Buck converter Layout Review

[George]

Hey All,
I've been designing a PCB for a buck converter. Initially i had all the components on the top side but after watching Roberts discussion with Rick about this specific topic. This had me redesign the PCB with the controller and its passive components on the bottom leaving the power components on the top.

It would be interesting to see what everyone has to say about the layout. Also i can't makeup my mind if i should leave the AGND and Powere GND separated ?

Thanks in advance.

George

[George]

This should be a better layout. Moved the power components further down located on the top side thereby giving more room for the buck controller and passive components for routing traces at the bottom. Thinks i will stay with this rather than previous.

[qdrives]

(Some) passives are in the loops too, so it is better to have them on the same side as via's have a large inductance and may cause the return plane to change.

[George]

Can you please be more specific, what other passives are they ?

[qdrives]

Both the input and output capacitor, and the inductor.

[robertferanec]

George I agree with qdrives
PS: It would be useful if you always also attach a few screenshots, it is easier and faster for people to check

[George]

The Cin and Cout are on the top side together with the inductor & mosfets. The caps for BOOST are at the bottom near the IC at the bottom.

[robertferanec]

I tried to find a reference board, but could not find anything. There are some notes about PCB layout in the datasheet, but I guess you followed these.

PS: I would probably place it a little bit differently (for example I would maybe rotate the inductors and placed the output capacitors a little bit differently), but I am not expert for switching power supply designs, so do not take my words too seriously.

[George]

Yea the datasheet is my guide as of now. Still have the GND planes isolated tho the components are far apart. Not sure if should have single GND plane here as suggested by Rick in your talk with him.

When you said rotate the inductor i guess you meant rotate in a way that the CAP+ are closer to each other. Would it make any difference ? Its first time with a 4 layer PCB and my stack-up is Signal-GND, Signal-GND.

[robertferanec]

When you said rotate the inductor i guess you meant rotate in a way that the CAP+ are closer to each other.

I would maybe consider to have GND of output capacitors closer to GND of the transistors. But I am not expert for power supply design, I am not sure if that would make difference. It just looks to me like minimizing the loop, but it may not be necessary ... the best would be if someone who is experienced in power supply design would provide an opinion.