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TPS23731: Reduce input ripple

Duong Tu
Prodigy 10 points
Part Number: TPS23731

Tool/software:

Hi Team,

Currently in my design, I measured a large ripple on the PoE input (800mV) and I want to reduce this ripple to below 500mV. Since my board space is not very large, I did not put a large capacitor at the input (on the design there is already a C94 capacitor with a value of 47uF/100V). I tried changing the value of the capacitors C248, C249 from 2.2uF/100V to 4.7uF/100V and I found that the ripple voltage decreased to only 540mV. So I want to ask:

1. Can I change the value of C248, C249 (see attached image) to reduce the input ripple voltage?

2. Do you have any better recommendations to reduce the ripple on this input?

Looking forward to hearing from you soon.
Thanks.

  • 0
    TI__Mastermind 37121 points

    Hi Duong,

    Thanks for reaching out! Sorry that PoE team is quite busy recently. I will try to get back to you by this week.

    Best regards,

    Diang

  • 0 in reply to Diang Xing
    TI__Mastermind 37121 points

    Hi Duong,

    Thanks for your patience. For input ripple, line inductor and capacitor are commonly used to reduce the ripple. But seems you already tried multiple values. A PI-filter is normally applied for reducing the ripple. 

    Besides, have you measured the phase and gain of your circuit? You may try to adjust the phase margin. Increasing the phase can help to slower down the response, and reducing the phase can result in faster response. And your input/output ripple could be changed sometimes. Between 45 - 60 degree is normally optimized.   

    Best regards,
    Diang