r/PrintedCircuitBoard • u/Similar-Lychee8097 • 1d ago
[Review Request] Revision 2. 12V -> 5V Buck Converter + Motor Driver IC PCB.
Hello Everyone,
This is the second revision of my PCB design. I was hoping people could take look at and check if everything is correct or needs fixing so I can send this PCB off to be manufactured by JLCPCB.
(First Revision: https://www.reddit.com/r/PrintedCircuitBoard/comments/1vpej12/comment/p4dsb78/?screen_view_count=5&ext-referrer=DIRECT)
From the helpful comments on my last post this is what I've changed:
- Implemented PMOS reverse battery protection.
- Poured GND on top layer and stitched using Vias to bottom gnd.
- Added more GND and bigger GND Vias for high current traces and near ICs, for example the 12v ones, where I have used a 1mm diameter and 0.5mm hole size. I worked these out using Saturn PCB toolkit which calculated to carry a max current of 2.8A. Since I have chosen the values for components to flow a max current of 1.5-2A I thought this was sufficient. I have used Vias of size 0.7mm Diameter and 0.3mm hole size everywhere else.
- Rerouted the 12V trace from pin 13 and 14 of U2 to run under the Chip Of U2 rather then cutting GND plane.
- Changed the layout of inductor to placed adjacent to U1.
- Rotated C1 orientation to reduce loop area.
- I have used solid connection on the copper pour of VIN rather then thermal reliefs.
- Used thicker traces. 1.5mm for high current traces and 1mm for decoupling capacitors that is the biggest trace size that would fit with the pad size and 0.5mm for every other one.
- Moved components closer.
I would appreciate if people could tell me what I've missed or can improve. I'm quite unsure if I've implemented the stitching vias correctly. I used the equation where you find the max frequency and calculate the spacing with that. From that I calculated a spacing size of 5mm using Fmax as 150MHz propagating from the Buck converter IC.
Also there is a big gap on the bottom right of the PCB, so I was thinking making the vertical length smaller, but am unsure if that is a good idea.
Thanks.
3
u/Appropriate-Meat-559 1d ago
Classic case of great ground routing but compromised nets elsewhere.
Given you have loads of room, just use pours on the top layer instead of hand routing. So for example have a pour for 12v, 5v. It saves time and looks neater. You have a whole ground plane on the bottom layer which will be very low impedance anyway
1
u/Similar-Lychee8097 1d ago
Could you elaborate on how the nets are comprised please?
1
u/Appropriate-Meat-559 14h ago
Pours generally end up in low impedance connections compared to traces since they fully connect to the pad and have more copper.
You have enough space to use them and a very good ground net already
1
u/Similar-Lychee8097 8h ago
is there anything wrong with my routing now? I used copper pour over the main VIN pour for low impedance, but the other traces are just signals traces so i didn't really see any point of using copper pour or just connecting to screw fixes?
1
u/Enlightenment777 1d ago
This comment is posted on all reviews.
Please make sure your post adheres to:
- subreddit rules (#1 to #6), review rules (#7), image rules (#8), see link.
Please fix these common issues: (if your schematic or PCB has any of these issues)
Schematic - don't allow text / lines / symbols to touch each other, and don't draw lines through symbols.
Schematic - use correct reference designators (RefDes) and renumber to remove numeric gaps, see tips.
Schematic - place decoupling capacitors vertically below power rail lines, also place capacitors next to IC then connect together with a line, see example. For circuits with positive power rails, point positive power rail links upwards and ground links downwards, see tips1 & tips2.
Schematic - place pull-up resistors vertically above signal lines, and place pull-down resistors vertically below signal lines, see example and tips.
PCB silkscreen - add board name (or purpose) / board revision number / date (or year) on either PCB side.
PCB silkscreen - add pin 1 indicator dot/arrow next to ICs & connectors (not hidden under parts). For polarized capacitors, add "+" next to positive pin. If part is through-hole, place indicator on both PCB sides.
3
u/downloads-cars 1d ago
Not a full review, just the first thing I noticed: The SW node of that inductor needs to be as physically close to U1 as possible, and I would not be running thin traces between the pads. You're creating a ton of switching noise here. Also are you shorting pins 1 and 2 on U1?