Hi, All:
I have a selfpowered spectrometer which needs 250mA from a USB 2.0 port, I also have a mcu to control everything including talking to the spectrometer. I want to make life easier thus I use this following option: a usb 2.0 switch with pin rating +/-40mA working as a usb hub. Can I do that? I think the 250mA is from the power pins of USB port not from the D+/D-.
P.S. Here is my drawing:
THANKS, BOY
The switch/hub needs its own power source. A bus-powered hub should only supply 100mA per port (if it's a 4-port hub, it doesn't have a choice; it has to reserve 100mA for each of the other three ports, and can't draw more than 500mA in total).
Also, your device can't draw more than 100mA until it has been configured, so you can't just hardwire a 250mA load to the USB power lines.
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