Ground Planes with Power and Mixed Signals
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- Опубліковано 12 чер 2024
- How do you bring analog power into a board, then route to digital components? In this video, Tech Consultant Zach Peterson shows you how to create the stackup and ground planes for this mixed signal scenario.
0:00 Intro
0:41 The Mixed Signal Scenario
4:04 The Ground Planes
6:45 The Analog Section
8:43 Protective Earth
11:01 A Sample Schematic
For more Mixed Signal Design videos, click here: • Mixed Signal Design
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For more PCB Design for Beginners videos, click here: • PCB Design for Beginners
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That was really terrific. First one I’ve watched. Exactly the right mix of theory, design, and implementation advice. I’ve been intending to try Altium for a while. You’ve given me the push I needed. It’s the least I can do given the effort you gave put into this. Well done!
Glad you enjoyed it!
Thanks a lot for all your interest.
Man this is such a helpful topic. Awesome
the best speaker
Thanks a lot for all your beneficial videos, I have a question. when you define PGND, do you mean "Null" line of the power from outlet or ground of the AC/DC converter?
To be clear, the ground section Zach draws in minute 5:00 is protective earth, yes?
I'm making a controller board PCB where part of it is a dimmer controlled by an MCU. It takes AC mains, but there's no transformer. Do I still tie the protective earth to my AGND/DGND via a safety capacitor?
There are a few ways to do it, you could have neutral and power routed as traces and then have the earth as a copper island on the PCB. You could also have that copper region as neutral and the hot power line routed. The main thing you should understand is that protective earth lines are not meant to carry a return current. So if you are bridging the SGND and PGND regions with a safety cap, then the PGND is neutral and not protective earth.
Super, merci beaucoup.
Please, What is the value of the capacitor between the primary and secondary ground ?
The standard guideline is to use a cap that has a larger value than the leakage capacitance of the transformer. The idea is to have higher frequency noise propagate back to the power supply return, rather than radiating or passing to an exposed connector where it could pass through the user to ground, so it is up to you to determine what the lowest frequency in the noise spectrum is and size the capacitor accordingly to provide low impedance across that isolation gap. The capacitor is typically a Y-type capacitor (that's the most commonly recommended I have seen), but the DC leakage current across the cap can also be important as this could create an annoying ESD shock if the user touches any plugs or connectors exposed in the system. This might also cause your design to fail some higher-end EMC requirements, such as in medical equipment.
@@Zachariah-Peterson merci beaucoup
…would you generally connect secondary ground on the board to the enclosure along w/ PE via a plated hole?
Let’s say we have a meanwell internal switching supply module. The IEC jack ground goes to chassis along with the internal power supply modules PCB ground. Then this internal PSU feeds your board. The board has its own secondary/signal ground plane. Does this ground plane ever get connected to chassis ground through a plated through hole?
Secondary ground is the signal reference, and that could be floating with respect to the primary ground in an isolated system. So if you mate the primary side to PE at the input, and then also the secondary side to PE, you now have no isolation anymore. Better option is to use a capacitor between PRI and SEC GND regions near the transformer, make sure it's a large Y-type capacitor. There are some reasons to put a cap to GND on the secondary side, but these relate more to ESD particularly from connectors. I wrote a Signal Integrity Journal article on how this is done in Ethernet that goes into why you might do this, and in fact there are reference designs and app notes on industrial Ethernet that recommend the same (they just do it really bad in the PCB latyout). In general, if not worried about ESD on the secondary side, you should bridge to the primary with a cap as I described above and do not connect secondary direct to the chassis (PE net). This is because the chassis now carries return current and this is not recommended for safety reasons.
@@Zachariah-Peterson ok thanks. In our application looking at the actual SMPSU (Meanwell RTP-75c) it has an earth ground PTH on it w/ safety caps already there, so we will chassis ground this hole along w/ the PSU case, enclosure and ground pin from IEC jack.
Is it acceptable to run ground traces on the signal/pwr layer of a 4 layer PCB? My stack up is: signal/pwr, GND, GND, Signal/PWR. The reason I want to do this is because there is one section I want to still have power when I disconnect GND from the rest of the board.
Yes you can route GND traces on the same layer as the PWR/signal traces. I'm assuming you have the GND on the sig/PWR layer at the same potential as the GND on your inner layers? From reading your question, it looks like you want to have two differnet GND regions, but overlapping in the internal layers, so when one GND region is disconnected you are still powering up the other region with its own GND, is that correct? If this is the case then you can do it but be prepared for radiated noise through the edge of the board whenever those two ground regions have a potential difference between them.
@@Zachariah-Peterson Thanks for your response! So I have the two inner ground layers and the ground trace at the same potential. Basically what would happen is as soon as the rest of the board looses power, the two inner planes would be left floating (that’s if you loose ground). The circuit also monitors for loss of high side power (12v) in that case, the ground planes would be at the same potential as the trace GND. I’m not concerned about that because this is a safety device (used in formula SAE) that will not be operating that way under normal circumstances. My plan is to route that separate power section as close as possible to the connector to minimize loop area. At the end of the day, the 555 timer has to stay on when the rest of the board looses power so that that fault latches.
@@Zachariah-Peterson the inner two GNDs are connected together with vias.
I'm 92% sure the transformer was sideways. Shouldn't the primary and secondary be isolated?
if used as transformer - yes. but in this case it was used as common mode choke 🙂
Altium can you route signals on planes? Cadence / Allegro has no restrictions and allows this.
Technically yes you can, if you plan to route signals within a plane layer then you would just define every layer as a signal layer and use polygon pour to define planes. Then you could route inside the plane layer and the clearance rule will set spacing between the plane copper and the trace. If you wanted to you could also draw out rails in a plane layer, but that's kind of time consuming if you just want to route a trace.
Did my whole master's with Altium! Now that I'm graduating, I'm sad as I will lose the license and won't be able to use it for my personal projects.. You should do a free/cheap personal license!!
Salut Christophe, c'est aussi cher que ça ?
hello, Howto enroll the course? Should i download the altium program to start learning ?
Do you want to enroll in the Altium Education program? It is free to enroll, go to education.altium.com and sign up for free. If you have an educational institution email address, you can also get access to a student license. If you don't have an educational email, you can still follow along with the lessons using CircuitMaker, which is a free tool and it uses the same menus/commands and very similar interface as Altium Designer.
@@Zachariah-Peterson thank you, No I dont have an eductional institution.
Altium should have uploaded all this stuff in detail 10 years ago. Why it took them this long to do this?
Can you explain the mixed signals from my wife please?
LOL!