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TPS5430 with a lots of ripple at the output

Sebastien Lassonde
Prodigy 10 points

Hi everyone and John Tucker,


For some reasons, in my newest PSU design, I read a lot of ripple at the output. At first, I thought it could be the ceramic capacitor at the output. We added the calibration circuit.


We used all the recommended components. Sumida inductor, X5R capacitors, followed the calculations, etc

You will see below that even without load conditions, the ripple is really high.
 We reused the layout from another board, we checked and measured on this previous board, and everything is fine. maybe there is a little detail on the layout.


Any advice would help.
 Thanks in advance

Sebastian

here is a screenshot of the top layer :


here is the bottom view :

Here is a few probing screenshot of the circuit :

here is two screenshot with 2 timebase:

Finally, here are BOOT and PH pins at full load 1.2A 3.3V out

PH pin first

BOOT pin now
 :

  • 0
    TI__Guru**** 191445 points

    What you are looking at is switching noise rather than ripple.  You have to be careful in measuring that.  I recommend measuring directly across your output ceramic capacitor using the "tip and ring" method or a short < 1 cm ground lead.  If you find it is still too much you may need to consider an RC snubber from PH to GND.  I can send you the instructions for calculating the component values.

  • 0 in reply to JohnTucker
    TI__Mastermind 35165 points

    In addition to the snubber, the placement of the input capacitors is important to reduce the switching noise. There should be a short low inductance connections in the critical loop made by the input capacitors, integrated high-side FET and schottky diode. Specifically on this layout there is a relatively long path between the GND of the input capacitors and the GND of the schottky diode which leads to more inductance. The connection could be significantly shortened if the diode and input capacitors were rotated 180 degrees.