The data sheet shows something like this, but they isolate an area of the bottom ground plane directly under the chip from all of the other large PS components on the top side... I am guessing this is to reduce the transfer of heat from the chip to the big caps and diodes. There is still a wide "tail" of copper on this area, so I guess that's effectively the heat sink.
I was mostly able to reproduce this, except I needed a bridge between those bottom copper areas to keep all my grounds connected. With the top components crammed so tightly together, there wasn't room for the ground pour to get in everywhere and still keep 10th isolation.
I do wonder if I'd be better off loosening up the layout a bit. Assembly is going to be fun... :-)
--- In Homebrew_PCBs@yahoogroups.com, "RDHeiliger" <rdheiliger@...> wrote:
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> Have done a number of boost and buck converters, down to .5mm. Done them all single sided. If you fiddle with the layout you can get the traces pretty short. Look at the data sheets, there is usually layout recommendation art work. The most important point is to make the grounds to the chip and caps a single point ground, usually need to run a wide trace under the chip to do this, and the heat sink will be ground as well, this allows you to add extra copper for heat sink on each end. Also keep the inductor as close as possible with very large traces/pads. The recommended heat sink area is for the maximum current for the device, if you are running less that that you can get by with a little less heat sink.
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> RD
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