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TPS62816-Q1: Low-Frequency Noise and Ripple

Martin M.
Prodigy 170 points
Part Number: TPS62816-Q1
Other Parts Discussed in Thread: TPS62816EVM-140, TPS62913

Hello

I'm currently evaluating the TPS62816-Q1 part with the evaluation board TPS62816EVM-140. In our application it should supply noise sensitive ADC/DAC supplies. I made a ripple and FFT measurement of the output voltage which raised some questions. Please check the scope screen shot below.
 
The output voltage on the eval. board shows a peak-to-peak ripple of appr. 1.1mV (corresponding to the -69dBVrms peak at 2.225MHz). For our application we'll need to further reduce the output ripple by adding a second stage filter. Now the questions:
1) In the second screen shot you can see the waveform of the output voltage and the FFT. The signal shows some low frequency noise/ripple with appr. 2mVpp. It's also visible in the FFT below 1MHz. What causes this noise? Is it already wideband noise / flicker noise / etc. as described on the following references?

https://www.ti.com/lit/wp/slyy134/slyy134.pdf
https://www.analog.com/en/technical-articles/comprehensively-understand-and-analyze-switching-regulator-noise.html

2) Is there a way to reduce this noise or is it caused by the converter and it's internal circuitry itself?

Thanks in advance for any help!
Regards, 
Martin

  • +1
    TI__Genius 14876 points

    Hello Martin,

    What you are observing seems to relate more to what was described as WideBand Noise.

    In order to minimize its impact, I would see different way to address it.

    You would indeed have a shot by using a second stage filter. 

    Also, using some larger 47uF caps would allow you to filter under 1MHz, but this would effect only a small portion of the spectrum as you can see below (as an example):

    Some TI DCDC converters were designed specifically to address those type of very low noise and low ripple applications.

    TPS62913 was for instance designed to address those challenges. Though, 3A max output current may not be enough for your design.

    I recommend you to have a look at the following paper, snva871. This is a good read for your topic.

    To answer your last question, this is caused by the converter and it's internal circuitry but we can try to minimize its impact.

    Let me know if you have any questions.

    Thanks a lot!

    Regards,
    Dorian 

  • 0 in reply to Dorian Brillet de Cande
    Prodigy 170 points

    Hi Dorian, 
    Thanks for the information. This helps a lot.

    The TPS62913 looks very interesting from the first glance, I'll check on that. Is there any similar part you can recommend with 6A output current capability?

    Best regards,
    Martin

  • 0 in reply to Martin M.
    TI__Genius 14876 points

    Hello Martin,

    I haven't heard of any project going this direction but I will check with the relevant people and come back to you as soon as I get the information.

    Thanks a lot!

    Regards,
    Dorian