LM5143: LM5143 Output oscillation at independent dual output operation

Roshan Anto Singh R H

Part Number: LM5143

Tool/software:

Hi,

I'm using LM51343 for converter (9V to 12Vin, Vout1- 8.5V at 5A and Vout2 - 5V at 5A). At 12Vin my converter was working fine.

But 10.5Vin my 5V output starts to oscillate at 1Khz to 5Khz. So I suspected it was compensation loop issue.

So I disabled the 8.5V and tested the 5V output. It was working fine and no oscillation at output.

Also I disabled the 5V and tested the 8.5V, No oscillation at output.

But I tested it dual output configuration. The 5V was oscillating.

Also it switch node was oscillating at cycle by cycle.

My inductor value 6.8uH, DCR 6.15m ohm

CS RC value:

5V: 7.5K ohm & 0.2uF

8.5V: 12.7K ohm & 0.1uF

Compensation value

C: 330pF

RC: 20K ohm & 0.01uF

5V switch node

Regards

Roshan

2 months ago

0 Onkar Bhakare 2 months ago

TI__Genius 17936 points

Hello Roshan

Could you please share your full schematic? Additionally, share the complete QuickStart for your design to review the compensation and other power stage components

Thank you

Regards

Onkar Bhakare

0 Roshan Anto Singh R H 1 month ago in reply to Onkar Bhakare

Prodigy 40 points

Hi Onkar

Sorry for late replay

Refer my buck converter SCH and QuickStart design sheet in attachment

Regards,

Roshan

4667.LM5143 SCH.pdf

LM(2)5143-Q1 quickstart design tool - revB2.pdf

0 Onkar Bhakare 1 month ago in reply to Roshan Anto Singh R H

TI__Genius 17936 points

Hello Roshan

Could you please share QuickStart in .xlsm format? I am not able to access it

Thank you

Regards

Onkar Bhakare

0 Roshan Anto Singh R H 1 month ago in reply to Onkar Bhakare

Prodigy 40 points

Hi Onkar

Sorry for late replay

When i uploading the QuickStart in .xlsm format, the file type was not uploaded.

Also i changed my buck converter input voltage from 10.5Vin to 14V. the sub harmonic oscillation was reduced, still the 8.5V & 5V output oscillates at 400Hz refer below image

8.5Vout at 14Vin with 2A load

5Vout at 14Vin with 2A load

8.5V SW at 12Vin with 2A load

Regards,

Roshan

0 Onkar Bhakare 1 month ago in reply to Roshan Anto Singh R H

TI__Genius 17936 points

Hello Roshan

I'll get back to you by EOD

Thank you

Regards

Onkar Bhakare

0 Onkar Bhakare 29 days ago in reply to Onkar Bhakare

TI__Genius 17936 points

Hello Roshan

As DCR sensing being used here, the time constant of RC and L/r should match. With present values, these time constants are not matching. Could you please update the RC and see if it helps

Thank you

Regards

Onkar Bhakare

0 Roshan Anto Singh R H 29 days ago in reply to Onkar Bhakare

Prodigy 40 points

Hi Onkar

I set the inductor DCR time constant & CS RC time constant as same, (Value L: 6.8uH, DCR: 6.1m ohm. CS RC, R: 7.5K, C: 0.2uF). But there is no improvement.

Regards,

Roshan

0 Onkar Bhakare 29 days ago in reply to Roshan Anto Singh R H

TI__Genius 17936 points

Hello Roshan

Could you please share datasheet of the chosen inductor? I would like to review the saturation current rating of it. As per the calculation inductance value appears to be okay. But the problem you are seeing is pretty similar to subharmonic instability. Meanwhile try doubling the switching frequency and see if it helps.

Thank you

Regards

Onkar Bhakare

0 Roshan Anto Singh R H 29 days ago in reply to Onkar Bhakare

Prodigy 40 points

Hi Onkar

Inductor value: 6.8uH (IHLP6767GZER6R8M11)

I increased my buck converter switching frequency to 812Khz but there is no improvement.

Regards,

Roshan

0 Onkar Bhakare 26 days ago in reply to Roshan Anto Singh R H

TI__Genius 17936 points

Hello Roshan

The schematic and component selection appears to be okay. I couldn't find any problem which relates to this issue. Could you please share you layout for review?

I am attaching QuickStart of the design for review.

8831.LM(2)5143-Q1 quickstart design tool - revB2.xlsm

Thank you

Regards

Onkar Bhakare

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LM5143: LM5143 Output oscillation at independent dual output operation