Question on Current limit of a USB distribution switch...!

[malli_1729]

I have Question regarding the Current limits of USB2.0 COmplaint Power distribution switches...

From my understanding, the maximum current drawn from any USB port by a peripheral is 500mA. Please correct if i am wrong.

I Have seen USB power distribution power switches datasheets like MIC2077 or TPS2041A etc, the datasheet says
it can give minimum 0.5A, but electrical specifications says Current limit Typ 1A Max=1.2A.

So, they can give upto 1A max, then only they will raise the Over Current Flag, But as per USB standard, each peripheral should consume only 0.5A....

Why this confusion..... Please help me to correct if i am wrong.....

 

[BradtheRad]

I have not attached homebrew devices to a USB port so I don't know particulars about your device...

What I have seen with USB portable hard drives is that the USB cable has a Wye-jumper which goes to a second USB port, in order to supplement the power draw, so the drive can operate.

The same kind of workaround could enable your device to get additional power.

 

[PedroDaGr8]

This is not quite true. USB defines two separate current limits (which have been changed in USB3.0). There is the data transmission current limit and the charging current limit. Data transmission limit is the maximum power current allowed while the data connection is maintained between the two devices, this limit is the 500mA that you quote. The charging current is the maximum current allowed when there is no data connection (this is enabled by shorting both data pins to each other and/or to ground, I forget which). Traditionally, the charging limit was 900mA-1A but recently it has been increased to 1.5A with some devices supporting even larger currents such as 2.1A (apple devices mainly but many other tablets now do as well).