Mp8638: GND, PGND, AGND?

DC-DC Power Converters
1

Hello! I have been reading MP8638 datasheet and it is really unclear on the grounding pins:

  • page 3 shows pin 2 as PGND, pins 4/5/6/7 as GND,
  • page 4 lists pins 2/4/5/6/7 as PGND and does not mention GND at all, but mentions AGND in the description of pin 3,
  • functional diagram on page 11 show that distinct pins AGND and PGND exist, but does not specify which ones they are,
  • page 13 mentions AGND again,
  • page 19 has a pointer to “AGND to PGND Kelvin connection”, without saying where AGND is.

Overall it is rather confusing and in the end I have no idea whether pin 2 should be treated any different than pin 4/5/6/7, nor what is AGND and GND. Is AGND the other grounding (i.e. everything else’s than MP8638? What is meant by “Kelvin Connection” here?

Can anyone please share some light on this? Thanks!

2

Hello, welcome to the MPS Forums!

Definitely some good questions regarding the differences between AGND and PGND for this IC. I will check in with our PLs and get back to you on this request.

However, to address your other question here, a Kelvin connection refers to a 4-wire connection method for highly accurate measurements of voltage or resistance. The idea here is to minimize the effects of lead resistance and contact resistance. I suppose this is only visually implemented in the layout. Were you wondering about more details on an implementation here?

3

Just received feedback from the PLs on this question:

“Pin 4 GND is designed to be the AGND while the other GND pins are PGND. To facilitate the layout, Pin 4 can be connected to Pins 5, 6, and 7 directly.”

Hope this clarifies things. Let me know if there are any additional questions. I will push this clarification to represented in the documentation of this IC.

Best,
Krishan

4

Hi Krishan,

Thank you for clarification. As for the Kelvin connection, it just seemed out of place in this context.

Thanks again!

5

Understood on the comment about the Kelvin connection since it was just mentioned once.

But in the context of the PCB Layout, this is just a comment with the intent of the importance of making sure the voltage offset and noise between these two GND connections are minimized.

6

Since this resolves the differences between AGND and PGND, I will now close this post. If you have any additional questions, please reference this post in a new inquiry.

Best,
Krishan