LM5015 output noise

Bob Richards

Other Parts Discussed in Thread: LM5015

Hello I have an issue with extreme noise on the output of the LM5015 when used in Isolated two switch forward mode.

The circuit I am using is that shown in the data sheet (figure 25) with the exception that the output is set for 3.3V (transformer and feedback set accordingly) component values have been chosen using the TI spread sheet calculator. I am seeing spikes of noise (switching noise) up to 2V PP on the output. The noise increases in proportion to the input voltage and/or load (48-60V input 0-4A output). I am on my second layout as the first was compromised. The current layout is near identical to the evaluation board. All capacitors are low ESR ceramics and tantalum. PCB is multi-layer with solid ground planes but no overlaps from ISO areas.

Schematic AttachedC28002-00 - PSU.pdf

Any help would be much appreciated.

Thanks

Bob

over 9 years ago

0 LeonardEllis over 8 years ago

TI__Guru 71526 points

Hi Bob,

I have moved this post to AC/DC Forum where it will get the attention from an LM5015 specialist.

We will analyze the schematic, and most likely will need to see the layout as well. In the meantime, here is a similar E2E post: https://e2e.ti.com/support/power_management/isolated_controllers/f/188/p/236866/831625#831625 .

As well, a couple App Notes on adding a Snubber for noise reduction:

http://www.ti.com/lit/an/snva638a/snva638a.pdf , and http://www.ti.com/lit/an/snva489c/snva489c.pdf and /cfs-file/__key/communityserver-discussions-components-files/196/8117.6523.0652.RC-Snubber.pdf .

~Leonard

0 David Baba over 8 years ago

TI__Mastermind 40040 points

Hello Bob,

When you describe the noise gettingworse, I am assuming with increasing load? Does it get worse with decreasing the input voltage too? Also what type of noise are you seeing? Is it high frequency noise spikes on the output DC voltage? Or is it jitter on the Switch node causing excessive ripple on the Vout?

Thanks in advance for clarifying.

David.

0 Bob Richards over 8 years ago in reply to David Baba

Prodigy 20 points

Hello David

Thank you for your interest.

Its taken a while for this query to reach this bulletin board so things have moved on quite a bit. In truth I believe the noise I have been seeing on the output (set to 3.3V) is mostly due to my poor measuring technique! The transformer is producing an impressive amount of radiated RF which the scope was picking up on its leads. By using better quality leads and closer ground coupling, measured figures are now within acceptable limits.

At this point in time I don't think we have any further issues with this circuit but should they occur I will update.

Kind Regards

Bob

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LM5015 output noise