TPS54627: Output voltage much lower than expected

JD Peiffer

Prodigy 130 points

Part Number: TPS54627

Hello,

We are using the TPS54627 with an input voltage of 9.3V; however, we see an output voltage of 0.509V.

Referencing the data sheet, we are using:

R1: 30kOhm

R2: 22.1kOhm

R3: 10kOhm

C1,C2: 10uF

C3: 0.1uF

C4: 10pF

C5: 1uF

C6: 8200pF

C7: 0.1uF

C8,C9: 22uF

L1: 3.3uF

Interestingly enough, the output voltage varies with our input voltage, peaking at 0.736V out with 13.1V in. The same phenomenon happens on two chips we tried. Any ideas? Leads?

over 4 years ago

0 Yuchang Zhang over 4 years ago

TI__Mastermind 18510 points

Hi, Components value are ok, you can check EN and VREG5 works well or not firstly.

And meantime, please upload your schematic and layout for review.

Yuchang

0 JD Peiffer over 4 years ago in reply to Yuchang Zhang

Prodigy 130 points

Hi,

VREG5 maintained a steady 5.5V. The chip also responded as expected to disconnecting the EN pin (the output stopped).

Here is a schematic

circuitdraft.sch

0 Yuchang Zhang over 4 years ago in reply to JD Peiffer

TI__Mastermind 18510 points

C11, C12 is 22uF not pf, right?

If it is 22uf, please upload layout for check.

0 JD Peiffer over 4 years ago in reply to Yuchang Zhang

Prodigy 130 points

Sorry, that was a mistake in the schematic.

Those capacitors are 22uF in our breadboard. I will send pictures of the board if you would like.

0 Yuchang Zhang over 4 years ago in reply to JD Peiffer

TI__Mastermind 18510 points

Yes, if you are sure soldering and components are correct, please upload layout.

0 JD Peiffer over 4 years ago in reply to Yuchang Zhang

Prodigy 130 points

Yuchang,

Here is our breadboard. The labels reflect the datasheet labels. Our breakout board did not have the capability to ground pin 9, the power pad. Do you think this could be the issue?

Thanks,

0 Yuchang Zhang over 4 years ago in reply to JD Peiffer

TI__Mastermind 18510 points

From the picture, I can say it is bad layout. All components are DIP model, which have big parastic indutance and impendence. and the Ground loop should be bad as well. Basically I am sure the issue is caused by the bad layout. Recommend you refer to the EVM design to draw a PCB rather than breadboard. You should get the output what you want then.

Yuchang

0 JD Peiffer over 4 years ago in reply to Yuchang Zhang

Prodigy 130 points

Great! Thank you!

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TPS54627: Output voltage much lower than expected