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TPS65400 Start up wave form at fsw=1MHz

tateo yamashiro
Guru 10890 points
Other Parts Discussed in Thread: TPS65400

Hi,

My customer has question about TPS65400.
Could you tell us about question?

[Question]
 My customer test start up performance under the following condition at EVM.

  channel: CH2
  Vin: 12V
  Vout: 1.05V
  Iout: 500mA
  fsw: 1MHz (I2C setting)
  other parts: EVM defult value

 Wave form is below.

 It is not normal.
 And when output is no load, output voltage is above 1.05V. It is not regulation.
 Could you tell us about resolution method?

Best Regards,
tateo

  • 0
    TI__Intellectual 2590 points
    H Tateo,

    would you please give us more detail wavefrom, including LX voltage and indcutor current?
    When Iout transient from heavy load to no laoding, it's normal output voltage is above 1.05v. When Iout transint form 0 to heavy loading, it's normal output voltage is under 1.05V.
    thanks!
    Eric
  • 0 in reply to Eric Guo1
    Guru 10890 points

    Thank you for your reply.
    This is including SW voltage and inductor current waveform.

    And EVM is under the following condition.

      channel: CH2
      Vin: 12V
      Vout: 1.05V
      Iout: 500mA
      fsw: 1MHz (I2C setting)
      L2: NR8040T2R0N
      R8: 3k
      R10: 10k
      C19: 470pF
      R35: 180k
      other parts: EVM defult value

    Best Regards,
    tateo

  • 0 in reply to tateo yamashiro
    TI__Intellectual 2590 points
    Hi Taheo,

    From your waveform, when the loading is coming, the output drops a little, it's normal operation for our device. You can measure the drop value of output to see whether this drop can be accepted by customer's system.
    BTW, our device's Min-on time is 150ns, so when vin=12v, vout=1.05V, the max frequency for TPS65400 is about 600Khz, so we don't suggest customer use 1Mhz for this application. Why customer need so high frequency? is there any special requirement?
    If need any more hlep, please let me know or send email to me eric-gou@ti.com.
    thanks!
    Eric