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Power rating on Laptop USB ports

Discussion in 'Laptops' started by Clive, Jul 26, 2006.

  1. Clive

    Clive Guest

    Are all USB 2.0 ports on Laptops rated at 500ma?

    I have several Freecom USB 2 drives that require a 500ma port - so they will
    run without need of a power supply


    thanks

    Clive
     
    Clive, Jul 26, 2006
    #1
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  2. Clive

    Guest

    Clive wrote:
    > Are all USB 2.0 ports on Laptops rated at 500ma?


    The USB spec says a root hub should supply 500mA. Empirically, many
    portable machines do not supply this much.

    Also, a 2.5" hard disk requires more than 500mA peak current to start
    up. So bus-powered HDDs are almost always relying on being able to
    squeak a brief pulse of 1.5 A or more out of the port before it shuts
    down.
     
    , Jul 26, 2006
    #2
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  3. Clive

    SMS Guest

    Clive wrote:
    > Are all USB 2.0 ports on Laptops rated at 500ma?
    >
    > I have several Freecom USB 2 drives that require a 500ma port - so they will
    > run without need of a power supply


    The USB spec is 500mA, but in reality, the over-current trip limit is
    usually set to 1000mA.
     
    SMS, Jul 27, 2006
    #3
  4. Clive

    budgie Guest

    On Wed, 26 Jul 2006 20:23:25 -0700, SMS <> wrote:

    >Clive wrote:
    >> Are all USB 2.0 ports on Laptops rated at 500ma?
    >>
    >> I have several Freecom USB 2 drives that require a 500ma port - so they will
    >> run without need of a power supply

    >
    >The USB spec is 500mA, but in reality, the over-current trip limit is
    >usually set to 1000mA.


    I'd believe that for desktop machines, but most laptops I've checked would crap
    out at or before the spec 500mA.
     
    budgie, Jul 27, 2006
    #4
  5. budgie wrote:
    > On Wed, 26 Jul 2006 20:23:25 -0700, SMS <>
    > wrote:
    >
    >> Clive wrote:
    >>> Are all USB 2.0 ports on Laptops rated at 500ma?
    >>>
    >>> I have several Freecom USB 2 drives that require a 500ma port - so
    >>> they will run without need of a power supply

    >>
    >> The USB spec is 500mA, but in reality, the over-current trip limit is
    >> usually set to 1000mA.

    >
    > I'd believe that for desktop machines, but most laptops I've checked
    > would crap out at or before the spec 500mA.


    This is one of the reasons that I use externally powered USB hubs to feed my
    USB powered external hard drives when ever possible. They are cheap and
    easy to replace should they crap out from an "overload".
     
    GlowingBlueMist, Jul 27, 2006
    #5
  6. Clive

    M.I.5¾ Guest

    <> wrote in message
    news:...
    >
    > Clive wrote:
    >> Are all USB 2.0 ports on Laptops rated at 500ma?

    >
    > The USB spec says a root hub should supply 500mA. Empirically, many
    > portable machines do not supply this much.
    >


    Almost.

    Paragraph 7.2.1 of the USB2 specification states that root ports *must*
    supply 500 mA.

    > Also, a 2.5" hard disk requires more than 500mA peak current to start
    > up. So bus-powered HDDs are almost always relying on being able to
    > squeak a brief pulse of 1.5 A or more out of the port before it shuts
    > down.
    >


    If they are incapable of supplying 500 mA, then they are not compliant and
    cannot claim to be USB2 (or USB1) compliant.

    Para 7.2.4.1 requires a port to provide transient current suppression.
    Transient currents must be available, but are only required to feed load
    capacitances (which are limited). Further, any transient that causes Vbus
    to depress by more than 330mV, must be signalled back to the host and the
    device de-enumerated. A message about a current surge pops up. It is not
    unkown for ports to be damaged by large surges (It shouldn't be a fuse
    because these are not allowed (Para 7.2.1.2.1)).
     
    M.I.5¾, Jul 27, 2006
    #6
  7. Clive

    M.I.5¾ Guest

    "SMS" <> wrote in message
    news:44c831b5$0$96210$...
    > Clive wrote:
    >> Are all USB 2.0 ports on Laptops rated at 500ma?
    >>
    >> I have several Freecom USB 2 drives that require a 500ma port - so they
    >> will run without need of a power supply

    >
    > The USB spec is 500mA, but in reality, the over-current trip limit is
    > usually set to 1000mA.


    The upper limit is not explicitly specified other than an absolute limit of
    5A for all the ports on a hub.
     
    M.I.5¾, Jul 27, 2006
    #7
  8. Clive

    M.I.5¾ Guest

    "budgie" <> wrote in message
    news:...
    > On Wed, 26 Jul 2006 20:23:25 -0700, SMS <> wrote:
    >
    >>Clive wrote:
    >>> Are all USB 2.0 ports on Laptops rated at 500ma?
    >>>
    >>> I have several Freecom USB 2 drives that require a 500ma port - so they
    >>> will
    >>> run without need of a power supply

    >>
    >>The USB spec is 500mA, but in reality, the over-current trip limit is
    >>usually set to 1000mA.

    >
    > I'd believe that for desktop machines, but most laptops I've checked would
    > crap
    > out at or before the spec 500mA.


    Any laptop that cannot supply 500mA through its USB ports cannot claim to be
    USB2 (or USB1) compliant (Para 7.2.1).
     
