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TPS54239 - Ringing on 5V output

Other Parts Discussed in Thread: TPS54239


I ordered a sample of TPS54239.

My requirements are:

Input 12V; Output 5V; Imax = 1A

For testing purposes I soldered all required components together on a little board. All connections as short as possible (e.g. VFB). All grounds connected without a ground plane. Now I can see a repetitive disturbance on the 5V Output Voltage (see attachment). The periodic time between the ringing is 2us and the signal itself has a time period of 7,5ns.

What is the reason for this disturbance?


S. Hilgers

  • You are seeing ring ringing voltage from the switching node.  You will find that layout and tight grounding are essential for proper performance.  I would suggest teh you order the EVM to evaluate your circuit on a proper printed circuit board.  That said there will always be some switching noise on your output due to the very fast di/dt of the switching FETs and stray inductance in the circuit.  It may seem worse depending on how you measure it.  You should use "tip and ring" approach directly across one of the output capacitors or a short ( < 1 cm) ground for your probe.  You can limit it more by using an R C snubber from SW to GND.  Also some small value output capacitance in parallel with the main output capacitors can help (0.1 uF, 0.01 uF and 0.001 uF) will provide a broad frequency span of low impedance path to ground for high frequency noise.