Power Planes

[m00dawg]

I can't recall any designs here that make use of power planes (may just have not noticed) but I was curious as to what the use case might be? I'm a little confused, for instance, how useful decoupling capacitors end up being when using a plane. It seems like a pretty clever idea but since I don't see if often used in designs I've seen, and since I haven't found too much online about the subject (from Googling anyway), I thought I would ask.

Thoughts?

By the way, sorry for all the Design Concepts posts! Sure am learning quite a bit! The help is much appreciated!

[Shuriken]

I think i am familiar with the design concept. But so far i have only seen it in switching psu designs. Not sure what the purpose is.

[m00dawg]

As best as I can tell, it's to control impedance and has some capacitance like effects. It can be both a pro and con in terms of noise though but I'm not sure under which circumstances that would be. Beyond that, it's easier since you don't have to route traces. Plus, you generally have a wider area for the power to travel across in ways that would be difficult to do with just normal traces (same sort of deal as for a ground plane).

[Shuriken]

As best as I can tell, it's to control impedance and has some capacitance like effects. It can be both a pro and con in terms of noise though but I'm not sure under which circumstances that would be. Beyond that, it's easier since you don't have to route traces. Plus, you generally have a wider area for the power to travel across in ways that would be difficult to do with just normal traces (same sort of deal as for a ground plane).

Well i did catch up on the easy part. If you have a look at the lm2675 datasheet and go to page 22. There is a pcb design you could almost make with just a knife and copper board.

My mb6582 psu design (which is a ref. design) shows something similar:

Edited September 27, 2011 by Shuriken

[m00dawg]

Is that a ground or power plane? Ground planes tend to be pretty common. Power planes seem to complement a ground plane (for the desired) impedance and capacitance effects). Although for a single layer board I guess it could go either way for which to use. I usually use ground planes almost all the time. This power plane stuff is pretty new to me though.

[Shuriken]

Is that a ground or power plane? Ground planes tend to be pretty common. Power planes seem to complement a ground plane (for the desired) impedance and capacitance effects). Although for a single layer board I guess it could go either way for which to use. I usually use ground planes almost all the time. This power plane stuff is pretty new to me though.

Well for my ref design you are right. It's a dual layer groundplane with vias. Which are not implemented yet on that image :rolleyes:

Edited September 27, 2011 by Shuriken

[m00dawg]

Aha gotcha :) For what it's worth to the conversation, a colleague from a local hardware group I'm apart of pointed this out. Has some good design tips for using power planes and other good tidbits to remember (I realized I had a some of my clock traces for my SRs on the top plane instead of my ground plane which isn't ideal as one example).

[Shuriken]

Aha gotcha :) For what it's worth to the conversation, a colleague from a local hardware group I'm apart of pointed this out. Has some good design tips for using power planes and other good tidbits to remember (I realized I had a some of my clock traces for my SRs on the top plane instead of my ground plane which isn't ideal as one example).

Good link. But i think it still applies to switching PSU. As they use high freq (250kHz+). So i can imagine you haven't seen any power planes. As i haven't seen any switching psu designs here :whistle:

[m00dawg]

True although if there are no downsides to using them for lower speed circuitry, I figured I might as well. It makes laying the board easier and it avoids wasting a bunch of copper to an etchant.