances in simulation.
 

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    hhchien

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Re: regulator with mmbt3904

FvM said:
I guess, you didn't consider bond wire inductances in simulation.
Click to expand...

Thanks for your reply.

What value should I use ?? 10n or 20n??

Thanks a lot
 

regulator with mmbt3904

I would expect below 10 nH, but I don't know your geometry. I once learned, that I have to use package parasitics in simulation to get meaningful results. For standard packages, the values can be taken from manufacturer SPICE libraries.
 

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    hhchien

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regulator with mmbt3904

Dear FvM:

Sorry to bother you again.
I've try the package parasitics , but still can't see the problem on real environment. Could you give me some other suggestion please??

Thank you very much..
 

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