| Electronics > Projects, Designs, and Technical Stuff |
| Layout review for buck-converter power supply |
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| thm_w:
I think you missed uploading the new photos? --- Quote from: LoveLaika on May 29, 2020, 04:29:42 pm ---There's so much empty space, so I'm trying to move some small stuff around in order to reduce the space, and therefore the cost of the PCB boards. --- End quote --- If its under 10x10cm then the cost will basically not change from the proto pcb places. --- Quote ---Regarding the feedback path, the issue I have right now is that it starts at one end of the inductor, PCSP, and it has to connect to pin 6 of the IC. The pin placements are rather difficult to route without putting the components closer. How would you recommend routing it from C13? I'd have to move it around, but right now, it's still hanging at the top left unless I re-orient the inductor. --- End quote --- I would route a ~6mil trace from C13 or C11 somewhere, back to the potentiometer. Its not critical, but something you may consider in the future: https://techweb.rohm.com/knowledge/dcdc/dcdc_pwm/dcdc_pwm03/4682 --- Quote ---Regarding C12, I can move it , but as long as it's connected properly, the sense resistor can just connect to C10 instead of C12, correct? The two caps are parallel, so as long as they are connected at the same node, I can put C12 across from C10 and move the components closer together to save space. --- End quote --- think so |
| LoveLaika:
Sorry about that. I thought I attached it. My bad. Here's the new layout. Hopefully it worked this time. To recap: --- Quote --- I tried to take into consideration what you said by first rethinking some placements. I saw on other buck converter modules that input to output was going from left to right. Following that flow, I've managed to move parts around which resulted in a smaller feedback loop as well as shortening the trace of the feedback pin. I had to make the trace to the input capacitors slightly longer with a via, but I used thick traces where I could to make up for that. I also added some square through holes, TP1 and TP2 as places to probe with my multimeter when adjusting the voltage to make my life easier. Hopefully, they shouldn't be an issue. --- End quote --- Why is it necessary to route from the capacitor instead of the inductor if they're at the same node? Is it because of filtering done by the capacitors? I used 100 mil traces for the inductor and capacitors, but with this new layout, it shouldn't be a problem. I was more worried about the feedback trace between the pot and the IC (Pin 6, that long bottom layer trace). Also, thanks for the link. I'll have a look at it and see what I can incorporate |
| LoveLaika:
Sorry, I'm an idiot. After reading the link you sent, I see why you said what you said. I'll definitely have to avoid the diode and inductor when routing. |
| thm_w:
--- Quote from: LoveLaika on May 29, 2020, 10:09:32 pm ---Sorry, I'm an idiot. After reading the link you sent, I see why you said what you said. I'll definitely have to avoid the diode and inductor when routing. --- End quote --- Its alright, was referring to this part: "The place for detecting the output voltage should be either across the terminals of the output capacitor, or past the output capacitor" Inductor is probably shielded so not sure if that would be much of an issue, as long as you don't go right under it. Depending on current you are outputting (chip says 3A capable), you may want a few thicker traces and a extra via on U2-pin 2. |
| LoveLaika:
I followed the guide layout from your link. If you don't mind again, what do you think of it now? As you suggested, I took the feedback from the capacitors instead of the inductor, and I went around the inductor on the bottom layer to the feedback pot RV2 which shortened the loop significantly. One thing that kind of worries me is the negative feedback loop. Following TI's app note about using the LM267x family for an inverting buck-boost converter, the output is connected to ground while the 'ground' is now the negative output. In terms of the feedback loop in my layout, RV1 connects to ground at one end. It feels kind of strange just connecting it to the ground plane like that, though I did try to add a trace between the output capacitors to it, and it avoids the inductor. If it makes any difference, I'm using one of these plug and play 5-V modules from MPS, the MEZD71201A-G at U5 on the far right. All things considering, since that source is just powering the op-amps, I didn't consider it to be as critical as the switching components, so I kind of haphazardly routed it. I figured the bypass caps will take care of the rest https://www.digikey.com/product-detail/en/monolithic-power-systems-inc/MEZD71201A-G/1589-1458-ND/6823821 |
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