    M.I.5¾, Jul 27, 2006
    #8
  9. Clive

    M.I.5¾ Guest

    "GlowingBlueMist" <> wrote in message
    news:44c85ce0$0$94252$...
    > budgie wrote:
    >> On Wed, 26 Jul 2006 20:23:25 -0700, SMS <>
    >> wrote:
    >>
    >>> Clive wrote:
    >>>> Are all USB 2.0 ports on Laptops rated at 500ma?
    >>>>
    >>>> I have several Freecom USB 2 drives that require a 500ma port - so
    >>>> they will run without need of a power supply
    >>>
    >>> The USB spec is 500mA, but in reality, the over-current trip limit is
    >>> usually set to 1000mA.

    >>
    >> I'd believe that for desktop machines, but most laptops I've checked
    >> would crap out at or before the spec 500mA.

    >
    > This is one of the reasons that I use externally powered USB hubs to feed
    > my USB powered external hard drives when ever possible. They are cheap
    > and easy to replace should they crap out from an "overload".


    A wise precaution. Tne USB2 spec. requires the overload current limit to be
    self resetting. However, anecdotal evidence suggests that ports sometimes
    suffer failure following a current overload.
     
    M.I.5¾, Jul 27, 2006
    #9
  10. Clive

    budgie Guest

    On Thu, 27 Jul 2006 08:14:45 +0100, "M.I.5¾" <_SPAM.co.uk>
    wrote:

    >
    >"budgie" <> wrote in message
    >news:...
    >> On Wed, 26 Jul 2006 20:23:25 -0700, SMS <> wrote:
    >>
    >>>Clive wrote:
    >>>> Are all USB 2.0 ports on Laptops rated at 500ma?
    >>>>
    >>>> I have several Freecom USB 2 drives that require a 500ma port - so they
    >>>> will
    >>>> run without need of a power supply
    >>>
    >>>The USB spec is 500mA, but in reality, the over-current trip limit is
    >>>usually set to 1000mA.

    >>
    >> I'd believe that for desktop machines, but most laptops I've checked would
    >> crap
    >> out at or before the spec 500mA.

    >
    >Any laptop that cannot supply 500mA through its USB ports cannot claim to be
    >USB2 (or USB1) compliant (Para 7.2.1).


    They can *claim* compliance without actually being compliant. It's called
    marketing, and has litlle to do with truth or fact.
     
    budgie, Jul 27, 2006
    #10
  11. I doubt if a laptop maker would do that. It would make them subject to
    lawsuits from both the USB organization (which owns the trademarks) and
    also from end-users, the latter could turn into a class-action lawsuit
    that could cost hundreds of millions or billions.

    budgie wrote:
    >
    > They can *claim* compliance without actually being compliant. It's called
    > marketing, and has litlle to do with truth or fact.
     
    Barry Watzman, Jul 27, 2006
    #11
  12. Clive

    Guest

    M.I.5¾ wrote:

    > If they are incapable of supplying 500 mA, then they are not compliant and
    > cannot claim to be USB2 (or USB1) compliant.


    That is a _logo_ requirement though, is it not?
     
    , Jul 27, 2006
    #12
  13. "Clive" <> wrote:
    >Are all USB 2.0 ports on Laptops rated at 500ma?


    I thought the spec said they had to provide 100mA _unless_ the device
    connected to it _negotiated_ for more. Or am I hallucinating again?
     
    William P.N. Smith, Jul 27, 2006
    #13
  14. Clive

    M.I.5¾ Guest

    <> wrote in message
    news:...

    M.I.5¾ wrote:

    > If they are incapable of supplying 500 mA, then they are not compliant and
    > cannot claim to be USB2 (or USB1) compliant.


    That is a _logo_ requirement though, is it not?

    ----------------------------------

    No, it's a spec requirement. If you don't meet the spec, you are not
    officially allowed to claim USB compliance and are certainly not allowed to
    display the logo. The spec is very specific in many areas (and vague in
    others). For example, if the USB (A or B) connector is simply mounted the
    wrong way up, then USB compliance cannot be claimed (but often is, with the
    subtle use of words like "USB compatible" - but the logo definitely cannot
    be used). On the other hand, although the USB2 spec was designed to cover
    the increase to 480 Mbps, nothing in the USB2 spec actually says that that
    speed has to be supported. This gave dishonest PC suppliers the opportunity
    to market PCs with USB2 ports that didn't actually work at 480 Mbps and you
    couldn't touch them for it.
     
    M.I.5¾, Aug 7, 2006
    #14
  15. Clive

    M.I.5¾ Guest

    "William P.N. Smith" <> wrote in message
    news:...
    > "Clive" <> wrote:
    >>Are all USB 2.0 ports on Laptops rated at 500ma?

    >
    > I thought the spec said they had to provide 100mA _unless_ the device
    > connected to it _negotiated_ for more. Or am I hallucinating again?


    No, you are not hallucinating. The intention was that 100 mA was guaranteed
    to be supplied more on negotiation with the host. In practice, the issue
    has become extremely complex, because the enumeration of hubs and the power
    negotiation is not necessarily under the control of the host that is
    actually managing the network when you plug your peripheral in. Since many
    BIOS's support bootable USB devices, they have to enumerate and set up the
    power capabilities in order to establish if a bootable device is present.
    The hubs usually fail to notice that the driving seat is handed from the
    BIOS to windows. Most hub designs now manage their own ports directly -
    particularly hubs that are able to operate as both bus and self powered (the
    spec allows this, requiring self powered hubs to provide 500 mA and bus
    powered, 100 mA). A number of hubs will continue to supply power if their
    upstream port is disconnected (the spec did not intend this to happen, but
    was ambiguous on the point).
     
    M.I.5¾, Aug 7, 2006
    #15
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