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About fsw of LMR14020/14030Q1

tsuyoshi tokumoto
Expert 2630 points
Other Parts Discussed in Thread: LMR14020, TS5A3166

Hello team,

  I have a question about LMR14020Q1/14030Q1.

  My customer would like to change the fsw frequency by switch under the conditions
  that the EN signal is high(LMR14020Q1/14030Q1 is active).
  
  I attached a current circuit plan.
   *Cf. attached file lmr14020_30Q1_Rtclock.xlsx

5850.lmr14020_30Q1_Rtclock.xlsx

Question)
  Is the such usage possible?
  If possible, what percentage can the switching frequency change?
   
Best regards.
Tsuyoshi Tokumoto
 

  • 0
    TI__Genius 16410 points
    Hello Tokumoto-san,

    Please let me move this to the Non-isolated DC/DC forum. They should be able to answer your question.

    Regards,
    Karl
  • 0 in reply to Karl Wallinger
    TI__Guru**** 191445 points
    Actually, this should go to the Simple Switcher forum...
  • 0
    TI__Genius 16025 points
    Hi Tsuyoshi,

    Thank you for your question. I'm forwarding this to the Apps team in charge of the part. They will get back to you very soon.

    Thanks,
    Anston
  • 0
    TI__Intellectual 2790 points
    Hi Tokumoto,
    This application circuit should be feasiable. But make sure the leakage of the switch is lower enough ( much lower than 1uA)
    we can't guarantee how large is the frequency variation of such application. For resistor around 11kohm with 0.1% accuracy, the variation is about 6%.
    BR
    Luke
  • 0 in reply to Luke Pan
    Expert 2630 points

    Hello Luke_san

    Thank you very much for your prompt reply.

    I am concerned that the change of fsw by RT resistances under the condition
    that LMR14020Q1/14030Q1 is working affects the Vout voltage.

    Am I correct in thinking that the Vout voltage is not affected by changing
    the fsw several percent,even if LMR14020Q1/LMR14030Q1 is working?

    In additon,the TS5A3166 has very low leakage current feature(20nA:Max),
    and I will calculate the fsw variation by the variation in resistances value of RT.

    Best regards.
    Tsuyoshi Tokumoto

  • 0 in reply to tsuyoshi tokumoto
    TI__Intellectual 2790 points

    Hi Tokumoto,

    With such small frequency transient (1.998MHz-2.099MHz), the Vout over/undershoot during the frequency transient will be super small. maybe only several mV with normal Cout.

    BTW, what's ctm's application with such small frequency transient?

    BR

    Luke

  • 0 in reply to Luke Pan
    Expert 2630 points

    Hello Luke_san,

     Thank you very much for your prompt reply and advice.

     The application is car infotainment system.

     He is concerned that the EMI by the higher harmonic component of fsw
     affects FM band.

     That is one of the measures to reduce the influence on selected channel even a little.

     I understand that the method of changing fsw by changing some resistance values
     does not have a big influence on the Vout from your reply.

     Therefor I think that it is possible to change the fsw 10 percent.

     Is there any problem?

    Best regards.
    Tsuyoshi Tokumoto

  • 0 in reply to Luke Pan
    Expert 2630 points

    Hello Luke_san,

    Thank you very much for your prompt reply and advice.

    The application is car infotainment system.

    He is concerned that the EMI by the higher harmonic component of fsw
    affects FM band.

    That is one of the measures to reduce the influence on selected channel even a little.

    I understand that the method of changing fsw by changing some resistance values
    does not have a big influence on the Vout from your reply.

    Therefor I think that it is possible to change the fsw 10 percent.

    Is there any problem?

    Best regards.
    Tsuyoshi Tokumoto