Both good ideas !

I had the regulator always on, because I wasn’t sure about the power up sequence/allowable delay when it comes to USB 2 devices …

I like the idea of the enable pin though J




The best executive is one who has sense enough to pick good people to do what he wants done,

and self-restraint enough to keep from meddling with them while they do it.

Theodore Roosevelt


From: Alex Gibson []
Sent: Thursday, January 27, 2011 5:24 PM
To: General mailing list for gumstix users.
Subject: Re: [Gumstix-users] External Power for USB


Why not have the fet in front of the regulator so you only power the reg when its needed. ?
If you aren't powering the rest of the gumstix from it unless you need the usb powered all the time.

The LP3873/LP3876 (LP3873ET-5.0) are nice
and having a shutdown/enable pin is handy


On 28/01/2011 5:28 AM, William Pretty Security Inc wrote:

First of all I’m more of a hardware person, so my solutions tend to be hardware based J


That being said, here is my proposed solution:


In the attached schematic, you use the +5V from the USB input connector as a logic signal to turn on the FET.

Because FET’s are voltage controlled devices, it takes very little current to turn them on J


If you use a high current FET and a high current supply you could supply AMPS to the USB device JJJ


What do you guys think ??



"People sleep peaceably in their beds at night only because rough men

stand ready to do violence on their behalf." - George Orwell


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