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LM5176: Current ripple is not stable

Kai Hsiao
Guru 12675 points
Part Number: LM5176

Hi Sir 

When the VIn is close to Vout ,the inductor current is not stable ,please refer below figure 2 and figure 3 

Do you have any idea how to modify this issue ? 

Schematic as below 

SPEC : VIn=10V~30V to Vout=24V / 3.75A

Schematic 1.pdf

Schematic 2.pdf

Vin=20.8V

Vin=21.9V

Vin=22.8V

Vin=25.2V

  • 0
    TI__Guru* 76005 points
    Hi Kai,

    Thank you for using the LM5176. Can you reduce Cslope to 150pF and see if there is any improvement?

    Thanks,
    Youhao Xi
  • 0 in reply to Youhao Xi
    Prodigy 10 points

    Hi Sir,

    I've modified the value of Cslope with 100pF, 150pF, 1000pF, 10nF, 100nF respectively, but the behavior is almost the same.

    I'm curious that the intervals of pure buck and pure boost are definitely stable, only the transition intervals will become unstable,

    Is there any reason for this? or do you have any comment to cope with this unstable issue? Thank you for your highly support 

    and look forward to your quick response.

    Best regards,

    Raymond Yu

  • 0 in reply to Raymond Yu
    TI__Guru* 76005 points
    Hi Raymond,

    It seemed your layout is not clean and you should modify according to the datasheet layout guideline, and also reference to our EVM layout for how to place the power circuits as well as critical control circuits.

    Thanks,
    Youhao