Micro USB Shield - Page 1
Forum section: electronics / projects

author: Kuusou
author_rank: Regular Contributor
timestamp: February 11, 2021, 10:48:23 am
content: I'm using a micro USB to charge a lipo and I'm unsure whether or not I should have the shield connected to ground. The board is a two layer board, power and signal traces on the top layer, common ground on the bottom. I tried looking this up but I'm still unsure what's best in this situation. Below are my schematic and PCB layout. I should add that I ordered some test boards that did NOT have the shield connected to ground and I was having some strange intermittent issues with the charging leds flickering. I'm not sure if my soldering is the issue or perhaps it's because the shield wasn't grounded. Any help/clarification on this would be very much appreciated.

author: rs20
author_rank: Super Contributor
timestamp: February 11, 2021, 11:13:42 am
content: The internet says that the USB spec says that at the device end, the shield should not be connected to the signal ground.EDIT: Don't browse the internet at 10pm, kids!In any case, not connecting the ground would never cause intermittent issues with LEDs, except in the most contrived circumstances. Hook up an oscilloscope to monitor the voltage on V+ to see if drops in the voltage supply are the cause of your LED flickering, and go from there.

author: mon2
author_rank: Frequent Contributor
timestamp: February 11, 2021, 11:31:47 am
content: Download and review the schematics for the Arduino boards. Suggest for you to follow the same method of shield grounding.

author: PeteH
author_rank: Unknown
timestamp: February 11, 2021, 12:45:27 pm
content: Probably unrelated but... What's the annular ring on those vias? (Via pad vs drill size?)Shield of the cable should be tied in well to circuit return (reference for the data signals/power in the cable) with a very low impedance. (For EMC)

author: wraper
author_rank: Unknown
timestamp: February 11, 2021, 01:05:58 pm
content: Quote from: rs20 on February 11, 2021, 11:13:42 amInternet says a lot of BS. And crap that people often do with USB ground is insane. Arduino UNO is one of the worst and stupidest examples. Unless you really know what you are doing for certain reason, connecting both GND pin and shield to GND is the safest way to proceed.

author: Kuusou
author_rank: Regular Contributor
timestamp: February 11, 2021, 01:15:37 pm
content: Quote from: wraper on February 11, 2021, 01:05:58 pmThank you for the simple answer, I appreciate it!

author: T3sl4co1l
author_rank: Super Contributor
timestamp: February 11, 2021, 03:58:58 pm
content: Does anything else connect to the board? Is it literally just charging a dumb battery?Grounding shield is the safer thing to do, from an EMI perspective. I'm not aware of a host that doesn't ground the GND wire and shield internally, and therefore it is safe to do at the device end as well.Tim

author: Monkeh
author_rank: Super Contributor
timestamp: February 11, 2021, 04:50:38 pm
content: Quote from: rs20 on February 11, 2021, 11:13:42 amThe internet should read the USB spec.Quote

author: deskpro256
author_rank: Contributor
timestamp: February 12, 2021, 07:40:42 am
content: Well, if you are unsure, then test your device. Connect it with a wire to your signal ground, see if the problem persists.I've always connected the shields to signal ground, because otherwise you have a floating metal chunk on your device, which can't be good.What charging chip are you using? TP4056? MCP73831?If it's just a battery charging PCB and not some super secret project, you can show more than the connector, because I don't think that will be the problem. Could also be 50/60Hz pickup from around the house, some stray capacitance or anything really. Maybe I'm talking out of my ass.I've had TP4056 LED's bugging around if I touch the battery terminals(without the battery connected).Also, if you are interested check out this video by Robert Feranec with Rick Hartley about grounds in PCB's, EMI and shields. The link will lead to the section about shields on connectors, but check out the whole video too as it has a lot of interesting topics regarding PCB design.https://youtu.be/vALt6Sd9vlY?t=2836

author: mayor
author_rank: Regular Contributor
timestamp: February 12, 2021, 10:32:39 am
content: FTDI USB hardware design guidelines app note(https://ftdichip.com/wp-content/uploads/2020/08/AN_146_USB_Hardware_Design_Guidelines_for_FTDI_ICs.pdf) states:"As noted above, USB consists of power, ground and two data signals. In addition, the USB connectorprovides connection to the shield on the USB cable. Over the years, FTDI have experienced that ondesigns where a standard USB A-B or A-miniB cable is in use, such as with the USB-COM232-Plus1, it isbest to avoid directly connecting the USB shield and signal ground on the PCB. Provide pads for a zero ohm resistor for a DC path or capacitor for a high-frequency path between shield and signal ground. Thisallows flexibility in the best component selection to minimize signal noise while providing EMCcompatibility. "

author: wraper
author_rank: Unknown
timestamp: February 12, 2021, 11:41:43 am
content: Quote from: mayor on February 12, 2021, 10:32:39 amThey forgot to say that if you disconnect the shield from the GND on PCB, itmust be connected to grounded metal enclosurewith conductive gasket or something similar. And here comes the shit people make. They disconnect shield from GND on PCB and do not connect it to anything else.