• State Resolved
  • Locked Locked
  • Replies 5 replies
  • Subscribers 63 subscribers
  • Views 789 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TPS54061 EMI concerns

Natallia Holubeva1
Expert 6550 points
Other Parts Discussed in Thread: TPS54061, TPS54062

Hello e2e,

My customer is using this controller in an application with pretty low current draw, possibly down to around 15mA.  The datasheet seems to recommend to use DCM for that, but he is concerned about EMI so intend to use it in CCM.  Any concerns with that?

Thank you very much!

  • 0
    TI__Mastermind 35115 points

    Hi Natallia,

    The DCM design procedure is recommended for lower noise because the equations select an inductor that will keep the IC from pulse skipping at the minimum load. When pulse skipping some of the noise from the TPS54061 will be at a lower frequency as the IC is in a way switching at a lower frequency.

    If they prefere a CCM design when selecting the inductor I recommend them a KIND value very close to 1 due to the low current. Is there any reason they are not using the TPS54062 instead?

    Best Regards,
    Anthony

  • 0 in reply to Anthony F
    TI__Expert 6550 points

    Hi Anthony,

    Is there any benefit in changing to the TPS54062 at this point?  The datasheet gives the same disclaimer about going to DCM for low currents as does the other.  Looks identical just has lower output current maximum.  If we stayed with the 61, we have some margin if for some reason we need additional current, and could always swap out with the 62 later if we don’t need additional current.My concern about DCM is potential emissions concerns during EMC testing..these boards will not be inside the shielded/enclosed system so there is risk of emissions there.

    Best Regards,

    Natallia

  • 0 in reply to Natallia Holubeva1
    TI__Guru**** 191445 points

    I hate to jump in here, but for CCM operation you need a lower value of KIND I think.  If the inductor current reaches zero then pulse skipping occurs.  So to prevent that, low KIND means higher L and lower ripple current = CCM.

  • 0 in reply to JohnTucker
    TI__Mastermind 35115 points

    John is right that typically you need a lower value of KIND to stay in CCM longer. However in this case with such a light maximum load, I recommend a KIND closer to 1 to keep current ripple larger to get the best performance out of the TPS54061. The IC was designed for 200mA load where the current ripple is usually around 50 mA minimum. The current ripple is important because it's used for the PWM control. If the current ripple becomes smaller it may become sensitive to noise causing jitter in the switching waveform. The TPS54062 was designed for smaller currents and will work better with smaller amounts of current ripple.

    They could try using the TPS54061 with a small current ripple but this is something to watch out for in the future. If they run into some strange performance issues related to jitter or an irregular switching waveform they could reduce the switching frequency or inductance to see if it helps.

    Has this customer had emissions issues with DCM on other projects in the past?

  • 0 in reply to Anthony F
    TI__Expert 6550 points

    Anthony,

    Thank you very much for such a good job explaining! To answer your question, there is up to 48 of these circuits on the outside of our shielded area of the design, so want it to be least noise as possible.

    Natallia