Stepper motor driver PCB design grounding - Page 1
Forum section: electronics / projects

author: tomshirvo
author_rank: Regular Contributor
timestamp: March 30, 2017, 11:10:00 pm
content: Good morning all,I am designing a PCB for a stepper motor driver and I need some feedback on how I am grounding everything.I have put all the motor driving electronics including mosfets on the top half of the board. The bottom half has all of the other digital electronics.I have flood filled the two halves but kept them separate from each other right up until the power connector that will have 4 12v batteries connected in series to produce 48v.I built most of this on a breadboard to test it out and I have so much noise on my encoder that it just wouldn't work. I think the reason for that was because of all the lovely jumper wire antenna and not really having a good star grounding point due to the jerry rigging of the setup. I have added RC noise filtering to all the encoder lines and made sure the encoder connects to the board at the opposite end of the stepper driver stuff.My question is... is what I have done with the ground planes with having them separate up until the power connector a good way to stop noise?Will having the board flood filled with GND stop EMI getting to any of my other digital electronics?

author: tomshirvo
author_rank: Regular Contributor
timestamp: March 31, 2017, 12:46:30 am
content: Hi Evb149, thanks for the time.I have attached another image showing the different fills. All other fills that aren't stated are GND.A) So it is a double sided board with ground on both sides apart from the +48v fill going to the mosfets.B) Those traces crossing the split do need to have sharp edges as they are used to control the mosfets with PWM

author: BrianHG
author_rank: Super Contributor
timestamp: March 31, 2017, 01:06:20 am
content: I don't get it, are your gate drivers on a separate ground plane compared to the mosfets?

author: tomshirvo
author_rank: Regular Contributor
timestamp: March 31, 2017, 01:12:21 am
content: BrianHG, everything has the same GND. The gate driver is on the same GND fill as the mosfets but everything else on the board is on a separate GND plane that is connected directly at the Power connector. I did this to try and create a star GND between the high power side and the low power digital electronicsI guess I am trying to make it as if the stepper motor driver part was on a separate board to the controlling electronics but they are still on the same board. I have done this because of noise issues from the 48v 5A stepper motor circuit.Please let loose with your comments, I'm more then happy to be put in line about my shitty layout if that's the case.So I just did another layout show in the picture but I am now thinking this is worse. The gate drivers should have a good GND return path for the mosfets?

author: BrianHG
author_rank: Super Contributor
timestamp: March 31, 2017, 01:28:15 am
content: I could better visualize your layout if you provided 2 screenshots, one with just the top layer and one with just the bottom enabled.I'm assuming the GND is the fill on the bottom of the PCB...Having net names on the PADs enabled will also help...

author: tomshirvo
author_rank: Regular Contributor
timestamp: March 31, 2017, 01:40:20 am
content: So here is the two layers, I am unable to put the net names as my version of eagle doesn't have that option.

author: tomshirvo
author_rank: Regular Contributor
timestamp: March 31, 2017, 01:56:16 am
content: So after skimming over those links, it really sounds like I SHOULDN'T use split ground plane. All of my components are digital electronics apart from the current sensor which is analog but outputs an i2c signal.The current flowing to and from the stepper motor has a clear direct path to the power connector that is clear from any of my other digital electronics.So is my conclusion of not splitting the GND plane seem like the way to go and my thoughts of splitting it really wouldn't have done anything but make it worse.

author: tomshirvo
author_rank: Regular Contributor
timestamp: March 31, 2017, 03:11:59 am
content: Thanks for all your help.The community on this forum is amazing. The world couldn't be that bad if it is filled with people like all of you that are willing to help noobs like me.Thanks again

author: BrianHG
author_rank: Super Contributor
timestamp: March 31, 2017, 03:16:01 am
content: The comments above are correct. With this PCB, if you must use a 2 layer PCB, reserve the bottom for a complete GND pour with only occasional tracks where you must. Keep them short so you can avoid the example issue I illustrated in my attached photo of your PCB. Your PCB isn't too complex and you should be able to really clean things up to make a successful 2 layer PCB, placing many more traces on the top with a little effort in orientation & layout.