-1

I am trying to implement Renesas IC, and seeying their design I have found something that I don't understand. I have read something about GNDs and USB connectors, and some manufactures recommend put the usb shield to gnd and other don't.

On this design there are two gnd lines: GND_Earth joins all USB shields, and normal GND. What is the different between these two gnds?

EDIT: I add schematic.

GND net.

GND_Earth net.

Schematic

Juanma
  • 360
  • 1
  • 16
  • Can you post a schematic how the GND_Earth connects to the system? Where else it is connected to except for the USB connector metal shields? – Justme Oct 29 '21 at 11:16
  • @Justme done. Is this a analog ground? – Juanma Oct 29 '21 at 11:27
  • What you're trying to with cable shields (like on a USB connector), is to shunt any noise that's coupled onto the shield to chassis, or earth (I hate to use that term) ground. You do not want that noise to get onto and contaminate the signal return (signal ground) on your board. Those zero ohm resistors R43-R46 are there so that the connection between chassis (earth) and signal return can be removed without cutting traces or re-spining your PWB. – SteveSh Oct 29 '21 at 11:33
  • @SteveSh But I don't understand what is the 0 ohm resistor function, Keep two different and separated nets or to choose if you want join both nets if you want? The noise don't pass through 0 ohm resistor? – Juanma Oct 29 '21 at 11:48
  • Solved on this thread: https://electronics.stackexchange.com/questions/137943/why-is-this-resistor-connected-between-connector-shield-and-ground – Juanma Oct 29 '21 at 11:54
  • 2
    Does this answer your question? [Why is this resistor connected between connector shield and ground?](https://electronics.stackexchange.com/questions/137943/why-is-this-resistor-connected-between-connector-shield-and-ground) – Justme Oct 29 '21 at 12:16
  • Sorry but I disagree. The linked answer doesn't answer this question: *What is the different between these two gnds?* - to do that question justice is to examine and discuss what surge events occur on the USB cable shield and decide whether you can adequately connect shield to local ground instead of enclosure chassis. – Andy aka Oct 29 '21 at 12:19
  • @Andyaka mmmm, the result of my question and the thread is more or less the same. I didn't see the difference between GND_Earth and GND but know I understand that there are two different nets with 0 ohm jumper that can be replaced by capacitors or resistors, or removed. Other different question is which case is better, doesn't it? – Juanma Oct 29 '21 at 12:40
  • 1
    @Juanma - In general, the purpose of a zero ohm resistor is to allow you to break a connection by removing a part instead of cutting a track. Isolating grounds (return nets) is one use. Another, that our power supply team uses, it to allow you to break the feedback path around a power supply so that the open loop response can be measured. – SteveSh Oct 29 '21 at 12:40

1 Answers1

0

GND is the place where you put the black crocodile clip of your multimeter.

EARTH is the place where, for safety reasons, you are supposed to connect the yellow-green cable of your house.

enter image description here

If in your board there are no places, with respect to EARTH, where the voltage exceeds 60 VDC or 43 Vpkpk AC than you can safely not connect the yellow-green cable to your board.

In some circuits, for Electromagnetic compatibility reasons, even though safety is not involved, engineers connect the metallic shield of the product/board to EARTH

Enrico Migliore
  • 4,161
  • 1
  • 9
  • 12