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Original question:

TPS63802: The output voltage's ripple and noise is too large, how to reduce it?

TPS63802: too much noise on output

Tuan Pham
Intellectual 645 points
Part Number: TPS63802

Hi TI experts,

We are using TPS63802 in our design and experiencing huge noise on the output.

Schematic:

Layout:

There were few mistakes in layout where we placed the smaller capacitors away from the input and output of the IC, those points will be corrected in next layout. The next layer is fully ground.

Input is 3.8V, output is 3.3V, TPS63802 is in 3-cycles buck-boost operation.

I captured output ripple with proper probe setup, using probe tip and probe ground spring as short as possible (few millimeters only). The ripple voltage is only around 20mV which is very good, however there is huge high speed noise as you can see in below screenshots:

There is noise at the input as well, but half the amplitude.

I have tried added 100nF close to pin 6 and 10 of the IC, but it did not help.

Could you please give your comments? where is this noise from and how can we reduce it? This huge noise is coupling to our RF antenna and causing bad sensitivity performance.

Thank you very much.

  • 0
    TI__Mastermind 32350 points

    Hi  Pham,

    Most likely, that is not ture noise but some coupling between probe and noise source, such as high di/dt signal during your conduction loop switching.

    i think you can find that amplitude of this noise will change with different output current

    here is some advise

    • use a comxial cable but not a probe
    • test point should be as close as output cap

    actually, i think layout of output cap is not bad and no need to re-layout. 

    Regards

    Tao

  • 0 in reply to Tao Zhang
    Intellectual 645 points

    Hi Tao,

    Thank you for quick response.

    I did question myself that it is actually a noise or just a coupling from switching to the probe connection.

    I haven't tried using coaxial cable yet, here is how I did the probing:

    And below are some observations:

     - Noise increases with load current, as you said.

     - The output trace jumps to the other side of the PCB, and there I get noise as well, less amplitude but it is present there.

     - If I increase input voltage to 4.2V letting the IC runs in buck mode, the noise goes.

    So I am wondering what is going on. There should be some heavily switching in 3-cycles buck-boost mode, and if it is the switching noise coupling to the probe, then that noise can also coupling to other circuits nearby?

  • 0 in reply to Tuan Pham
    TI__Mastermind 32350 points

    Hi  Pham,

     - If I increase input voltage to 4.2V letting the IC runs in buck mode, the noise goes.

    that is right, during buck mode, high di/dt loop is much far away from probe, so it will be much better.

     i think you do not need concern about this noise. the coupling  coefficient between noise source and other circuit should be very poor. it is depend on distance ,direction and area. your layout about the loop is good enough.

    Regards

    Tao