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TPS628503-Q1: Questions on Fsw and Switching Node Waveform

PY (Pengyu) Song
Expert 5860 points
Part Number: TPS628503-Q1

Hi team,

  1. How Fsw is measured - at SW node? 
  2. Does the Fsw tolerance include spread spectrum? Measured Fsw with spread spectrum enabled seems to exceed the min/max as below. Is this expected? 
  3. Is there any way to reduce below spikes? 

  • +1
    TI__Genius 12200 points

    Hello PY song,

    The right way to measure the SW node is to use a probe like this:

    I helps to avoid large grounding loops.

    Also, with respect to layout, it is always best practice to have small SW node plane and also to keep the away from the sensitive feedback signal path.

    Following app note (https://www.ti.com/lit/an/slva494a/slva494a.pdf) explains this in detail.

    "Does the Fsw tolerance include spread spectrum? Measured Fsw with spread spectrum enabled seems to exceed the min/max as below. Is this expected? "

    If tied to Vin, you have to include variation of upto 280kHz because of spread spectrum.