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I'm using Beaglebone Black. How much power can I provide over USB to an external device?

I have read the specifications, and the information I found was 2 amps to the board should be good enough to power external device. What I don't know is how much power can be delivered to the external device? I could not find that in my research.

JYelton
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Timothy Clemans
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2 Answers2

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The BBB uses a TPS2051 USB Power Switch. It limits the USB Host port power to 500mA on the high end. The power is drawn from the same system bus that powers the rest of the 5v parts, the 5v input port.

The BBB needs 1A for normal function + a low current usb device (keyboard, mouse, things that draw little current). Using a Cape or a high current USB device would require a power supply that can meet or exceed that extra current draw.

Passerby
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  • Argh, if the OP hasn't done any research at all, just straight-up answering encourages that kind of behaviour. – Connor Wolf Oct 08 '13 at 04:49
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    The downvote button for the question can be found next to the question. Please do not confuse question voting with answer voting. – travisbartley Oct 08 '13 at 05:06
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    @Connor I completely agree... **but** suppose someone searches for the same problem and finds it here at EE.SE with a good answer. We make it *easier* to do preliminary research for future visitors. So maybe we spoil one OP, but potentially help many others proactively. – JYelton Oct 11 '13 at 16:35
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    @JYelton I came here from Google with the same question, so keeping this thread around was helpful :) – Gourneau Jun 13 '14 at 05:36
  • What happens if you plug in a usb device that draws too much current? – user391339 Nov 16 '14 at 06:00
  • @user391339 the tps2051 signals an over current condition, and attempts to go into constant current mode, providing a variable voltage to the load. – Passerby Nov 16 '14 at 07:39
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    Hmm. My rev c board will no longer power up after hot plugging in a usb wifi dongle. Be careful! – user391339 Nov 16 '14 at 10:15
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Unless you know explicitly otherwise, assume the maximum power is 100 mA.

If your external device isn't just using the USB interface for power, and is actually enumerating to the beaglebone properly, it can request up to 500 mA under standard USB.

If the beaglebone supports some of the non-standard USB-2.0 high-current charging profiles, any device that also supports the non-standard charging profiles should just work, or fall back to only 500 mA draw automatically.

Anything else is technically a violation of the USB spec's behaviour.

It should be noted that a LOT of hardware out there just treats USB connections as a dumb 5V power source, which usually works (except when the host properly monitors device current draw). Hardly anyone actually implements proper host-based current monitoring, because it would break lots of non-spec hardware, and most users would just go "why doesn't your device x work with my (actually broken) shitty MP3 player/keyboard fan/stupid USB widget.

In practice, you can generally draw 500 mA even without enumerating. Drawing any more current depends entirely on the USB host, and is implementation specific.

Fortunately, in this case, the beaglebone's schematics are available, so you can look and see what the USB current-limiting mechanism is yourself.

The USB interface is on page 4 of the schematic.
Hint: The USB power for the host-port is switched by a TPS2051B

Connor Wolf
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    OP's Q:"How fast can my model x car go?" Your A:"The speed limit is 55 mph". – Passerby Oct 08 '13 at 04:35
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    @Passerby - Did you not read the whole answer? OP is very poorly researched. If he wants something more specific, he needs to show he at least looked on google first. – Connor Wolf Oct 08 '13 at 04:38
  • Also, I was adding to the answer as you commented. – Connor Wolf Oct 08 '13 at 04:42
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    I think he did do some research, but could not find the answer because the specification needed is in TPS2051B specs, not the BBB specs. It is an innocent question and I wouldn't fault him for it. And I honestly don't see why either one of these answers are downvoted. – travisbartley Oct 08 '13 at 05:18
  • @trav1s the downvote was based on the answer before it was edited. – Passerby Oct 08 '13 at 05:38