• State TI Thinks Resolved
  • Locked Locked
  • Replies 3 replies
  • Answers 2 answers
  • Subscribers 63 subscribers
  • Views 190 views
  • Users 0 members are here
Support feedback
Options
Options
Related

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.

LM25117: Issues adding beads to the design

David Huang
Intellectual 2285 points
Part Number: LM25117

Hi team,

My customer reported the device got into OCP after adding Mn-Zn beads, while no issue reported with Ni-Zn beads.

Could you please help to check what might be the issue here & what kind of beads are recommended to be used for LM25117?

(The red boxes are where beads are applied. For FETs, beads are added to the source size)

Seems like that Mn-Zn and Ni-Zn beads have different impedance characteristics depends on the frequency

Regards,

  • 0
    TI__Guru 58671 points

    Hello David 

    It is not preferred to add beads. We recommend customers to optimize PCB layout or slowdown switching speed in order to minimize EMI.

    Since the OCP is triggered by the voltage at CS-CSG, please make it sure that the CS-CSG traces are kelvin-connected to the sense resistors and routed in parallel without any other connection.  

    -EL

  • 0 in reply to EricLee
    TI__Intellectual 2285 points

    Hi EL,

    Apologies for not keeping this updated.

    The customer just got back to me today and mentioned that they found the CS-CSG voltage was actually lower than Vcs(TH) during the event, meaning that the Vout drop issue could be caused due to other reasons.

    I think the customer's measurement might not be accurate, but assume OCP was not the reason, is there any other possible reasons that could cause Vout drops similar to OCP response?/

    Regards,

  • 0 in reply to David Huang
    TI__Guru 58671 points

    Hi David 

    First, please make it sure that the converter works well without the beads. If the converter doesn't work as expected after adding the beads, probably the issue is caused by OCP as you mentioned. Other possible cause is a malfunction due to a shoot-through. Please check if the deadtime is enough after adding the bead and also check if any dV-dT induced turn-on issue when the high-side MOSFET turns on. 

    -EL