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TPS54226 Inductor value

K. Sasaki14
Guru 10200 points
Other Parts Discussed in Thread: TPS54226

My customer is thinking they use TPS54226 on attached circuit condition.

They want to make output ripple level lower. So they increase inductor value to 10uH.

This value isn't in recommend component value table in datasheet.

Then is there any concern for device operation?

1018.TPS54226 2.5V 10uH.pdf

  • 0
    TI__Guru**** 191445 points

    In general, increasing the inductor value will not have much effect on the ripple.  These devices are intended for use with ceramic output capacitors.  Measured outut ripple at full load is already less than 10 mV p-p (see http://www.ti.com/general/docs/lit/getliterature.tsp?literatureNumber=slvu336&fileType=pdf)

    Raising the inductor value will lower the LC corner frequency and you will probably see reduced phase margin.  Phase cannot go to 0 so the device is inherently stable, but some users may be uncomfortable with PM less than 30 degrees.

    Also for the same package size, the higher value inductor will have higher DCR and operate in CCM at lighter loads so efficiency is less.

    I have tested a few designs with non-standard component values, but not your specific case.  I don't think you will have any issues other than what I recount above.

     

     

  • 0 in reply to JohnTucker
    Guru 10200 points

    Thank you for your answer.

    I think DCAP2 is hysterisis control and there is no need to consider the phase compensation.

    But is my idea wrong?

    Do I need to think about the phase compensation?

  • 0 in reply to K. Sasaki14
    TI__Guru**** 191445 points

    From an absolute standpoint, you do not need to be overly concerned with phase margin.  For pure hysteretic control, it is not possible to measure the loop response in the normal manner.  DCAP2 is adaptive on time, hysteretic off time control.  This topology has pseudo fixed frequency, so the loop can be measured.  It is inherently stable as the phase cannot reach zero until the frequency is above Fsw/2.  The recommended components are chosen so that the phase margin at crossover is optimized.  very large or very small output filer components may cause teh phase margin to be very low and allow some ringing in the time domain transient response.