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UCC34141-Q1: Grounding scheme doubt

BOOM
Prodigy 155 points
Part Number: UCC34141-Q1


Tool/software:

I am using UCC34141-Q1 for isolated DC/DC conversion in my automotive product and need some help with the grounding scheme. Sharing a snip below. Is shorting the transceiver isolated ground (GND_ISO) and power ground (GND_P) leading to any issues? Is the isolation compromised?

  • 0
    TI__Mastermind 33115 points

    Shorting GND_P to GND_ISO means that the VIN return (GND_P) is now connected to the GND_ISO but GND_D should still be isolated from GND_ISO+GND_P. Once this is built in hardware be sure to check the board for isolation/continuity between grounds to be sure it is as you expect.

    Steve

  • 0 in reply to Steven Mappus1
    Prodigy 155 points

    Should isolated ground of interfaces be isolated from any such grounds (GND_P here) or is it fine to connect it? Any inputs on that please?

    How are these affected?

    Yes GND_D is isolated.

  • 0 in reply to BOOM
    TI__Mastermind 33115 points

    You have to define the grounding isolation in your system and then apply the appropriate isolation level components, PCB separation, etc. What you've described so far is that GND_D and GND_ISO are isolated but I'm not understanding if GND_P and GND_D require isolation? From your diagram, it seems GND_P and GND_D are both on the LV side GND and GND_ISO is HV GND - correct? If this is true, then why use an isolated module (UCC34141-Q1) to isolate GND_P and GND_D? 

    Steve

  • 0 in reply to Steven Mappus1
    Prodigy 155 points

    It is for isolating the power input, it is a specified requirement from the customer.

    A. Also, if I am using a GNSS receiver in this product and the antenna connector is mounted on the metal chassis, GND_CHASSIS and GND_D will then be shorted there. How is it to be done in such cases?

    B. If I short GND_ISO to GND_P, is it violating the isolated ground requirements of transceivers and possibly giving rise to more issues? 

    C. Automotive vehicle chassis has the battery ground on it. Then if the product is mounted, GND_CHASSIS and GND_P will be shorted. How about it then?

    Any inputs are appreciated. Thanks.

  • 0 in reply to BOOM
    TI__Genius 11350 points

    Hi Boom,

    I apologize for the delay as Steve is out of office until Monday. I would like to wait for him to return to continue this thread if that is OK.

    Regards,

    Ray

  • 0 in reply to Ray DiCecco
    Prodigy 155 points

    Okay 

    Grateful for any inputs.

  • 0 in reply to BOOM
    TI__Mastermind 33115 points

    The grounding scheme you choose is according to your system requirements - I don't really understand the question you are asking but I'll offer the below comments. 

    A. Also, if I am using a GNSS receiver in this product and the antenna connector is mounted on the metal chassis, GND_CHASSIS and GND_D will then be shorted there. How is it to be done in such cases?

    • I'm not familiar with GNSS receiver system grounding requirements

    B. If I short GND_ISO to GND_P, is it violating the isolated ground requirements of transceivers and possibly giving rise to more issues? 

    • Your block diagram shows three isolated grounds, GND_P (input voltage is referenced to GND_P), GND_D and GND_ISO. If you short GND_ISO to GND_P you only have GND_D as an isolated ground "island" but as mentioned above, I'm not familiar with your system grounding requirements and why there are three isolated ground references?

    C. Automotive vehicle chassis has the battery ground on it. Then if the product is mounted, GND_CHASSIS and GND_P will be shorted. How about it then?

    • I am familiar with automotive grounding and as you state, vehicle chassis and battery ground are shorted. In an EV application there are chassis mounted components, such as the traction inverter/motor which make up the power train. Inside the metal inverter case are circuit card assemblies (CCAs) with IC components that can be referenced to the LV and HV sides of the isolation barrier. The CCA can sometimes be floating but it is more common to connect the VIN- to the metal inverter case which is then connected to the car chassis. Whether the CCA is grounded to VIN- or floating, maintaining isolation between the LV and HV regions is critical.

    Steve