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USB current???
2

USB current???

USB current???

(OP)
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

RE: USB current???

2
If it's not communicating at the time, you're allowed to supply as much current as the connector can handle (assuming it's a host or a hub downstream charging port).  For USB 2.0, the standard socket is designed for 1.5A.

Dan - Owner
http://www.Hi-TecDesigns.com

RE: USB current???

Now, that's a piece of information that I also could use!
Thanks a lot.

Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

RE: USB current???

If I remember correctly the device has to ask for the power.
It asks for it in units of 100ma in 2.0 and 150ma in 3.0(usb on the go)(Up to 5 units per device). I also think the max power can change depending on the communication speed.
 

RE: USB current???

I have kept power below 200 mA in all applications and ramped up to a maximum of 500 mA when device found by the PC. Is that old, outdated, no-good-anymore information?

Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

RE: USB current???

As stated above, there are restrictions as to how much current inrush current is allowed.  Similarly, there are requirements on the host side that govern the transient response (sag) of the +5V line.  The specs even indicate the load characteristics that it must hold up to. From what I recall from when I last did a USB project, this is a common source of trouble when attempting to certify a USB complaint device or controller.

Under normal operating mode, the device must request how much current it wants to draw up to 500mA.  Since the value used to communicate this is byte wide, each unit of specified current represents 2mA.

 

RE: USB current???

I've got a wifi router that permits higher than normal current on the USB port because the designers know that 3G Internet sticks need more than 500mA.

And many such sticks come with a 2-plug cable to draw power from 2 sockets if connected directly to older laptops that enforce the 500 mA limit.

Another older stick I used to have contained a battery to solve the peak power issue.

 

RE: USB current???

(OP)
Thanks a lot for your very fast replies...but i explain you better why i'm worried about this argument.

I'd like to recharge the battery of my HTC using the AUX input (actually a USB Socket)of my Ford Fiesta car , but i'm worried that HTC asking for more current than the standard one of USB may results in damaging the AUX input in my car...

Do you think the current would simple be limited by the USB (AUX) controller or that some damage may occur?

Thanks a lot again,

Andrea

RE: USB current???

I'd be a lot more worried about a laptop than a Ford in terms of the amount of current that can be provided.  Automakers usually try to make systems fairly robust with a healthy safety factor due to liability and the "wide range" of people who buy cars.  

I'm guessing the Fiesta's USB port can take care of itself.  

There is an Automotive forum on this site you could try.  

David Castor
www.cvoes.com

RE: USB current???

Some replies above describe hand shaking, but don't clearly mention that it's optional.

USB ports will provide power to even the simplest device. A simple, completely mindless, USB-powered device can draw power from any common (USB 2.0) socket. Hand shaking is obviously optional.

In fact, some USB-powered toys have two wire (power only) cords, no data wires. There's even a USB-powered coffee cup warmer, nothing more than a 10 ohm, 2.5 watt resistor.




  

RE: USB current???

(OP)
Hi VE1BL,

uyou percetly took the point...I don't mind about the communication while charging  the device...i just wanted to know what is the current limit of a USB host...
So do you all agree that it should be 1,5A when there is no communication? May you tell me if there is some official document on the internet saying this?

Thanks a lot to everybody for helping

Bye bye

Andrea

RE: USB current???

"So do you all agree that it should be 1,5A..."

Not me. I've seen too many instances where the limit (for USB 2.0) was described as being "500 mA".

And I've seen several explicit exceptions where the product info states that the ports provide more than (again) "500 mA" - typically to support 3G Internet sticks.

But USB power ports, such as the little white power cube provided with iPhones, provides 1A.

It's a classic case of YMMV.

Have you checked the car's manual?

 

RE: USB current???

There are rules to the power capabilities I listed above, but they're in the spec, so read it.

Noway, 3.0 ups the specs a bit, but only a few compliant devices have hit the shelves yet... I think only a single motherboard has been offered, and I've seen a handful of devices like hard drive docks, etc.



BTW, I just noticed this is not an engineering design, sounds like a home project... this thread may disappear soon.

Dan - Owner
http://www.Hi-TecDesigns.com

RE: USB current???

I see no reason to RF this thread. Good information that seems to be new to a bunch of people - including me.

Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

RE: USB current???

(OP)
I see no reason to RF this thread


Sorry but...what does RF stands for in this sentence? :)

RE: USB current???

Gunnar,

I didn't for the reason you mentioned, but I wanted to warn in case someone did (as well as remind Andrea that this site is for practicing engineers and hobby projects as a first post can get you booted).

Dan - Owner
http://www.Hi-TecDesigns.com

RE: USB current???

(OP)
Gunnar,

I didn't for the reason you mentioned, but I wanted to warn in case someone did (as well as remind Andrea that this site is for practicing engineers and hobby projects as a first post can get you booted).  

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

RE: USB current???

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.

 

RE: USB current???

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: Eng-Tips.com Forum Policies

RE: USB current???

Quote (Andrea1984):

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

RE: USB current???

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

RE: USB current???

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.
 

RE: USB current???

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

RE: USB current???

(OP)
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

RE: USB current???

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

EngineerForum.Net

RE: USB current???

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.  
 

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