USB current??? 2

[Andrea1984]

Hello to everybody,
it's the first thread i open here, and i hope you'll be able to help me...

I always knew that USB standard allows a current to be sinked of 500mA...great surprise today when i realized that connecting my HTC Tatoo to the Notebook USB port it sinked 780 mA...
Am i crazy? Is this normal? Shouldn't the USB port be limited to 500mA? Otherwise...what am i missing?

Thanks in advance for your helpfull answers..

Best regards,

Andrea

 

[VEBill]

It's good to know "the rules", but equally important to be aware of the exceptions.

Not all USB products religiously follow "the spec", and current limits is one area where I've seen explicit mention of exactly that in the product manuals.

 

[IRstuff]

Part of the disparity in performance is simply due to the fact that the USB spec was intended for a much simpler set of potential peripherals.


TTFN

FAQ731-376

 

[MacGyverS2000]

Sorry but i don't understand what you mean...warning about what?

I wanted to warn you that this thread may get red flagged (RF'd) and deleted. This site is meant for practicing engineers to discuss work-related issues, though you may often see familiar faces dabbling in areas outside their area of expertise on a curiosity or hobby basis. Non-familiar faces (i.e., those who have very low post counts) posting hobby type questions do not normally receive such latitude and the threads are often removed. This thread is of that type, but the information being posted is of enough interest to the "familiar faces" that it's being left open, at least for the time being. Get the info that you need, but be forewarned that if it strays too far into hobby territory it may still be RF'd.

Dan - Owner

http://www.Hi-TecDesigns.com

 

[itsmoked]

The stated goal and driver for USB 3.0 is to provide download of a full length HD movie in 90 seconds or less. It was felt that if it took longer than this the average attention span would prevent common usage for this application.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[Noway2]

This thread made me curious and so I just took a quick look at several data sheets on Digikey for several Type A USB-2.0 receptacles. Some, but not all manufacturers post voltage and current ratings. I saw both 1.5A and 1.0A listed. It looks like 1.5A may be the maximum allowable, but this doesn't guarantee that the manufacturer designed to accommodate this much. Personally, I always thought that it was 500mA per circuit. I also recall that there is a (lesser?) limit that the device must comply with until it has been enumerated and given the go-ahead from the host to draw more.

 

[Skogsgurra]

Yes, that is the 200 mA that you can draw without asking for 'permission'. When communication is established, you ramp the supply to the rest of the circuitry. My experience is that also the 200 mA is enough to power lots of different circuits.

Gunnar Englund

http://www.gke.org

--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[Andrea1984]

Hi everbody,
since i opened the thread i wanted all of you knowing how it finally ended...
In the user manual of the car there was no indication about the maximum current allowed for the USB device connected to the AUX input, so i tried and...luckly nothing exploded or went on fire...
Being like this i finally suppose that each manufacter put its own a limit to the maximum current allowed and, probably, the 500mA limit is, in the most of the case, valid just for the communication devices...for charging and similar the limit may vary from one manufacter to the others.

Hoping this thread may be helpfull for other people in the future, i thanks again all of you for your helpfull answers.

Best regards,

Andrea

 

[zappedagain]

Here is a timely article:

http://www.powermanagementdesignline.com/showArticle.jhtml?articleID=222301007&cid=NL_pmdl

John D

 

[zalim]

I think the limit varies w.r.t the applications.

EngineerForum.Net

 

[amptramp]

For anyone interested, here is an article discussing USB 3.0.

http://electronicdesign.com/article/components/usb_3_0_the_next_generation_interconnect.aspx

 

[Noway2]

This weekend I happened upon a practical example of this discussion thread. My cell phone, bless it's soul, froze to death after getting left in a pile of snow for over a week and had to be replaced. Yesterday I purchased a new one and discovered a new(?) feature that it is chargeable by way of the PC USB port. I suppose this is to overcome the limitation where your ability to use the phone an an Internet 'modem' is limited by your battery which gets sucked dry by the data transfer.

Apparently when you plug the phone into the USB port of the PC, the charger wants to draw some serious current, at a level which is beyond the default capabilities of the USB port. This causes a warning message to pop up on the phone when it is connected to the PC. In order to make it work correctly, you need to run a little utility program that reconfigures the USB port to allow current draws of up to 1A. I wasn't aware that you could reprogram the USB ports to do this, but I thought of this post when I was trying things out.

Note: the Commercial Windows application that comes with the phone does this automatically. As a Linux enthusiast, I had to find an application and perform this function manually.