TPS56628: TPS56628DDA 5V to 3.3V problem

Hi, Seems can’t see your sch picture, can you re-upload?

Yuchang

Hello,

Yes sorry. Here are the schematics.

My circuit:

WEBENCH Circuit:

Thank you.

Hi, schematic looks well, just suggest to add one more 22uF output cap, and this should not cause no Vout.

Did you check Soldering? And how many boards did you test? Are they same result?

Did you test the VIn/EN/VReg5/SW waveforms?

And also Please capture your layout pictures for reference.

Yuchang

Hello Yuchang,

First, thank you for your help!

Here are my answers:

1-Did you check Soldering? Yes soldering is fine

2- And how many boards did you test? Are they same result? We have 4 boards, but there is a modification we have to make before the board works. We did it for one board, but not yet for the others. Once it is done, we will test the other boards too

3- Did you test the VIn/EN/VReg5/SW waveforms? So the boards are at my client's, so I don't have access and they don't have an oscilloscope (sorry). But I did get the values

- VIN=5.07V

- EN = 4.94V

- VREG5 = 5.03V

- PG= 0V

- SW= 0.64V

- VBST=5.7V

- VFB = 0.16V

4- And also Please capture your layout pictures for reference

I am thinking that the problem might be in the startup of the DCDC, but we obvioulsy need an oscilloscope to check that. So I will be able to check it when the client sends me a board to test on my own (or if they buy an oscillo).

Thank you again.

Best regards,

Hi,

Layout is really not good, especially for the input and Ground. My suggestion is

For layout

You can try to jump short and strong wire line from GND pin to output cap GND and input cap GND. If thermal pad can be connected, it is better.

Make input line stronger, the line from input cap to pin is narrow and looks it is only one via connected to 5V? If so, jump a strong wire line to 5V from the input cap directly.

For waveforms

VIN/SW/Vout still need to be tested

Yuchang

Hello Yuchang,

Thank you for your help.

For the Ground, just a clarification. Apart from the GND internal plane, there are GND polygones recovering the whole board (as much a possible) both on the TOP and BOTTOM side that are not shown in the image. But I guess it  is more for shielding purposes.

We will try this solution in the next few days, I'll post back the results, and the waveforms when we get them.

Thank you again!

Best regards,