Timeline for USB shielding, device or host side?
Current License: CC BY-SA 4.0
12 events
| when toggle format | what | by | license | comment | |
|---|---|---|---|---|---|
| Apr 7, 2023 at 8:16 | answer | added | 比尔盖子 | timeline score: 11 | |
| Apr 7, 2023 at 7:38 | answer | added | Justme | timeline score: 3 | |
| Apr 7, 2023 at 7:23 | comment | added | Justme | @TimWilliams Coax is a completely different situation and unrelated to shielding USB and other shielded differential pairs, and it may be even more complex subject where to bolt a coax connector ground to handle return currents, which are mostly high frequency anyway if coax needs to be used. | |
| Apr 7, 2023 at 7:09 | comment | added | Tim Williams | Should coax just never be used, then? It's impossible as far as I can tell to use it for DC-coupled signals without also passing DC current through the shield. | |
| Apr 7, 2023 at 6:56 | comment | added | Justme | @TimWilliams Shield must not have DC currents; for that there is the common ground wire, for return currents and for common ground reference between devices. I never claimed anything else what you talk about wider common mode range. I simply wanted to point out that blindly saying that USB must always have cable shield connected to ground at both ends is incorrect. The ground return wire obviously needs to be connected between devices. And really, the discussion when to connect shield to ground or how to connect it even indirectly would be endless as it is case specific. | |
| Apr 7, 2023 at 6:40 | comment | added | Tim Williams | @Justme Which return currents, specifically? (signal? power?) And by "good system" you mean USB specifically, or more general? USB signals themselves are common ground; there is absolutely no avoiding a ground loop, short of isolating one or both sides entirely; the question is GND wire, or shield. I've never seen a USB transceiver that claimed wider than 0...VCC common mode range (unlike RS-485 for example, which is made to operate over a wider range). Would you like to move this to a chat? | |
| Apr 7, 2023 at 6:19 | comment | added | Justme | @TimWilliams Most often a good system never has return currents in the shield. Connecting the shield to ground on both ends and having a ground wire will result in currents in the shield and is already a ground loop. Just google USB appnotes how to connect the shield for example. But USB is a difficult case as e.g. a mobile phone can be both a host and a device so the best practice will be case specific. For other buses, they simply define that shield must be connected on one end only. For example most RS-485 based industrial buses. | |
| Apr 7, 2023 at 5:41 | comment | added | Tim Williams | @Justme Could you provide some examples where this is the case? I have never seen a system where ground and shield are not within millivolts or tied directly. | |
| Apr 7, 2023 at 4:34 | comment | added | Justme | @TimWilliams Where to connect the shield is never that easy. On many situations the shield must not be connected to ground on both ends, as it depends on the situation you are in. | |
| Apr 7, 2023 at 1:01 | history | edited | ocrdu | CC BY-SA 4.0 |
added 6 characters in body; edited tags; edited title
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| Apr 6, 2023 at 22:47 | comment | added | Tim Williams | The shield must be grounded at both ends, as close as possible to circuit ground, while surrounding the wires. The reason is explained within this answer, electronics.stackexchange.com/questions/648991/… | |
| Apr 6, 2023 at 22:32 | history | asked | davegravy | CC BY-SA 4.0 |