0
\$\begingroup\$

It's the last two sentences of this section:

enter image description here 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

\$\endgroup\$
  • \$\begingroup\$ 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. \$\endgroup\$ – Wouter van Ooijen Sep 22 '12 at 13:58
  • \$\begingroup\$ The last sentence only. Sorry I didn't specify. \$\endgroup\$ – Gustavo Corona Sep 23 '12 at 0:34
2
\$\begingroup\$

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.

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.