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USB powered devices

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frag85

Post subject: USB powered devices

Posted: 17 Nov 2013, 06:53

Joined: 01 Jul 2010, 20:01
Posts: 77

Anyone know of a USB cable that enumerates (to draw full power from the port)? I've heard of programmable chips from companies such as FTDI which I guess would be possible to use in this case (although I'm not sure exactly what I need quite yet), but I'd like to keep it as simple as possible and keep things in spec.

I know you can 'cheat' the port and draw over the spec of 100mA (without enumerating). Hell, I've been doing this for years now with a device I'm that I am getting to the final stages to put on the market. There are plenty of other devise out there; like chargers, coffee cup warmers, toys, ect... that draw >100mA as well. But as of right now I don't want to be one of those that don't follow the rules and abuse the standard. There is some good reading here on MaximIntegrated.

I am looking to sell a USB powered device that requires around 185mA of power and don't want to take any chances with someone else's hardware and want to be certain my device works on any powered port, USB 2.0 or 3.0.

EDIT: I've redesigned a few aspects and got things down to <100mA, so I should be fine. But if anyone knows a good place for a chip to control the power from the hub, i'm still interested!

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Haldi

Post subject: Re: USB powered devices

Posted: 17 Nov 2013, 13:16

Editors

Joined: 08 May 2011, 18:58
Posts: 2286

Quote:

A unit load is defined as 100 mA in USB 2.0, and 150 mA in USB 3.0. A device may draw a maximum of 5 unit loads (500 mA) from a port in USB 2.0; 6 (900 mA) in USB 3.0.

So it was 500mA! If you use 5 units loads can you use the databus anymore or what ?

my mainboard also has these "powered" charging USB ports, they can do up to 1.5A but i guess not every PC has these.

source: http://en.wikipedia.org/wiki/USB

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Gilly

Post subject: Re: USB powered devices

Posted: 30 Nov 2013, 09:58

Insiders

Joined: 15 Apr 2005, 23:27
Posts: 1172

Yeah, the "charging ports" are something you need to turn on in the BIOS. Not all boards have it.

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