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I have a Logitech keyboard which has two USB ports. I am using the keyboard with a MacBook Pro 15" (late 2011).

When I try to use the USB ports on the keyboard (say I plug in my iPhone), I get this error:

enter image description here

"A USB device can't draw enough power to operate properly. If the device came with a power cord, plug it into an electrical outlet. Otherwise, connect the device to a USB port on your computer."

Any suggestions on fixing this issue?

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What else have you tried plugging in beside the iPhone? Can you provide the specific model number of the keyboard? – iglvzx Jul 28 '12 at 2:20
1  
Well, an iPhone specifically needs more watts than the keyboard is outputting. You should be plugging it into the back of the computer. – Randolph West Jul 28 '12 at 2:55

2 Answers

up vote 2 down vote

There is only so much power available on the the USB Bus to power Devices, An iphone needs a decent amount of power to charge and some of that power is already being used to power the keyboard. so it is requesting more power from the bus then the bus can provide.

Also on your MacBook Pro all USB ports aren't created equal, depending upon the port you use, it may have less power available since it is being shared with some internal USB devices (such as the webcam and SD card reader).

To find out which ports are being shared with which devices, plug in a known USB device and open System Information (System Profiler on older versions of OS X). In Hardware > USB, find the known device in the USB Device Tree. Check whether there are other devices sharing the same USB High-speed Bus. If the port in question is being shared, you might try charging on a different port.

Also take a look at Apple Menu -> about this mac -> more info -> system report

Look at the usb info, it will show you how much power is provided / available.

If you want to plug the iphone into the keyboard and the keyboard doesn't have enough power or the hub in it isn't powered, you will need to purchase a powered USB hub, and then plug that in. The powered hub will have a wall wart that provides power via the usb ports.

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up vote 1 down vote

I had this problem a few weeks ago after upgrading to OS X Lion. To fix this problem, I had to reset the System Management Controller (SMC) and it seems to work fine after that.

This guide should help you reset the SMC. http://support.apple.com/kb/HT3964?viewlocale=en_US

If that doesn't work, I would suggest resetting PRAM and NVRAM as well, you can find the steps here:

http://support.apple.com/kb/ht1379

I hope this solution works for you.

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Whilst this may theoretically answer the question, it would be preferable to include the essential parts of the answer here, and provide the link for reference. – Luke Jul 30 '12 at 19:39

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