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TLV62090 facing problem to achieve the Cross over frequency

Utkarsh Srivastava
Prodigy 40 points
Other Parts Discussed in Thread: TLV62090

Hi ,

We are using 1.2V Buck converter IC TLV62090,Switching frequency is 1.25MHz, And there is no compensation network  available to tune the phase Margin.

We are facing problem to achieve the Cross over frequency as the desired frequency is 1/10 of 1.25Mhz i.e around 120Khz but we are getting 24Khz only by changing the feed back resistors R334=150kOHM'S and R335=75Kohm's.

Please find the Schematic for reference.

 

Please Suggest what needs to be done to achieve the desired cross over frequency.

 

 

 Regards,

Utkarsh

  • 0
    TI__Guru**** 150750 points
    Your schematic didn't seem to come through. Can you try again?

    Why do you need a certain crossover frequency?

    Did you measure it as shown here: www.ti.com/.../slva465a.pdf
  • 0 in reply to Chris Glaser
    Prodigy 40 points

    Hi Chris,

    It's our client requirement that the cross over Frequency should be in between 1/8 to 1/12 of the switching frequency and for IC TLV62090 Switching frequency is 1.2Mhz so we are taking 1/10 of switching frequency 1.2Mhz i.e around 120Khz.

    But we are able to achieve maximum of 24Khz only please suggest.

    Please find the attached SCH for Reference.

    Regards,

    Utkarsh

  • 0 in reply to Chris Glaser
    Prodigy 40 points

    Hi Chris,

    It's our client requirement that the cross over frequency should be in between 1/8 to 1/12 of the Switching frequency . For IC TLV62090 the Switching frequency is 1.2Mhz ,we are taking cross over frequency 1/10 of the switching frequency i.e 1/10 of 1.2Mhz =120Khz.

    but we are getting maximum 24Khz only. Please suggest.

    Please find the attached SCH for reference.

    Regards,

    Utkarsh

  • 0 in reply to Chris Glaser
    Prodigy 40 points
    Hi Chris,
    It's our client requirement that the cross over frequency should be in between 1/8 to 1/12 of the Switching frequency . For IC TLV62090 the Switching frequency is 1.2Mhz ,we are taking cross over frequency 1/10 of the switching frequency i.e 1/10 of 1.2Mhz =120Khz.
    but we are getting maximum 24Khz only. Please suggest.
  • 0 in reply to Utkarsh Srivastava
    TI__Guru**** 191445 points
    Generally speaking the crossover frequency for these type devices is not adjustable. You can get some extension with the use of a feed forward capacitor, but with 1.2 V output you will not get much additional BW. Why does your client have such a requirement? Fco of 1/8 to 1/12 Fsw is generally just a rule of thumb. So long as Fco << Fsw/2 there should be no issue.
  • 0 in reply to Utkarsh Srivastava
    TI__Guru**** 150750 points
    Yes, I agree with John. The BW is usually not important. It is more important to meet the time domain transient response target for output voltage drop, etc.

    As well, based on the location of the 0 Ohm resistor, you are not measuring the loop correctly. The app note I sent earlier shows the correct way to measure it.

    Finally, with such low FB resistors, you will likely need a much larger feedforward cap to see any effect. www.ti.com/.../slyt469.pdf