Power management

Power management forum

LM5008: Excessive ripple

Jeff Starkell

Intellectual 490 points

Part Number: LM5008

Just powered up a new circuit using a LM5008 and the ripple voltage is excessive. Varied the load from 10-40mA, with little effect on the ripple.

Circuit and waveform attached, incorrect component? How best to troubleshoot?

over 7 years ago

0 David Baba over 7 years ago

TI__Mastermind 35180 points

Hello Jeff,

Please can you provide me with you specification?
Vin min/Max
Vout/Iout

Any other important requirements needed to take in to consideration for your design?

Thanks.

David.

0 Jeff Starkell over 7 years ago in reply to David Baba

Intellectual 490 points

David,

Vin 22 to 40Vdc

Vout for circuit shown was about 3.9V, however I just adjusted it up a bit to 5.25V (for another reason)

I out ranges from about 8mA to 20mA

0 David Baba over 7 years ago in reply to Jeff Starkell

TI__Mastermind 35180 points

webench_design_463344_708_446577639.pdf

Hello Jeff,

Recommend following the following design to meet your requirements.

See attached.

Hope this helps?

David.

0 David Baba over 7 years ago in reply to Jeff Starkell

TI__Mastermind 35180 points

Hello Jeff,

Sorry, i just checked your layout.

I would move the feedback resistors and feedforward cap close to the IC.

Hope this helps.

David.

0 Jeff Starkell over 7 years ago in reply to David Baba

Intellectual 490 points

David,

Thanks for that, R17 (Ron) was the problem, 20x improvement. I'm going to move the FB resistors close to pin 5 for good measure

0 Jeff Starkell over 7 years ago in reply to Jeff Starkell

Intellectual 490 points

Tweaked layout attached, better???

0 David Baba over 7 years ago in reply to Jeff Starkell

TI__Mastermind 35180 points

Yes, much better.

0 Jeff Starkell over 7 years ago in reply to David Baba

Intellectual 490 points

David,

Thanks for your help, effective and timely advice is priceless, have a great day.