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LMR23625CFPEVM: Spike noise

Taketo Sato
Genius 9955 points
Part Number: LMR23625CFPEVM
Other Parts Discussed in Thread: LMR23625

Hello team,

My customer has observed spike noise as following with LMR23625CFPEVM and I would like to know the cause of the noise.

No load: 40mVpp spike noise

1A load: 80mVpp spike noise

Also, the spike noise becomes bigger when placing one EVM very close to another EVM for those inductors to be very close. two EVMs are in SYNC operation.

They observed also spike noise level gets small when changed an inductor to be big size from small size, which means distance between LMR23625 and inductor becomes shorter.

Can I think the spike noise customer observed is due to EVM layout, especially distance between device and inductor?

or please suggest if there is any other reason?

Best regards,

  • 0
    TI__Expert 3835 points

    Hi Sato-san,

    Increasing the load current will causes high current ripple in the inductor which will increase the output voltage ripple. Putting the EVM and conductors close together means that the noise is coupling to each other and amplifying the noise that are synced together. 

    Layout can be factor since the EVM is designed to fit multiple inductors. Putting inductor closer to the SW will minimize the loop path and can minimize noise.

    Increasing the inductor value can reduce current ripple. I would suggest calculating where the current ripple factor is less than 30%.

    Regards,

    Ethan

  • 0 in reply to Ethan T
    TI__Genius 9955 points

    Hello Ethan-san,

    That sounds like the spike noise on Vout customer observed is due to layout.

    Is it possible for you to estimate how much level of spike noise can be seen when optimizing inductor placement?

    Best regards,

  • 0 in reply to Taketo Sato
    TI__Expert 3835 points

    Hi Sato-san,

    Unfortunately, you want to optimize inductor placement where output voltage ripple does not become a factor in the equation. The equation below factors in the inductor ripple current, switching frequency, ripple factor, load current, and output capacitors. The noise from layout would be considered a parasitic which can't be estimated.

    Regards,

    Ethan