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TPS62135: Output ripple of TPS62135

Roy Chou1
Genius 16055 points
Part Number: TPS62135

Hi All,

My customer would like to design a DCDC for ther application.

Output spec is needed <3mV ripple noise. I checked  the passive device value and simulate in WEBENCH.

They both could achieve target.  They also has instrument could measure the 1mV voltage.

I understand the spec is critical, could above information guarantee the output noise <3mV 

And what factor should we concern? below is the schematic.

  • 0
    TI__Guru**** 191445 points

    Roy,

    I think you will find that difficult to achieve in real life.  For a basic switching regulator such as TPS62135, I think 7 - 10 mV os ripple at the switching frequency is about the best you will see.  And that is not including any switching noise.  Also during PFM operation the ripple will be higher.  To achieve lower output ripple, a post filter or LDO will be required.  We do have a new device coming out later this year that may meet that specification, TPS6291x.  What is your time frame?

  • 0 in reply to JohnTucker
    TI__Genius 16055 points

    Hi John,

    Thank you for your reply. But I still have a question, I used out ripple voltage formula to calculate its value. It showed the ripple could under the 3mV.(generated by switching noise) But you said "I think 7 - 10 mV os ripple at the switching frequency is about the best you will see.  And that is not including any switching noise."

    So what factor may cause 7-10mV ripple?(Assume L/C is ideal and no ESR/DCR) and their percentage. (IC/probe/......?)

    Roy

  • 0 in reply to Roy Chou1
    TI__Guru**** 191445 points

    Roy,

    i suppose if you are considering ideal modeling with no losses, ESR or ESL, then you can calculate a small number for ripple.  I have been working with switching regulators for more years than I care to recount and can tell you from experience, you will not do better than 7-10 mV without a a secondary filter or LDO follower.

  • 0 in reply to JohnTucker
    TI__Genius 16055 points

    Hi John,

    Thank you for your suggestion. I will tell customer. Do you have 2 stage filter design for dc-dc buck converter? (prefer TPS62135)

    Roy

  • 0 in reply to Roy Chou1
    TI__Guru**** 191445 points

    Roy,

    The LC filter will give 40 dB/decade of attenuation after the corner frequency.  Set the corner frequency to give the attenuation required.  Although for your application i would probably recommend an LDO follower.