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TPS63070: Output ripple becomes larger when Vin is close to Vout

reuven.goldshtand
Prodigy 50 points
Part Number: TPS63070

Tool/software:

I use TPS63070 as buck boost for Vin from 2.4V to 13.2V. Vout 3.3V. Output current 0.4A.

Inductor is COILCRAFT XGL4015-102MEC.

Below scope capture of output current and voltage of TPS63070 When Vin decrease from 3.8V to 2.8V.

When Vin reach 3.5V output current  p-t-p start to increase and output voltage ripple also increase.

 

I changed inductor to COILCRAFT XFL4020-472ME and output voltage ripple and current p-t-p decreased.

Below capture with inductor 4.7uH.

Are there is limitation for maximum inductance and DCR for the inductor that can be used for my application?

  • 0
    TI__Mastermind 32350 points

    Hi,

    Could you Zoom in the ripple your got?

    When Vin is closed to Vout, device will work in BUBO mode and for this device, this mode has some low frequency ripple which should has no matter with inductor.

    Recommend inductor as below.4.7uF is out of spec.

    Regards

    Tao

  • 0
    Prodigy 50 points

    Hi,

    1. On data sheet is written "If the operating conditions results in a frequency of the RHPZ of less than 400kHz, more output capacitance should be added to reduce the cross over frequency."

    Can I add capacitance for working on frequency RHPZ less than 400Khz?

    2. On data sheet is written "Device stability should therefore be observed mainly under these worst case operating conditions."

    I test device with 4.7uH in my card and is working well. Can I use 4.7uH?

    Are there is other tests that I need to do to be sure I can use 4.7uH?

  • 0 in reply to reuven.goldshtand
    TI__Mastermind 32350 points

    Hi  Reuven,

    Yes, more Cout can help to reduce your bandwidth of loop.  If no loop stability issue observed from your side, i would like say yes for 4.7uH inductor.

    Besides normal tests, you should have a Bode plot test to make sure loop is ok, if no loop analysis tools is available, please try use load transient test instead.

    Attachment below is for ripple measurement and how to evalute loop stability by load transient tests.

    ssztb25.pdf0827.slva381b.pdf

    Regards

    Tao