• State Resolved
  • Locked Locked
  • Replies 3 replies
  • Answers 1 answer
  • Subscribers 62 subscribers
  • Views 150 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.

Original question:

LM5155: Connecting CS and COMP to PGND

LM5155: PCB layout grounding

Bob Zwicker
Prodigy 210 points
Part Number: LM5155

Related to the earlier post regarding LM5155 grounding: I see the same issue in LM5155 datasheet Figure 51.  This shows a recommended layout.  Because the Rs current flows into PGND it seems reasonable that Cf would be connected to PGND.

 

But I am surprised that Ccomp is connected to PGND and not AGND.  Rfbb is grounded to AGND so I think the E/A is referenced to AGND.

 

Should Ccomp ideally be connected to AGND?  I could wrap compensation components around from pin 6 to pin 7.

  • 0
    TI__Guru 65470 points

    Hello Bob,

    In both EVMs, the compensation components are connected to PGND. Please give me some days to clarify why the connection is done this way.

  • 0 in reply to Brigitte
    TI__Guru 65470 points

    Hello Bob,

    The functional block diagram on page 11 of the LM5155 datasheet shows that the CS input (CS2) is directly going to the comparator input to make sure that the same noise is coupled into both inputs of the comparator, the compensation components need to be connected to the same GND, in this case PGND.

  • 0 in reply to Brigitte
    Prodigy 210 points

    Hi, Brigitte

    Yes I see that.  It makes sense and leads me to wonder whether some other current mode boost controllers (which I have used) should also be done that way.  I guess the difference is likely to be subtle in many or most cases.

    Thank you very much.