USB

USB is used for two purposes:

  • power supply of 5V to all ECUs and expansions.

  • communication between ECU A and USB host.

Designing a device suitable for USB-IF certification requires to follow many guidelines. Since RAMN is not meant to be used as a “proper” USB device (such as a keyboard, mouse, etc.) we do not attempt to fulfill all USB-IF requirements. Concretely, this means there is no “VBUS filter” on the board (ferrite beads, etc.)

2-layer version

On the standard 2-layer version, the USB connection circuit simply features an RC filter between SHIELD and GROUND. A Shunt resistor can be used for simple power analysis. It is also possible to replace the shunt resistor by a polyfuse.

../_images/usb_2layer.png

USB connection circuit (2-layer version).

Warning

the 2-layer version of RAMN assumes the USB host is protected against failures of its loads (short-circuits, etc.). There is no fuse or ESD protection.

4-layer version

On the 4-layer version, the USB connection features an additional ESD protection for the USB data and power lines. It also features a polyfuse to provide additional overcurrent protection. There is still however no VBUS power filter.

../_images/usb_4layer.png

USB connection circuit (4-layer version).