# Help me interpret this part of the USB + Power Standard

It's the last two sentences of this section:

What does the last sentence mean exactly? And how do I apply it?

Basically I am building a USB + Power peripheral that will convert USB to RS-232 and drive a display that needs more than the 500mA you get from regular USB, hence we are using USB + Power. You can find the full standard here:

http://www.poweredusb.org/pdf/PoweredUSB_v08g.pdf

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You should consider accepting some of the answers to your previous questions. A 0% accept rate is essentially telling people you ask for helping and don't give thanks where thanks are due... which is a good way to ensure that a lot of the people here won't bother wasting their time writing up an answer for you. Just some friendly advice. :) –  Toby Lawrence Sep 22 '12 at 1:34
The text you quote contains a lot of requirements. Which one in particular are you unsure off? If the answer is 'all' I suggest that you are not the right person to be involved in the design. –  Wouter van Ooijen Sep 22 '12 at 13:58
Thanks for the advice. It has been taken care of. –  Gustavo Corona Sep 23 '12 at 0:32
The last sentence only. Sorry I didn't specify. –  Gustavo Corona Sep 23 '12 at 0:34

The statement means:

Max continuous DC current drain not to exceed 1.5A.

If the current pulses briefly to more than 1.5A it should do so for no more than 10 mS

If it pulses to more than 1.5A repetitively, even if the pulses are <= 10 mS long, the RMS (~= mean or average here) current drain should not exceed 1.5A overall. eg if it pulses to 3A for 10 mS a number of times in a row the off time average should be >= 10 mS in order to keep average drain under 1.5A.

The rise time limit of 10 mA/uS = 10,000 A / second is the MAXIMUM rate at which current draw should change. (Language suggests it may be a minimum :-). ) Ideally this will be arranged in a formally controlled manner.

IF rise time is not formally controlled then the result should be no worse than suddenly connecting a 2200 uF capacitor with ESR = 80 milliOhms across the USB 5V rails.

And how do I apply it?

Engineering.

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