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ddribin / piano-lights-hw

Specialized hardware to displays lights (LEDs) over piano keys
MIT License
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Isolate USB-C shield from ground #12

Closed ddribin closed 1 year ago

ddribin commented 1 year ago

There doesn't seem to be a good consensus here, but the USB-C shield should maybe be isolated from signal ground.

Some references:

Microchip: USB Type-C Layout Recommendations

Shield is connected to ground through an RC filter with unspecified R and C.

https://microchip.my.site.com/s/article/USB-Type-C-Layout-Recommendations

There should be a wide Earth Ground flood around the USB Type-C connector that connects to the connector shield pins. Earth Ground should also be tied to Digital Ground through an R/C galvanic circuit that is placed as close as possible to the USB Type-C connector (see R20 and C2 in Figure 1).

rtaImage

Atmel AVR1017: USB Hardware Design Recommendations

Shield is connected to ground through an RC filter with R=1M and C=4n7.

https://ww1.microchip.com/downloads/en/Appnotes/doc8388.pdf

Tying the shield directly to ground would create a direct path from the ground plane to the shield, turning the USB cable into an antenna. To limit the USB cable antenna effect, it is recommended to connect the shield and ground through an RC filter. Typically, R = 1MΩ and C = 4.7nF in Figure 3-5.

USB Shield and ground

PCBWay: How to add USB-C to your projects

Shield is connected to ground through a 1M resistor.

https://www.pcbway.com/blog/PCB_Design_Tutorial/How_to_add_USB_C_to_your_projects.html

However, compared to the micro USB-B two resistors are needed on pins CC1 and CC2. Then just add a 1M resistor to the connector shield. Also, you just connect the following lines (Vbus, D +, D-, GND) as you usually do with the micro USB-B. You can leave all other pins unconnected.

Arduino Forums: Should I connect Micro USB B shield to the ground?

Shield is unconnected. Should only be connected on the computer end. Thus unconnected on a device.

https://forum.arduino.cc/t/should-i-connect-micro-usb-b-shield-to-the-ground/960018/3

SparkFun: USB-C Breakout

Shield is unconnected.

https://www.sparkfun.com/products/15100 https://github.com/sparkfun/USB-C-Breakout https://forum.digikey.com/t/simple-way-to-use-usb-type-c-to-get-5v-at-up-to-3a-15w/7016

Adafruit: USB-C Breakpoint

Shield is unconnected.

https://www.adafruit.com/product/4090 https://github.com/adafruit/Adafruit-USB-C-Downstream-Breakout

Phil's Lab: USB-C Power Delivery

Shield is unconnected.

https://youtu.be/W13HNsoHj7A?t=724

Phil's Lab: USB Hub Design

Shield is connected to ground through 4n7F capacitor.

https://youtu.be/iR2hYpq0KI0?t=576

Phil's Lab: USB Headphone Amplifier

Shield connected to ground through an RC filter with R=DNP and C=2n2F.

https://youtu.be/-L-fKuAbQ9s?t=527

Dubious Creations: ESP32 LED Driver

Shield is connected directly to ground.

https://dubiouscreations.com/2021/05/04/designing-an-esp32-based-rgb-matrix-driver-and-making-500-of-them/ https://github.com/matthewlai/ESP32LEDControl https://dubiouscreations.com/2021/04/06/designing-with-usb-c-lessons-learned/

ddribin commented 1 year ago

In summary, all possible permutations are "recommended", for a device-side connection:

My guess is that the RC filter is the most robust, but also is the most difficult to layout.

I think I'm going to take a middle road, and add a single 0803 connection from shield (Earth) to ground (GND). Then it can handle every case, except the RC filter: