Hello,
I was designing a charger circuit for my LIPO battery. I wanted to feed the power with a micro USB connector. Then I saw a shield label at the micro USB. My question is should I connect the shield to ground?
Thanks.
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GND on most computers is connected to earth.
A shield is connected to earth on one end of the cable.
Thanks for the answer,
Correct me if I am wrong. Most computers shield is connected to gnd. So I don't have to ground the shield again. Right?
Back at the computer that’s probably true, that’s where it should be done.
But, don’t guess check it with a DMM.
Thanks for the answer,
What happens if I connect shield to ground?
The shield connected to GND at both ends can result in loop current (60-50Hz hum) influencing the internal conductor signals. The shield does not do its shielding job of preventing EMI. Also it’s job to reduce the effects of static is compromised.
A shield is like a cage (faraday cage) to keep outside stuff outside 
.
Thanks for the answer,
In conclusion I am not going to connect shield to ground. Because, If I connect shield to ground it can cause EMI problems.
Some sources will directly ground them, some will put like a 100 ohm resistor in between. Some sources suggest leaving it floating.
It is not as if it makes a functional difference. Not that it protects anything from ESD in any meaningful way.
On the Leonardo it look like it's ... hm. A "soft ground" through resistor.
On the Micro it is a hard ground -- they literally go directly to the same flood fill.
The Due also have two hard grounds.
Thanks for the answer,
How do they choose which grounding type to use?
Circuit design?
pin 1 is VBUS and pin 5 is GND. If you want a "soft ground" you connect the case/shell to the GND pin via a resistor (100 ohm for instance)
and if you want a hard ground, you connect them together via copper wires/fill.
How do they decide between two? I don't know. As said, the difference is basically zero and it does not protect against ESD in any meaningful way, UNLESS you have a metallic chassis and you meticulously differentiate between signal/power ground and case ground. Like in a desktop computer, which, depend on the power supply, may not even have a "signal ground". The resistor will make it so in the event that the user (or whoever/whatever it is) that touch the case, the current (due to ESC) will be somewhat limited by that resistor as they rush toward ground (or come from ground, depend on the net charge).
In a ideal world, all "case" (or metal shells for everything that gets power from a power station) should be connected to safety ground and all signal pins should NOT be tied to safety ground. However, this means that all USB cables must carry the 5th connection called "shell" that would be the "safety ground", which is only present on "good" cables.
Which is the argument of leaving the USB "shield" floating (because it should be connected to a separate "safety ground"). This is so that under all circumstances (an internal fault, a person carrying around charge) any excess voltage/electrons/charge will find its way to safety ground before getting the way to the user/internal circuitry, thereby minimizing damage.
Does that matter? No. In fact in many cases (benchtop multimeter/oscilloscope, laptop power bricks) for instance the ground is often hard-grounded like I mentioned, for stability and other reasons.
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