Hey, thanks for the feedback! Sorry if I was confusing in my descriptions. I've attached an image of my board (board) that I working with now. What I was describing was that I was going to run my components and power traces on the top (red). Then on the bottom, I would run my signal layers (solid blue). In the middle would be a ground plane (mesh blue). I have labled my signal ground and power ground polygons. My question was, should I connect the ground planes on the top layer using a trace from vias A to vias B, or should I just let the vias connect to the ground plane for each polygon and that would be their connection together (being tied to the same plane through the vias). Also, you can see the power ground polygon extends a good bit through the circuit so I was wondering if it's better to leave it how it is, or break it up to more localized areas (still connecting to the ground plane through vias).
I've never done a 4 layer board before and like you've said, 2 layer I'd think should be fine. I've done up to 1kW on a 2 layer board with no problems. I do think on those I did a better job of running signals with their respective ground planes beneath.
My problem right now is on the converter shown(board current), it runs fine at 2A. It's a buck converter from 15V to 10V. At 2A output the inductor gets fairly hot, but everything is stable and the output only has about 150mV ripple, peak to peak. As soon as I bump up to 2.5A, the converter duty cycle goes unstable. Now, the output ripple is still the same and the voltage is constant. If I turn off the load and then start it again, it will run fine for a little bit, then the Vds spikes at turn on and turn off begin to decrease and then then duty goes unconstant again. When it shuts down, it keeps the 2.5A at the load, but the voltage is 0.9V.
The other converter I'm having trouble with is a boost from 3.6V to 9V at 3A. It does ok at 1A out but it seems jittery (looking at Vds). If I start the supply voltage at 4.2V it pulls it down to 3.4V. If i adjust it back up and step up the load to 2A it might pull it down again, but if it happens to work, the supply voltage will jump back up to 4.2V plus the amount I had to ajust it to get it back there the first time. It seemed adding an RC snubber helped (couple of 603 components running over the mosfet body :roll
. I also added a larger electrolytic capacitor in parallel with the ceramic (on top of the IC) across Vin. I have been able to get it to work from time to time but only if i start at 4.2V and then once it's working, i can drop it to 3.6 and pulse the load just fine. When it drops the input voltage, the output current still meets what I want, but the voltage is no longer 9V but about 3.6V. I will say, the layout on this is pretty poor as well and could be a good bit of my problem.
My power supply is capable of delivering the full load power. I'm using about 1 foot of stranded 14 guage wire twisted together. Only these two converters are populated at the moment and only one works at a time, so there shouldn't be any noise injected from one to the other.