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Sea Jay , 04-08-2025, 06:06 AM

I am working on a project that uses a GNSS receiver module in it. It will be used in some automotives and hence will be battery powered. Does anyone have any idea on how should the grounding be?

Can I just short the product chassis to the power ground and system ground. All together? Interfaces if any will be isolated. Can it be done so? Any Radiated and conducted emission care necessary? What care should be taken with layout for grounding and for cable harnessing of I/O connectors and for antenna connectors? I have a full metal enclosure with a heat sink for GNSS receiver module connected to the chassis.

Hoping to hear from y'all! Thanks in advance for your insights and any resources you can provide!

Sea Jay , 04-08-2025, 11:31 AM

@QDrives @Robert Feranec

In need of your expertise.

Robert Feranec , 04-08-2025, 11:50 AM

This may help: https://youtu.be/Hj-HVve1QC4

Sea Jay , 04-08-2025, 02:20 PM

Hey Robert, thanks for your response.

Went through the video. Interesting. Still need more help.

Can I just short the product chassis to the power ground and system ground. All together? Interfaces will be isolated. Can it be done so? How is it usually done for automotive, do you have anything to refer to? @QDrives @Robert Feranec

Sea Jay , 04-08-2025, 02:46 PM

Because I found this online

*The shield of the TNC antenna cable is connected to the chassis of the device, and on the GNSS receiver this shield is connected to the power return potential. Since that is the case, the whole enclosure is under the same potential. We recommend users to isolate the chassis from the power return potential if it is required in their application, as we have not had any problems related to chassis isolation in any application.

In addition, it is important to note that the main connector body connects to the cable shield when the cable is plugged into the device. The cable shield is separate from the power return potential and since the connectors are isolated from the body, the user can attach it to any potential using the shield of the cable.*

Can you help me understand this?

QDrives , 04-08-2025, 04:01 PM

A lot of questions and all in specific domains.
"Any Radiated and conducted emission care necessary?" -- Yes, automotive has EMC requirements. To my knowledge there are 5 levels. Standard is CISPR 25.
"Can I just short the product chassis to the power ground and system ground." -- There are many theories about it, both in favor and against making it all the same ground. I did see "shielded enclosure" as a 'chapter' in CISPR 25. However, I do not know if there are other automotive requirements to isolate chassis from power ground as is the case in maritime.

Sea Jay , 04-08-2025, 04:21 PM

Okay thanks @QDrives

Sea Jay , 04-08-2025, 04:22 PM

Any inputs on this?

QDrives , 04-08-2025, 06:57 PM

"*...as we have not had any problems related to chassis isolation in any application.*" -- And did they had problems when the chassis was not isolated?
But you should start with this "*...**if** it is required in their application*" and that I already mentioned/asked.

QDrives , 04-08-2025, 06:57 PM

Can you ask your customer for details / help?

PT , 04-09-2025, 11:43 AM

If your product is in a metal box, it will end probably end up being connected to chassis somewhere in the vehicle.

Like @QDrives said, CISPR25 covers automotive emissions generally. If you’re working with a large OEM, they usually have their own standards and tests based off CISPR25 you follow. You need to talk to your customer about their EMC requirements to make sure you follow anything specific they have.

For the power return, if your battery power comes from the LV vehicle battery then your power is single ended. If that’s the case, then you want to have a low Z connection between the 12V return and your chassis so any HF noise on the cables (from the vehicle or during automotive immunity testing) has a path to chassis.

You need a cohesive grounding strategy. If your project is big, and distributed across several boards connected by harnesses then it’s different vs only 1 board in a box.

Cable harness are probably going to be your biggest issue, since they penetrate any shielded enclosure. If you have control over how they are routed and bundled, you want separation between aggressive and sensitive signals as well as some between internal (doesn’t leave the enclosure) and external (exit the enclosure) cabling. General rules would be to NOT route cables nearby or over the top of active parts. Coupling happens in all 3 dimensions so be aware of where your aggressive signals are in relation to any cable.

I/O connecters you generally place on one side of the PCB. If you have a large Pcb and put connectors across it, then any noise that couples to the I/O forms a dipole structure. Another general rule is all unshielded I/O should be filtered. Any I/O subject to BCI or automotive transient testing will probably need extra filtering.

PT , 04-09-2025, 11:43 AM

Automotive EMC is a big world, you really need to talk to your customer and figure out what their requirements for an ESA (electronic sub assembly) are. Since you have a GNSS receiver, immunity could be a large part of testing

PT , 04-09-2025, 11:51 AM

As a very general rule, all your “grounds” will get connected together and isolation of noise between them can be achieved with separation.

In specific circumstances you can use a separate return and have a gap spanned by some passive component (usually a ferrite bead to tune the impedance profile you want) but this is the exception, not the rule. This strategy is only useful for low speed, external I/O lines that are coupling in a lot of noise

Sea Jay , 04-11-2025, 01:17 AM

@PT Thanks for your inputs.

I need some help in understanding and simulating possible ground loops here.

Sea Jay , 04-11-2025, 02:49 AM

Can you see any possible issues with these? #1 or #2, which seems better?

@PT @Robert Feranec @QDrives

QDrives , 04-11-2025, 07:05 PM

I think you first need to find out the customer has for requirements.

Sea Jay , 04-12-2025, 03:48 AM

@QDrives Did ask. Customer doesn't have any. So trying to go with the fundamentally best one.

QDrives , 04-12-2025, 03:36 PM

I usually tie everything together.

PT , 04-13-2025, 12:43 AM

Same, for the HV stuff I work on we need everything connected for isolation checks anyway.

For resources, check out Min Zhang and Todd Hubing. They both do a lot of automotive EMC work

Sea Jay , 04-13-2025, 04:45 PM

Thanks