• State Resolved
  • Locked Locked
  • Replies 5 replies
  • Answers 1 answer
  • Subscribers 64 subscribers
  • Views 518 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

UCC2897A: UCC2897A FG mechanical ground connection

Red Yen
Expert 4360 points
Part Number: UCC2897A

Hi Support team 

There are  -48V/52A and +3.6V/10A output.

The +3.6V converter is the forward converter (UCC2897APWR) that step down from -48V converter.

 For the original circuit:

The secondary ground of +3.6V is connected to the mechanical ground (FG).

The output and ground of -48V converter are isolated from the mechanical ground (FG) è see picture1.

 

Picture1: Original circuit

Question: Do we have any concern if we connect the positvie 48V (Net 48VL) to the mechanical ground (FG)?

See below picture2.

 

Picture2:  We connect the positvie 48V (Net 48VL) to the mechanical ground (FG)

Here is the simplify the circuit from picture 2.

thanks a lot 

  • 0
    TI__Guru 73005 points

    Hi,

    If you connect GND of 3.6V and 48VX, then you break the isolation barrier. Your design is no longer an isolated design. If you are ok with this isolation/insulation break, there is another question, if that is a single end connection, it is ok. So please check anything else connected to GND of 3.6V to form a loop, and if so, then need to make additional analysis.

    So it is not ok for an isolated design and application. But for a non-isolation design, possible additional loops need to check.

    So in simple words, it is not ok.

  • 0
    TI__Mastermind 32775 points

    Hi Red,

    Seems ok but make sure to verify isolation with an ohmmeter and check to assure that the 48V output which is feeding the UCC2897A input, is completely referenced to the same mechanical GND.


    Regards,

    Steve M

  • 0 in reply to Steven Mappus1
    TI__Expert 4360 points

    Hi Hung and Steven, 

    thanks for your reply, 

    Refer to previous question (picture2) that my customer connect the positive 48V (Net 48VL) to the mechanical ground (FG)

    Is there any chance to have a current path between Net 48VL & the ground of 3V6_MCU?

  • 0 in reply to Red Yen
    TI__Guru 73005 points

    Hi,

    I think that is what the customer needs to find out based on their connections. The customer needs to find if the isolation barrier is still ok, and if there are additional paths between between 48VX and +3.6V_GND, and also what is the impedance between the two spots. 

  • 0 in reply to Hong Huang
    TI__Guru 73005 points

    One way to check this is to apply the required breakdown voltage between the primary and the secondary to see after this connection the required breakdown voltage and leakage current specs are still met, if the customer is not sure if the connection is ok or not. Basically this is a safety consideration, the customer needs to test by themselves to make sure it is ok or not ok per their safety specs.