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TPSM365R6: Output ripples and oscillations

Lukasz Antczak
Prodigy 10 points
Part Number: TPSM365R6

Tool/software:

Hi,

I have a problem with the TPSM365R6. The 5V output voltage oscillates like on the oscillogram below.

The input voltage range is 12-48V. The oscillograms were done with 25V on the input.

Here is the scheme:

The load is the MCU and some digital peripherals, with the LDO to make 3V3.

Layout:

top

2nd layer - gnd

3rd layer:

bottom:

I suspect that the connection of the 5V to the FB line by the via to the 5V polygon may cause problems. Do you think that a shorter connection directly to 5V output pad could solve the problem?

The converter is unstable. It helped when we initially changed the capacitors from 10u to 22u, which reduced the oscillations, but the problem wasn't solved. Three additional 22u capacitors didn't change the behavior—we observed a small, insignificant improvement. What can be the reason? The power supply is a good-quality bench supply; we also tried with the battery.

What can be the reason for the oscillations and how to solve the problem? 

Best regards

Lukasz

  • 0
    TI__Mastermind 28110 points

    Hi Lukasz,

    Before changing the layout, how are you probing the output voltage? And have you isolated the converter to check if it is isolated to the TPSM365R6 and not anything related to the load?

    Yes, a possibility could be by making sure the trace connecting the FB pin to the bottom feedback resistor should be as short as possible. The upper feedback resistor trace could be longer. 

    Let me know how it works out,

    Richard