TPS5410 Oscillation Issue

Paul Larson79737

Other Parts Discussed in Thread: TPS5410

Hello. I am designing a circuit to take 12V down to 3.3V by using a TPS5410. I am having some noise issues that I am trying to troubleshoot and cannot find the problem. I followed the datasheet to pick component values and I am getting a 1Vp-p oscillation as high as150MHz on the output. The voltage bumps up to about 3.3v, but the oscillation is too much. Here are the components I've used, which should match reference designators in the datasheet:

L1: 68uH, part number NR8040T680M

C1: 4.7uF, part number C3216X5R1H475K

C2: .01uF, part number GRM216R71H103KA01D

C3: 150uF, part number EEE-FP1V151AP

D1: Schottky, part number B340A-13-F

U1: TPS5410

R1: 10k, part number RMCF1206FT10K0

R2: 5.9k, part number 270-5.9K-RC

I've attached the schematic. Please note that the resistor on ENA is currently removed to use float-enable.

Can anyone help me? I can also grab a screen capture of the o-scope if needed. Thank you!

Paul

over 14 years ago

0 JohnTucker over 14 years ago

TI__Guru**** 191445 points

Do you have a waveform that illustrates your issue?

0 Paul Larson79737 over 14 years ago in reply to JohnTucker

Prodigy 40 points

Here is the signal with DC Coupling:

And here it is with AC Coupling:

I have 12V on the input, and a 165 Ohm load on it. Let me know if there is anything else you need. Thanks.

Paul

0 Paul Larson79737 over 14 years ago in reply to Paul Larson79737

Prodigy 40 points

You will notice too that I am having an even larger swing than I mentioned before. I rebuilt the board to ensure connections, and these are the waveforms for it.

0 JohnTucker over 14 years ago in reply to Paul Larson79737

TI__Guru**** 191445 points

So does that waveform repeat at teh switching frequency? IT probably does and is referred to as switching noise. There are very high slew rates associated with these dc/dc converters any stray inductance will cuase the waveforms you observe. Also, some of this might be due to your measurement technique. You should use "tip and ring" to keep te ground loop as short as possible and measure directly across your output cap. I can also recommend that you add some high frequency bypass to your design. maybe a 0.1 and 0.01 uF X5R or better ceramic capacitors. then measure the output voltage dierctly across the 0.01 uF cap, keeping the ground lead of your scope probel to less than 1 cm. If that is not enough you may need to consider an RC snubber from PH to ground. That will need to be tuned to your layout but you could start with maybe 3300 pF and 4.7 ohm in series between PH and GND.

0 Paul Larson79737 over 14 years ago in reply to JohnTucker

Prodigy 40 points

John-

I completely forgot about the ground wire length, which was my actual issue. It turns out my circuit works great, my measurement techniques were just wrong. Thank you for the help!

Paul

0 JohnTucker over 14 years ago in reply to Paul Larson79737

TI__Guru**** 191445 points

You're welcome...

0 Gary Norris over 12 years ago in reply to JohnTucker

Intellectual 300 points

Hello

I have a similar issue with my TPS5410. The attached waveform show what I get on the PH pin on 2 of my chips for different output voltages. As you can there is an oscillation in there. I have used the online tool and schematic and the recommended layout on my board also.

Thanks

ph53uin_.tif

0 JohnTucker over 12 years ago in reply to Gary Norris

TI__Guru**** 191445 points

There is not any time or amplitude scale in your wave form. There is low frequency oscillation that most likely is typical resonant ring during DCM operation, which is completely normal. There is also some high frequncy ringing on the top of the high side FET switching pulse. that is also normal. You may be able to decrease it with an RC snubber from PH to GND.

0 Gary Norris over 12 years ago in reply to JohnTucker

Intellectual 300 points

What kind of values would be needed for the RC snubber?

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TPS5410 Oscillation Issue