| ??? 07/12/06 18:51 Read: times |
#120117 - thanks! Responding to: ???'s previous message |
wow, thanks for those answers Kai. Really helped clear up a couple questions I had
Kai Klaas said:
Take care, David, as Steve already mentioned, your TVS must withstand up to 100A, which is much higher than the peak current of human body model ESDs!! Eventually you must put some TVS in parallel or choose a higher rated variant. Ok, that's what I thought after Steve posted that number. I'll just find a higher rated part. Probably easier that way. Kai Klaas said:
All the TVS must be connected from each wire to chassis ground of your enclosure, right where the wires enter or leave the chassis! So, either you spend the TVS an extra board or you prepare a certain reserved area on your 4-layer board for the TVS parts only. ... Ok, I was planning to do essentially that. I was going to pay special attention to make sure I don't have errant currents running willy-nilly across the board. Kai Klaas said:
Connect the ground of 4-layer board to the enclosure where all the TVS are connected to. But choose a quiet location for it. Connect signal ground of your 4-layer board to chassis ground at only one point. Otherwise the ESD currents can again partially flow across your 4-layer board. what do mean by 'quiet' here? I'm planning on connecting the 'chassis' ground plane on the PCB to the enclosure, then to the truck frame (ground). Should I then connect the internal signal ground plane of the PCB to the enclosure at a different location, or at this same point? I'd imagine I want the signal ground connected (at one point only) to the Chassis ground, right where the ground wire goes to the enclosure. Kai Klaas said:
How the ground lines are treated depends a bit on your application. Is your device a stand alone thingy? Or is it mounted in a second, bigger enclosure, as a module? I believe it will be stand alone, plugging inbetween the vehicle (big rig truck) and another SBC computer product. My system is actually just a stopgap product while they try to convince the other company to add my thingys functionality to theirs. Kai Klaas said:
It's easy to design an ESD robust device: Just think about how the ESD currents are flowing (mostly on a path to protection earth) and how these currents can be prevented from running over your 4-layer board. No ESD current must ever flow across your 4-layer board!!! Not even partially!!! Yea, I figured it couldn't be too hard to do, but at the same time, easy to mess up. This is the first time I've had to design a circuit this robust against ESD; although I'm sure it won't be the last. Sometimes getting a few basic questions answered makes all the difference! Thanks again, -Dave (learning new stuff every day :) |
