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TPS62136: Power supply oscillating

Elder Costa17
Expert 2825 points
Part Number: TPS62136
Other Parts Discussed in Thread: TINA-TI, TPS62135,

The simulation shows the power supply below oscillates (~150kHz). Apparently the controller is not able to handle the high capacitance load at the output. Is there a way to stabilize this power supply? FWIW, simulation with lower ouput voltages was OK for the same load.

TINA-TI file attached.

Thanks in advance.

Fonte +VAMP-10V-2.TSC

  • 0
    TI__Guru**** 151530 points
    Hi Elder,

    It is likely the second stage filter that is causing the instability. Can you remove it and try again? See also this blog for a good discussion of this topic:
    e2e.ti.com/.../design-a-second-stage-filter-for-sensitive-applications
  • 0 in reply to Chris Glaser
    Expert 2825 points
    Hi, Chris.

    Thank you for the quick response.

    It works fine without the second stage: no oscillation on the simulation without the output LC. It also works fine with lower voltages (I simulated a 7.5V version of this supply) so the extra gain puts the supply into an unstable region.

    The problem is the bulk capacitance of the rail where this supply is bein used is high and sensitive to noise.

    Thank you for the link to the blog, I will take a look at it. Also any further suggestion that occur to you or anyone following this thread to stabilize the supply is welcome.

    BR

    Elder.
  • 0 in reply to Elder Costa17
    TI__Guru**** 151530 points
    Hi Elder,

    Aside from what is written in the blog, you might try adding some ESR to the large output cap. You can also move to the TPS62135 and use a 1uH inductor.

    Do you have a specific noise requirement from your load?
  • 0 in reply to Chris Glaser
    Expert 2825 points
    Hi, Chris,

    Again, thank you for the extra inputs.

    I am still working on the subject.

    I looked at the blog more closely and estimated the value for the resistor in parallel with the 100nF inductor but it was not sufficient to cease the oscillation on the simulator.

    A feed forward capacitor did the trick though. I am now reading the app notes referred in the data sheet do calculate the optimum value for Cff. I am also doing the math indicated in the blog to find the best value for the components.

    When I get to a conclusion I will post a follow-up on it.

    I will take a look at TPS62135. TI's portfolio is huge, which is good, but it is very easy to get lost in the middle of so many alternatives. :)

    BR.

    Elder.

    PS: I posted another message early today as I had an unexpected switching frequency when I simulated this power supply; I will assume the stability is not affected by this result, for the time being.
  • 0 in reply to Elder Costa17
    TI__Guru**** 151530 points
    Hi Elder,

    Yes, a Cff could help give you more phase.

    TPS62135 and TPS62136 are pin to pin.

    Nope, stability is not changed by whatever the frequency turns out to be for your application.
  • 0 in reply to Chris Glaser
    Expert 2825 points

    Hello, Chris,

    As a follow-up, I followed the notes to determine best feedthrough capacitor. I also added a low value resistor (0.2R) in parallel with the output inductor as suggested in the blog. With both I was able to obtain a stable solution on the simulator.

    Thank you very much for your support on this matter.

    Elder.

    PS: I have a follow-up question on TPS62135. I will post it as a separate question or open a follow-up topic.