• State TI Thinks Resolved
  • Locked Locked
  • Replies 4 replies
  • Answers 1 answer
  • Subscribers 63 subscribers
  • Views 362 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.

LM27342: EMC comply problems

Francesco Da Re
Intellectual 260 points
Part Number: LM27342

Hello, we are facing unexpected EMC problem with this component.

We have followed all the common design rules but we found 2 MHz harmonics (the switching frequency, of course) everywhere.

Pcb is a 4 layer with standard power planes in the middle layers. Any suggestions?

Francesco

  • 0
    TI__Mastermind 35115 points
    Hi Francesco,

    Are you debugging a radiated noise or a conducted noise problem? Also is there a specific standard you are trying to meet or is it noise affecting some other components performance?

    I may also need to take a look at your schematic and PCB layout.

    Since the noise problem is related to harmonics of the switching frequency, an input LC filter might be needed to help filter out the noise going back onto the input rail. This mostly reduces conducted noise but can also help with radiated noise. The app note linked below is a good reference for input filter design that might be useful.

    www.ti.com/.../snva489c.pdf

    Best Regards,
    Anthony
  • 0 in reply to Anthony F
    Intellectual 260 points

    Hu Anthony,

    we are debugging radiated noise.

    In the meantime I re- runned TI WEBENCH design tool. I saw that, for my power supply range the tool do not place the diode on the BOOST pin.

    Removed that diode the radiated noise is much lower! Now it should be below limit.

    Thank you

  • 0 in reply to Francesco Da Re
    TI__Mastermind 35115 points
    I'm glad you find a solution to this. For future reference, can you share what voltage were you charging BOOST from initially?

    I will guess it was higher than the internal 3.9 V BOOST LDO. I am guessing it was higher because higher BOOST-SW voltage would cause the HS FET to turn on more quickly resulting in faster edges at the SW node.
  • 0 in reply to Anthony F
    Intellectual 260 points

    Anthony, it was 5V0.