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LM5122: fluctuating dutycycle of LM5122

Zhuoxun Liu
Prodigy 60 points
Part Number: LM5122

Tool/software:

Hi expert,

The blue wave is inductor current IL and the purple wave is SW, as you can see the dutycycle is fluctuating. Could you please share with me the reason for fluctuating dutycycle?

The testing board is PMLK Boost EVM 

Vin=15V, Iin=0.696A, Vout=24.127V, Iout=0.4A.

  • +1
    TI__Mastermind 29640 points

    Hi Zhuoxun,

    Thanks for using the e2e forum.

    The waveform seen shows indeed some oscillation which could be related to slope compensation or loop compensation instability.
    The PMLK Boost EVM has several ways of modifying inductance, switching frequency, loop and slope compensation values.
    If the combination of these settings is chosen non-ideal, it may lead to the instability you are seeing on the scope.

    A quick check would be to change the jumpers for slope compensation (J14) and loop compensation (J18-20) and see if the behavior becomes stable.

    Best regards,
    Niklas