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Maximum current when power taken from USB cable

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engr_joni_ee

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Hi,

I have devices which include Microcontroller and FDTI chip on the development board. I am going to power them up from +5V and GND available in the USB 2.0 cable, I guess this configuration is self power with maximum current 100 mA.

I am wondering in which configuration 500 mA current can be drawn from USB, any example ?
 

Up to 500 mA can be requested in the device descriptor. The disadvantage is that devices with > 100 mA power requirement are possibly not supported by a bus powered hub. Hosts and self powered hubs should support it.
 

If I connect some devices on the development board directly to +5V from the USB cable without any device descriptor then how much maximum current can be withdrawn from the USB cable ?
 

Hi,

without any device descriptor
Click to expand...
Don´t ever draw more than 500mA.

Mind:
This is against USB specification. Please avoid this if you plan it for a commercial product.

Klaus
 

The upstream port may switch off the device if the current specified in the device descriptor is exceeded. In practice it's rather unusual.
 

In case of bus power (devices on the development board power up from the +5V Vbus of the USB cable) how much maximum current the USB bus power can provide. I guess 500 mA. is that right ?

Because I know in case of self power (devices on the development board power up with external power supply and also connected to Vbus for device enumeration) the maximum current is 100 mA.
 

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