USB Interface Question

[Boon_NZ]

I am planning to use a FT245BM device from FTDI to add USB connectivy to my circuit.

However, I will be completing some battery charging using USB also (MAX1811). The USB specifications state that no more than 100mA cannot be drawn until the device is enumerated and that it can be configured as a high power device (upto 500mA) via enumeration.

My question is, are these figures guidelines or are they limits. Could a device source more than 100mA at startup and still connect correctly? Could it draw 200mA without configuring as a high power device? I realise this will not be within the USb spec but will it work?

Your help would be greatly appreciated!

 

[Wizzard]

Hi

Most computer will supply current even without proper configuration
Look att all those extarnal fans and ligtbulbs etc, https://www.everythingusb.com/hardware/Offbeat_USB_Gadgets/

but my Toshiba for example will shut of the 5 volt to protect the computer from damage if current drawn and enumeration dosen't match

/Wizzard

 

[kasd]

If you are design something out of the USB specs, it may work for some PCs but not work for others.