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doc: improve doc, fix current limit

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King Kévin 2022-06-16 18:03:29 +02:00
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README.md
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@ -3,7 +3,7 @@ the CuVoodoo USB hub is a 7-port USB 2.0 hub meant for device testing.
purpose
=======
most USB hub are super cheap and crappy, leading the poor connection connection and data transfer.
most USB hub are super cheap and crappy, leading to poor connection and data transfer.
there are industrial USB hubs, but they are bulky and very expensive.
to solve this issue I decided to design my own USB hub, tailored to my needs.
@ -18,7 +18,7 @@ this device is a 7-port flat USB hub, preventing reaching this limit too often.
the incoming and outgoing USB ports are individually ESD protected.
this safety becomes important when developing, testing, and handling bare electronic devices.
this also comes in handy against when connecting circuit with different ground potentials.
ESD protections already saved my day twice.
ESD protections already saved my day twice this way.
the issue is that they can blow without you noticing, but at least they protected the device once.
each output port is current limited to 500 mA.
@ -34,17 +34,17 @@ this is an important requirement when developing and testing devices, which requ
additionally, a switch next to the power can force the power off state.
the USB hub can be self-powered (through the USB input port), externally powered by 5V, or externally powered by anything between 6 and 40V.
this allows to use higher voltage power supplies to provide enough current to all power.
this allows to use higher voltage power supplies to provide enough current to all ports.
the 5V are not feed back to the host.
each output port comes with a high voltage output power port, connected to the high voltage input port.
each USB port comes with a high voltage output power port, connected to the high voltage input port.
this allows to power devices which require more than 5V (e.g. 12V externally powered devices).
each of these power output is controllable.
these power outputs are controllable.
as with the 5V USB power output, this allows to remotely switch on an off individual devices.
each port has status LEDs, indicating the speed and power of the connected device.
each port has status LEDs, indicating the speed and power status of the connected device.
the board uses proper impedance and differential signal routing to provide clean USB transfer.
the board uses proper impedance and differential signal routing to provide clean USB signal transfer.
design choice
=============
@ -67,16 +67,24 @@ and it is easier to solder thanks to its TQFP package, and provides all required
sadly I could not find a source for the 64-pin packages, and the 48-pin variant does not provide all required functionalities.
thus I had to fall back to the Microchip USB2517, which uses a harder to solder QFN package.
power control
-------------
some USB hub chips allow to remotely control the power output on individual ports.
this capability is here also used to control the power on the higher voltage output.
thus you can completely power off even larger target devices.
current limitation
------------------
the few USB hubs that have current limitation on the output, use a MIC2026.
very few USB hubs that have current limitation on the output.
this does limit the current to 500 mA, but only in constant current mode.
the fault is reported (e.g. to the hub, back to the computer), but it is up to the user to power off the faulty device.
instead I use poly-fuses, which automatically cut the power once the limit of 500 mA is reached.
this is faster, and removes user-based actions.
the fault is still reported.
if well designed, the fault is also reported to the computer.
sometimes the hub also turns off the power, or it is up to the user to power off the faulty port.
on this hub, the fault is reported, and the power is automatically disabled, preventing damages on the device due to prolonged shorts.
this is very useful when testing devices.
the power is restored once the current limit is cleared.
LED color
---------