LP38851 / Loop stability

S.Satoshi

Other Parts Discussed in Thread: LP38851, LP38852

Hi Team,

I would like you to share the example data of loop stability of LP38851. Now our customer is evaluating LP38851 and measure LP38851 as attached but they could confirm low gain margin. Now I prepare to measure it in our lab but it will be appreciated if you provide example data.

Our customer is using LP38852EVM and replace the device from LP38852 to LP38851 because LP38851EVM is not available.

Best Regards,

Sonoki / Japan Disty

LP38851 control loop measurement.pdf

over 10 years ago

0 S.Satoshi over 10 years ago

Guru 21675 points

Hi Team,

I tried to measure loop stability of LP38851 which is mounted on LP38852EVM. The result was similar with our customer as attached. So I'd like to know if this result is suitable performance. Please give your comment or show your example data.

Best Regards,

Sonoki

LP38851 control loop measurement_our result.pdf

0 S.Satoshi over 10 years ago in reply to S.Satoshi

Guru 21675 points

Hi Team,

I measured the loop stability of LP38852 also. I used the recommended Cff in LP38852's datasheet then I confirmed good result. Now I found that LP38851 recommend the Fz around 600kHz, and LP38852 recommend around 10kHz. I'm concerning that the 600kHz of Fz may be too high, so we can not see the effect of Cff.

Your comment will be appreciated.

Best Regards,

Sonoki

0 S.Satoshi over 10 years ago in reply to S.Satoshi

Guru 21675 points

The measurement result is attached.

Sonoki

LP38851, LP38852 control loop measurement.pdf

0 Donald Jones over 10 years ago in reply to S.Satoshi

TI__Mastermind 22610 points

"... So I'd like to know if this result is suitable performance ..."

In general, if there is minimal output voltage ringing during load steps, then performance is suitable for typical users.

Customer opinion will define if this is suitable performance for thier application. They are certainly free to change the Cff value to a larger (or smaller) value if they believe that there is some need within their specific application.

As to the unasked question: "why are the tables different?", I don't know, the tables should be the same.

0 S.Satoshi over 10 years ago in reply to Donald Jones

Guru 21675 points

Hi Donald-san,

Thank you for your response. I'll suggest our customer to change the Cff value if they need to adjust Fz value in their system.

Best Regards,

Sonoki

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LP38851 / Loop stability