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I am working on a project using a TPS54202H switching regulator.

The power supply is currently in 12V DC @ 60mA and am expecting a 5V output.

I followed the datasheet schematic but when I power it up I am receiving a square wave at the output that peaks at about 200-300mV. The square wave is telling me that there is some capacitor interference (I believe,) but I am not sure how to fix this.

I am currently stuck and not sure where to go from here.

Reference Design Datasheet Reference Design

Schematic Schematic Design

PCB Layout PCB Layout

Output Output

Components used: L1 C4 C5 & C6 C7 & C8 C9

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  • \$\begingroup\$ Looks like a trickle protection, you are probably pulling too much current. Have you tried without any load? Your traces are way too thin, that might be an issue as well \$\endgroup\$
    – Damien
    Mar 5, 2021 at 17:56
  • \$\begingroup\$ Power supply is currently drawing 60mA @ 12V. Sorry I should have said that in the initial post \$\endgroup\$
    – kpjesk
    Mar 5, 2021 at 17:59
  • \$\begingroup\$ Please post a list of used components, eapecially the inductor make/model to figure out its parameters. I have to agree with Damien though, the component layout and wiring between them unfortunately does not look how a layout and wiring of a switch mode converter should look like. \$\endgroup\$
    – Justme
    Mar 5, 2021 at 18:42

4 Answers 4

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This converter has a constant peak inductor current of as much as 3.9A in normal operation.

Your inductor looks suspiciously small. Check the saturation current and/or substitute a Würth 7447714150 with 4.1A typical saturation current, as used in the evaluation board.

It will not fit your existing PCB layout. Probably nothing that will work will fit. Which is okay, since it needs significant improvement anyway.

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Your inductor is wrong! TPS54202H Datasheet lists 15μH and you show 15μH in your schematic.

While referenced inductor data sheet for L1 lists 1.8 ~ 1000nH, which is a maximum of 1μH.

enter image description here

Since you don't identify the actual inductor, it is probably 15nH. You have 1000'th the inductor required!

Note size of inductor compared to TPS54202 from TPS54202HEVM-716 Evaluation Module.

enter image description here

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Looks like a trickle protection, you are probably pulling too much current. Have you tried without any load? Removing big caps on the rest of the pcb?

Your traces are way too thin, that might be an issue as well, especially switch pin 2 should be a fat thick and short trace as well as the LC node and the filtering cap. Same goes for input caps.

Check the data sheet layout and compare to yours: enter image description here

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Just remembering, you have to put most of these PWM chips under load or they throttle back like this. Try adding a load at least 50% capacity (80% ideally) and try again.

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  • \$\begingroup\$ Interesting @Transistor, you chimed in. Where you going to try to change my answer? Because you didn't change anything.... \$\endgroup\$
    – David Mikeska
    Mar 26, 2021 at 18:26
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    \$\begingroup\$ Oh yes I did. I fixed the capitalisation of your PWM initialisation (bad boy). You can always track changes by clicking the "edited ... ago" link. Welcome to EE.SE. \$\endgroup\$
    – Transistor
    Mar 26, 2021 at 18:29
  • \$\begingroup\$ You must be an moderator or someone who is picky about English like a teacher. @Transistor Yes,I'm new to the site, but not new to electronics. Back when PWM was born into existence, and at the time I was a RCA tv repairman, the way we were taught to load the PWM supply in the TV was to use a light bulb. I imagine they could do the same using an automotive tail light. \$\endgroup\$
    – David Mikeska
    Mar 26, 2021 at 18:45
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    \$\begingroup\$ Maybe like a teacher who believes in clarity of communication in a world of falling standards. Have fun. \$\endgroup\$
    – Transistor
    Mar 26, 2021 at 19:17

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