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.

TPS40400: TPS40400 minus40deg.C loadstep fequency change

Part Number: TPS40400

Dear all,

My customer want to know reason of phenomenon below,

Osc.Freq. was changed at Iout 0 to 40A load step.

Ta= 0deg.C and C8= 4700pF no change always 400kHz
Ta= -40deg.C and C8= 3300pF no change always 400kHz
Ta= -40deg.C and C8= 4700pF 400kHz->200kHz->400kHz

Customer want to use C8=4700pF because faster transient response.
Why this freq. change happen?

Thank you,
H.DOITPS40400 Freq..pptxcct.pdf

  • It appear to me that the BW is already very high and that by changing the component values as you have, has made your design marginally stable ans under cold conditions circuit is unstable. If a better transient response is required, suggest increasing Cout and decreasing Cout ESR.
  • TPS40400 -40degC.load step.pdfDavid-san,

    Thank you for your reply.

    My customer's End user is most Strict and BIG company in Japan  around Yokohama, TI assigned.

    End user found this problem and ask my customer "Why freq. down to 200kHz?"

    Then TI have to explain this phenomenon more detail.

    My customer checked  waveform , and found that   ferq. down -> OVP -> output down.

    Why freq. down at minus 40deg.C  0A to 40A Load Step?

    Thank you

  • This is a voltage mode controller.  And I think that the issue at cold with a load transient, is due to the impdence change in the output capacitor and loop compensation that has minimal phase margin.  When you run at cold, the loop goes unstable (slightly) with a load large load step you are seeing this issue.