How to layout the ground planes below a buck converter?

[MarkS]

I've included a switching regulator in a project, just because I've never used them before and this will be a useful component to have under my belt. I followed Phil's Lab's wonderful YouTube videos on how to layout the components and that was incredibly useful, but he really didn't go over ground planes directly under the high frequency components. I figured that capacitively coupling the high frequency to ground would not be a good thing, but made that decision out of ignorance. This is a 4-layer board with the inner two layers being ground and the bottom layer being power/signal. The top layer has a small ground plane with stitching vias, although I have a vague recollection of hearing of potential EMI through capacitive coupling in microstrip layouts in a YouTube video, so this may be bad practice.

I'm using the Richtek RT8259 regulator and the component selection is an exact copy of the datasheet's typical application circuit to get a 3.3v output, plus some reverse protection components.

I've included screenshots of the top, second (third layer is the same) and bottom layers of the regulator layout. I'd love a critique and advice here.

[T3sl4co1l]

Why would you remove ground under the switch node, exactly where it does the most good (reducing height of traces above ground, minimizing loop inductance)?

You also show only +3V3 under that area, which isn't connected to anything else at all, it's a dead end and no point to pour over the board.  Board isn't big enough to provide capacitance value (it'll be what, 100pF if that?), nor would it be connected to anything where that would matter.

Plane capacitance is a factor in the 10MHz+ range, where local IC bypass dominates, and for which plane can substitute.  This is all for naught behind even some inches of hookup wire (20s of nH)), and it looks unlikely you'd have such an intimate connection [as inner planes] from this board to another.  (And, further assuming your load is one where such high-frequency bypassing matters; many don't.)

This would be materially improved, actually, if reduced to 2 layers -- pouring GND fully on bottom and nothing else.   Height above GND can be tweaked by choosing a thinner board, if you like (0.8-1mm, or even less really), but I doubt it matters here.

Tim

[MarkS]

Why would you remove ground under the switch node, exactly where it does the most good (reducing height of traces above ground, minimizing loop inductance)?

That's why I'm asking.

You also show only +3V3 under that area, which isn't connected to anything else at all, it's a dead end and no point to pour over the board.  Board isn't big enough to provide capacitance value (it'll be what, 100pF if that?), nor would it be connected to anything where that would matter (plane capacitance is a factor in the 10MHz+ range where local IC bypass dominates, and to which plane can substitute).

This is just the regulator portion of the PCB. The bottom plane covers every component needing 3.3v, it's just not shown.

[selcuk]

I recommend to check out this youtube video as well:

[youngda9]

I recommend to check out this youtube video as well:

Excellent video!  Thank you for sharing.