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| Layout review for buck-converter power supply |
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| thm_w:
Looks good to me. The feedback trace doesn't have to be thick, as it carries little current, but if its thin or thick it doesn't change anything. Yeah with the planes you can sometimes have a cutout to pass a trace through, but with such a large plane and not too high density, wouldn't worry much. |
| LoveLaika:
Thanks for your reply. I had to redo some parts due to my rookie mistake of incorrectly using the wrong op-amp pin out, but that didn't change my overall design. Thanks for your guidelines. They've helped a lot. What you said about cutouts, that brought to mind another question I had. I saw some other posts that people did with their power supplies as well as TI's LM2673 datasheet that for the top layer, I guess they kept it a signal plane and had their bottom plane to be ground. This appears to lead to 'segmented' copper areas on the top plane. They also kept some copper from going under components, so we have 'islands' of copper dedicated to one trace. Why is this done, and is it recommended I do the same? I've mentioned before that both top and bottom planes are ground planes, but if I put some no fill zones, perhaps it may help? For example, thinking of the negative regulator feedback, if I put no-fill zones at the output capacitor grounds and the two pins on RV1 (trimmer) connected to ground, I can put a trace that routes from the ground of the capacitors to RV1 so there will be a big trace that connects them together (and some small traces that connect them to the ground plane on the bottom side). https://electronics.stackexchange.com/questions/493621/pcb-critique-soft-start-power-distribution-from-24v-battery |
| thm_w:
I think they didn't purposefully remove ground fill, they just used those wide islands as high current transfer paths and then didn't bother with a ground fill. Its more work to set up another plane, and make sure they pour in the correct order. In some cases you might want to avoid ground for HF circuitry. https://electronics.stackexchange.com/questions/39239/when-to-use-ground-plane-cutouts Thermal reasons for soldering as well (or can adjust plane connect rules). What you suggest is a good idea, whether it makes a significant difference for the extra layout work, not sure. The hard part is when you move stuff around, you'll often have to redefine these cutouts. |
| LoveLaika:
Thanks for your reply. I kind of searched around a bit myself, and I found some links that highlighted the issue. It seems that the old practice was to not put copper fills in order to reduce EMI, but since my inductors are shielded, who knows how much it will help. https://e2e.ti.com/support/power-management/f/196/t/538740?-DC-DC-Converter-Ground-plane-cut-below-power-inductor http://rohmfs.rohm.com/en/products/databook/applinote/ic/power/switching_regulator/converter_pcb_layout_appli-e.pdf I went ahead and just decided to cut out the top copper pours under the inductor (and the catch diode). I thought that it would be safer to follow this practice than to not follow it. The rest of the circuit seems fine to leave alone (famous last words). I still kept the bottom layer ground pour untouched, so we'll see how that goes. Well, I submitted my board and ordered my parts. Here's hoping for the best once everything arrives. Funny how after I submitted my board that I realized I forgot to add more silkscreen. Not a dealbreaker, but it would've been real nice to have instructions on the back of the board. |
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