Размышления о качестве USB кабеля

Introduction

This technical note will assist you in selecting the
correct USB cable for the MCA527. The USB
interface is used today nearly everywhere where
computers are in operation. USB cables are available
from a lot of wellknown but also from noname
manufacturers and assumed as standard products with well
defined and guaranteed parameters. This is
a great misjudgement! There are cables with different
parameters and not every cable can be used for all
applications. Some cables on the market don’t meet
the USB specification under no circumstances and
shouldn’t be used. Furthermore, the different USB
specifications define various connectors which are
not completely mechanical compatible to each other.
Choosing the wrong cable may result in an unstable
USB connection or an undefined device operation.
Sometimes the USB device isn’t detected correctly by
the USB host and cannot be operated. Choosing a
cable with wrong plugs always results in no
connection.

и выводы в заключении

Conclusion
Use only USB1.1 or USB2.0 cables with a
standard B plug on one side and a type A plug which
mates to your host computer on the other side to
operate the MCA527. The cable shouldn’t be longer
than 5 meters because longer cables are not
compliant with the USB specification. Avoid to use
extension cords, they are not compliant with the USB
specification. When used, the power conductor’s
overall DC resistance must not exceed the value
required by the application (0.25Ω). Furthermore, the
overall length must not exceed 5 meters. Make sure
that the conductor crosssection of the two power
conductors corresponds with the cable length. Take
care about the conductor material. For the MCA527
only copper cables are suitable. We recommend to
use a standard USB2.0 cable from TE Connectivity
(www.te.com), for example part number 14875963
(1.8m) or 14875982 (5m).
Do not use active cables (repeater cables).
Usually they are bus powered hubs and cannot
operate high power devices. Do not operate the
MCA527 on a buspowered hub. Actually, this should
not work but most buspowered hubs on the market
identify themselves as powered hubs. Under some
circumstances the input voltage on the MCA527 can
fall below 4.5V and may cause malfunction.
When only a bad USB cable is available, operate
the MCA527 with its battery charger. Then the current
on the USB power lines decreases to a few
milliamperes and therewith the voltage drop on the

power lines is negligible
[gview file=»http://www.gbs-elektronik.de/fileadmin/download/manuals/TN_Choosing_USB_Cable.pdf»]

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