Proper grounding of different GNDs

Thread Starter

AlexX 52

Joined Mar 15, 2018
14
I'm almost done with my first pcb design. The last thing I have to do is setting up a ground plane. Since I have no experience with ground planes at all, I wanted to ask for advice concerning the following situation:

My circuit consists of the following components: A USB-C connector, an IC (more specifically the BQ25890) and a few discrete components. At first I connected all the GNDs to one big plane on the top layer until I realized TI suggested connecting analog and power ground together. This topic seems to be quite controversial as I couldn't find a clear answer on the internet.

So my questions are:
  1. What is the preferred way to connect different GNDs?
  2. Should I put GND-planes everywhere on top and bottom layers?
  3. Let's say I add some more ICs. How do I know to which ground it needs to be connected to?
  4. Bonus question: How do I connect the USB-C shield?
I appreciate any answer answering even only one of them. Thanks in advance.
 

Picbuster

Joined Dec 2, 2013
1,022
Normally you start with identifying the power and ground currents.
Then you make sure that these are routed correctly in relation to inputs and currents flying via that ground plane.
A ground plane have length and width it could act as an antennae ( reflector or director) for certain frequencies.
Remember that a ground plane is a resistor a current will lead to a voltage over that part of the gnd.
That effect could have an effect on the inputs and outputs of a connected chip.
Usb shield is connected to protective ground avoiding ground loops with connected device(s).

Picbuster
 

dendad

Joined Feb 20, 2016
3,602
Do your best to seperate the power ground from the analog ground.Then connect them at only one place. That could be the agnd of the processor. Idealy, you want to have no current flowing in the analog ground so the signal you are trying to measure is not corrupted.
On my boards, the ground plane has slots in it to seperate the current paths.
 

MaxHeadRoom

Joined Jul 18, 2013
21,447
Unfortunately Ground is a rather indefinite as it includes Earth ground, and in many cases where transmission is involved, and/or remote connections, a star point earth ground is used to connect all system commons with the service earth conductor.
Max.
 
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