Anyone want to critique my board layout? - Page 1
Forum section: electronics / projects

author: viperidae
author_rank: Frequent Contributor
timestamp: September 15, 2020, 10:37:08 am
content: I've done a few layouts in the last few years, this one I want to do "right".It's effectively a CAN-Bus controlled high-side driver, with the intention of being programmed as a car trailer plug module.The last two cars I had towbars installed on, the garages did a pretty crap wiring job, with the trailer plug just spliced into the tail light circuits.My latest carwillrequire a module and they're a few hundred bucks, so I figured I may as well make my own... and if I'm going to make one, I may as well do it properly.I've found some reasonably priced high current automotive connectors and some high-side drivers designed for automotive lighting. It's reasonable to expect the brake light circuit on a trailer to be up to 50W of incandescent bulbs.The quad channel driver is designed for 27W bulbs per channel and the dual channel is designed for 2x27W per channel.I plan on using an STM32F303K8 and I've tried to only use pins available on a Nucleo-32.I probably won't be populating some of the components:- I don't really need the RTC xtal, it might be handy to calibrate the internal RC. CAN is only 100k, so RC should be OK on its own.- Don't need headers for UART- Don't need LED's for a "black box" buried behind a panel in the boot but handy for developmentThe split in the flood fill is a +12V plane for the driver heat sinking and ground on the MCU side.Sorry the schematic is a bit of a mess...Ps: any better way to share board designs on here? I'm using KiCAD and there's a bunch of custom parts from a bunch of random part librariesPps:I'm planning on sending this off to JLCPCBMaybe not, they want $20 to ship my $2 PCB order.

author: phil from seattle
author_rank: Super Contributor
timestamp: September 15, 2020, 05:43:17 pm
content: Quote from: viperidae on September 15, 2020, 10:37:08 amThat is par for the course. Though, can you find an outfit that has lower shipping costs (that doesn't take a month) or don't have much higher board fees? My guess is you will wind up paying about the same or more no matter what. In the US we have OSHPark which takes just a bit longer but free shipping. The cost of a 50mmx50mm board is about the same ($5/insq) so I use it a lot for little boards that I will populate myself. Sometimes I make small test boards for parts I'm not familiar with prior to ordering the full boards.You should determine all-in costs. I would consider having them mount and solder the SMT parts as well. I've mostly stopped building up my own given the relatively low cost of their assembly service and dirt cheap components cost. Plus, I don't have to place a separate order for the parts (including shipping and handling). shipping cost remains the same. You'd need to engineer the board for their library but the parts cost, even with the extra charges for "extended parts", tend to cheaper than ordering from western distis.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: September 15, 2020, 06:02:07 pm
content: Don't split ground.If you need polarity protection, put it on +12V.Needs transient protection as well, say SMAJ18A from GND to +12V.Needs a bit more ground stitching around the middle: observe the negative space around traces, see how they cut slots into the ground pour. Avoid traces in the same place top and bottom, so ground can be stitched over/under them. Minimize area of trace crossings, and stitch around them.The high density vias around power components aren't necessary. I'd use... probably 4 x 20 mil i.d. vias in those locations? And probably 6-8 x 12 mil vias for the power pads on the switches, with a few 20 mil vias outside the pad.If you must split ground, at least use common mode filters between ground domains, or preferably level translation, or even full isolators. Consider if voltage appears across the split (which is the point of doing it, after all, you're intentionally inviting a potential difference): logic levels to devices on one side or the other will be violated, or even ratings exceeded if the voltage is enough.Tim

author: viperidae
author_rank: Frequent Contributor
timestamp: September 16, 2020, 07:20:18 am
content: Those aren't split grounds, the power devices have their pad connected to +12V.One half is gnd pour, the other is +12V.The reverse protection diode between gnd and batt- is from the datasheet. My trailer module is the least of my concerns if the car battery is connected backwards so I'll probably not use it.All the vias around the power devices are for both heat and current.

author: viperidae
author_rank: Frequent Contributor
timestamp: September 17, 2020, 01:27:42 am
content: Seeedstudio have some cheaper shipping...$5 for boards and $10 shipping.It'll take a bit longer but I don't need DHL express.