I've yet to see one or hear of a confirmed case of one that does 100mA current limiting.
To increase the cost and complexity on such an otherwise simple design just to do proper enumeration that is not needed in practice would just be silly.
Server motherboards and workstation grade motherboards. There are several ones.
Now, the enumeration isnt hard.. Slap on an ftdi232 chip and set the current limit in the eeprom to 500 mA . Done. And you can now control the supply through a serial port , or log the current consumption ! Instant chart recorder ! Now, that opens possibilities. For people that dont need that feature and are cost sensitive: dont solder the ftdi on ...
Heres a couple of other ideas.
Why waste the limited power of usb on driving power hungrey leds... Use a 2*8 lcd display. Only one
Led for backlight...
Mount the display on the underside of the pcb and mill a rectangular hole in the pcb. That protects it mechanically. The display sits inside the case and is readable through the hole. You can have ot mounted flush withe pcb.
besides an 2*8 lcd display will be cheaper than led displays and you can show more info.
Use only one retary encoder , but one with a centre pushbutton.
Turn to set parameter , push to toggle between voltage and current.
Stop turning and display switches back to read values. A little arrow on display shows what you have under control.
Top line voltage
Bottom line current
--------
> 1.45V~
0.23A
--------
> OFF ~
--------
> 0.00V
O.LD.
above thee display scenarios.
Arrow shows selected parameter ( can be toggled by pushing on encoder) the wavy line means usb is connected through ftdi and someone has talked to us to set er request parameters. This acts like a Remote' indicator on test equipment
Second scenario shows output off.. A long push on the rotary button toggles output on / off.
Third scenario shows overcurrent condition. Voltage is now zero and ammeter show overload.
Now, rush in current protection :
Make sure there is ample buffer capacitor for the regulator ! So as not to trip the pc supply if we draw peaks.
Fat capacitors on usb give problems.
Use a 100 resistor from VBus to the supply section cap. Short the resistor with a simple powermos under control of the cpu. Monitor voltage on cap at plugin.
If you use a cheap cpu like a 8051f410. That has lots of a/d channels and two 12 bit dacs.
There you go. The money i saved you on displays , an extra rotary encoder can pay the ftdi232...
I'd love to have a little supply like i just described. Especially if i can use a simple serial connection to read or set the parameters.
Coming back to usb current limiting. It is a problem. When i designed the first usb ADSL modem we had endless trouble with that. Plug in with fat capacitors . Port shuts down.. Enumerate wrong .. Port shuts down .. Do not enter sleep mode correctly .. No power at resume... And other annoyances.