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'[EE:] How do you create and understandcircuits?(i.'
2007\01\28@192214 by Alexandre Guimar„es

face picon face
Hi,

   I always try to route thinking where the current will return but would
never expect that much of a difference with the points so close together and
with the blob with that small resistance. How much current was passing to
the rest of the circuit ??

Best Regards,
Alexandre Guimaraes



{Quote hidden}

> --

2007\01\28@201427 by David VanHorn

picon face
On 1/28/07, Alexandre Guimarães <spam_OUTlistasTakeThisOuTspamlogikos.com.br> wrote:
>
> Hi,
>
>    I always try to route thinking where the current will return but would
> never expect that much of a difference with the points so close together
> and
> with the blob with that small resistance. How much current was passing to
> the rest of the circuit ??


If I remember right, about 200mA or thereabouts, but 2dB is 2dB.
The concern in this circuit was that the opamps that we could afford had
really crappy PSRR at those frequencies.

2007\01\29@113714 by gacrowell

flavicon
face
Absolutely phenomenal timing Dave.  I was just this morning preparing to
do the copper fills on a board where I was reworking the switcher.  I
would have 'blobbed' those pins.

Thanks,
Gary

> {Original Message removed}

2007\01\29@114827 by Wouter van Ooijen

face picon face
> No you can't. But at least you should try.
> USB power greater than 48V could be found only in software...

But 12V is much more likely, and Olins specifies 10V caps.

What would you suggest, include a polyfuse/fuse/active current limit? So
the USB port will not die when the mosfet fails (only to die when
another USB peripheral is used that - correctly by the book - assumes
the port is current-limited)? In a former life my quality manager
repeated over and over: "quality is being good enough, and not better".

Wouter van Ooijen

-- -------------------------------------------
Van Ooijen Technische Informatica: http://www.voti.nl
consultancy, development, PICmicro products
docent Hogeschool van Utrecht: http://www.voti.nl/hvu


2007\01\29@120633 by David VanHorn

picon face
On 1/29/07, .....gacrowellKILLspamspam@spam@micron.com <gacrowellspamKILLspammicron.com> wrote:
>
> Absolutely phenomenal timing Dave.  I was just this morning preparing to
> do the copper fills on a board where I was reworking the switcher.  I
> would have 'blobbed' those pins.


:)    It does make a difference.

It's similar to a friend of mine (recently deceased) and his ham station.
Dave would be very fussy about connectors, and some of the folks in the
local ham club would give him heat over it, but he said "I know it's only a
tenth of a dB, but you loose a tenth here, and a tenth there, and pretty
soon you have some real loss. And that loss from the antenna to the radio,
that you can't ever get back."

2007\01\29@121831 by David VanHorn

picon face
On 1/29/07, Wouter van Ooijen <.....wouterKILLspamspam.....voti.nl> wrote:
>
> > No you can't. But at least you should try.
> > USB power greater than 48V could be found only in software...
>
> But 12V is much more likely, and Olins specifies 10V caps.


You shouldn't ever get anything that would bother a 10V cap, other than ESD,
and they do make protectors specifically for USB lines. (raychem among
others)

What would you suggest, include a polyfuse/fuse/active current limit?


The port is supposed to limit the current, a shorted peripheral, or one that
draws more than 100mA without getting permission, shouldn't take down the
hub.

2007\01\29@145412 by Wouter van Ooijen
face picon face
> USB power is not guaranteed to be current-limited.  On my computer, it
> is tied directly to the +5V rail.  If you draw more than about 30
> amperes, the computer will reset.

"guaranteed" is a difficult word. Let's take the lawbook to give the
'kast word' on this:

(quote) USB spec 2.0 : 7.2.1.2.1 Over-current Protection

The host and all self-powered hubs must implement over-current
protection for safety reasons, and the hub must
have a way to detect the over-current condition and report it to the USB
software. Should the aggregate current
drawn by a gang of downstream facing ports exceed a preset value, the
over-current protection circuit removes
or reduces power from all affected downstream facing ports. The
over-current condition is reported through the
hub to Host Controller, as described in Section 11.12.5. The preset
value cannot exceed 5.0 A and must be
sufficiently above the maximum allowable port current such that
transient currents (e.g., during power up or
dynamic attach or reconfiguration) do not trip the over-current
protector. If an over-current condition occurs on
any port, subsequent operation of the USB is not guaranteed, and once
the condition is removed, it may be
necessary to reinitialize the bus as would be done upon power-up. The
over-current limiting mechanism must be
resettable without user mechanical intervention. Polymeric PTCs and
solid-state switches are examples of
methods, which can be used for over-current limiting.

(/quote)

So connecting the USB power directly to a 10A+ PC PSU is not USB
compliant. But a slave that plans to short the power lines must be ready
to face 5A, and after that even the whole USB bus might have to be
reset.

I have my doubts about the last sentence: isn't a PTC quite slow, so it
would allow a much higher current for a short time, which would exceed
5.0A?

Wouter van Ooijen

-- -------------------------------------------
Van Ooijen Technische Informatica: http://www.voti.nl
consultancy, development, PICmicro products
docent Hogeschool van Utrecht: http://www.voti.nl/hvu


2007\01\29@202750 by peter green

flavicon
face

> No you can't. But at least you should try.
> USB power greater than 48V could be found only in software...
> :)
hmm, or a usb counterpart to the etherkiller ;)


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