TPS563201: Very high output ripple of 174mV @ 5V and 122mV @ 3,3V

Hi Pascal，

Could you share us the schematic first? We will help check whether the parameters are reasonable. You can also check the LC table in Page13 in datasheet.

http://www.ti.com/lit/ds/symlink/tps563201.pdf

Best Regards,

Vinent Zhang

Thanks for the fast response!

The schematic looks like this:

I copied the design that was used on page 12 of the datasheet. I only switched the value of the voltage divider and the inductance, to the values i need for my application (looked them up on page 13). 

I could also upload a picture of the board layout if this would help you.

Hi Pascal，

The schematic looks fine, but I believe your circuit doesn't work normally. TPS563201 switching frequency is 580kHz but from your waveform shows the frequency 25kHz(3.3V rail) and 62.5Hz(5V rail). Are you sure these THT component are inductors? It looks like resistors...

Best Regards,

Vincent Zhang

Sadly these are inductors, but you are right about the switching frequency. When i measured the AC-component the frequency wobbled the whole time. It should have stayed at a certain value, right? 

I bought the following inductors:

http://www.electronicoscaldas.com/datasheet/HBCC-Series_Fastron.pdf (2,2µH and 3,3µH out of this series)

Best wishes,

Pascal

Hi Pascal,

What's your load current of your above waveform? For 0mA, the output ripple would be large.

Best Regards,

Vincent Zhang

These measurements above have been done with a load current of 250mA (i need this current for the application), but i also measured the ripple with 0mA load current and the results were nearly the same. I think the ripples for 0mA were ~80mV @ 3,3V and ~110mV @ 5V. I can remeasure it and upload the measurement if you want.

Best wishes,

Pascal

0mA ripple is about 80mV, it's reasonable because device workes in PFM mode then, but not make sense at 250mA condition, So far I couldn't address the root cause now so may need you to provide more waveforms.

1. SW and Inductor current waveform？

2. Layout picture.

Best Regards,

Vincent Zhang

1. I will try to measure the output current tommorow or at the start of next week in university. 

2. Is there a way to send you the board data or attach it to this post? I made a picture but it's not the optimal solution.

Here is the picture of my layout:

It's a two layer design with the second layer only beeing a ground plane. So one signal and one ground layer. On the signal layer are various power areas for all components that need direct voltage supply. On the bottom of the first layer is the dc power jack which provides 12V input for the dc/dc converters (not seen on this picture).

Best whishes,

Pascal