mirror of
https://github.com/FunKey-Project/FunKey-Project.github.io.git
synced 2025-12-12 18:28:51 +01:00
56 lines
2.6 KiB
Markdown
56 lines
2.6 KiB
Markdown
In the **FunKey S** device, the USB interface has 2 functions:
|
|
|
|
- provide an external power supply source for both powering the
|
|
device and charging the built-in LiPo battery
|
|
- provide a data interface to transfer firmware upgrades,
|
|
configuration files, game emulators and game ROMs
|
|
|
|
The first function only requires the +5V USB power and GND pins. The
|
|
second function requires to wire the additional differential data
|
|
lines D+ and D-. As we only need to operate as an USB device and
|
|
although the V3s is able to work as either an USB host or USB device
|
|
using the USB OTG protocol, we don't need the ID pin to determine by
|
|
the cable wiring which role we must take.
|
|
|
|
{: align=left }
|
|
|
|
The main part is of course the [Micro USB edge-mounted connector][1]
|
|
**J2**, which we chose in order to "mask out" its already low-profile
|
|
height into the PCB thickness. And with its "harpoon-like"
|
|
through-hole legs, it should avoid tearing it off the board if the
|
|
user don't pull the chord straight.
|
|
|
|
The USB schematic is the following:
|
|
|
|
{.lightbox}
|
|
|
|
Before connecting 2 devices using an USB cable, they may be at
|
|
completely different absolute voltages, and during cable insertion,
|
|
the shield will be in contact before the other pins, including
|
|
GND. The **C6** capacitor between the Protective Earth (Shield) and
|
|
GND is here to provide an AC path for sinking this difference in
|
|
voltage and align the GND levels when plugin the cable.
|
|
|
|
The resistor **R4** on the USB ID connector pin should probably not be
|
|
mounted: as we act only as an USB device, this pin should be left
|
|
floating.
|
|
|
|
The capacitors **C7**, **C8**, **C10** and ferrite bead **L2** form a
|
|
constant-k 3 pole CLC low pass filter to remove any spurious in/out on
|
|
the USB power supply wire. The USB 2.0 specification limits the
|
|
maximum bulk capacitance value to 10 µF in order to avoid power supply
|
|
excessive droops when plugin in a device with a discharged large bulk
|
|
capacitor.
|
|
|
|
**D15** is a [NXP PRTR5V0U2X,215][2] combined TVS protection diode for
|
|
the VBUS pin and a set of clamping diodes that will limit the voltage
|
|
on D+ and D- pins to stay between GND and VBUS levels to in order to
|
|
protect the V3s USB driver from under / over-voltages.
|
|
|
|
[1]: https://github.com/FunKey-Project/FunKey-S-Hardware/blob/master/Datasheets/C40958_MICRO5P%E6%B2%89%E6%9D%BF%E5%BC%8F0.8%E5%9B%9B%E8%84%9A%E5%85%A8%E6%8F%92%E6%97%A0%E5%AF%BC%E4%BD%8D%E6%9C%89%E5%AD%94%E8%80%90%E9%AB%98%E6%B8%A9_2016-05-20.PDF
|
|
[2]: https://github.com/FunKey-Project/FunKey-S-Hardware/blob/master/Datasheets/C12333_PRTR5V0U2X%2C215_2017-10-31.PDF
|
|
|
|
--8<--
|
|
includes/glossary.md
|
|
--8<--
|