EVALUATION AND DESIGN SUPPORT
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CIRCUIT FUNCTION AND BENEFITS
The universal serial bus (USB) is rapidly becoming the standard
interface for most PC peripherals. It is displacing RS-232 and
the parallel printer port because of superior speed flexibility
and support of device hot swap. There has been a strong desire
on the part of industrial and medical equipment manufacturers
to use the bus as well, but adoption has been slow because there
has not been a good way to provide the isolation required for
connections to machines that control dangerous voltages or low
leakage defibrillation proof connections in medical applications.
The
for a peripheral USB device. However, there are occasions when
it is useful to create an isolated cable function. Several issues
must be addressed to use the
Whereas the buffers on the upstream and downstream sides of
the
cable, the downstream buffers must be capable of adjusting
speed to a full or low speed peripheral that is connected to it.
The upstream connection must act like a peripheral, and the
downstream connection must behave like a host.
Unlike the case of building a dedicated peripheral
interface where the speed is known and not changed,
host applications must adapt to detect whether a low
or full speed device has been connected. The
is intended to be hardwired to a single speed via pins; therefore,
it works when the peripheral plugged into its downstream side
is the correct speed, but it fails when the wrong speed
peripheral is attached. The best way to address this is to
combine the
Rev. A
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Schematics, Layout Files, Bill of Materials
CN-0159 Circuit Evaluation Board
ADuM4160
ADuM4160
ADuM4160
are the same and capable of driving a USB
is designed primarily as an isolation element
Circuits from the Lab™ tested circuit designs address
common design challenges and are engineered for
quick and easy system integration. For more information
and/or support, visit
with a hub controller.
ADuM4160
Universal Serial Bus (USB) Cable Isolator Circuit
for this application.
www.analog.com/CN0159.
ADuM4160
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781.329.4700
Fax: 781.461.3113
The upstream side of a hub controller can be thought of
as a standard fixed speed peripheral port that can be easily
isolated with the ADuM4160, whereas the downstream ports
are all handled by the hub controller. However, in many cases,
while it is not certifiable as fully USB compliant, a single speed
cable is acceptable from a practical standpoint, especially if
custom connectors are used so that it cannot be confused with a
compliant device. The hub chip can be eliminated, and the
design becomes very small and simple.
The
implement an isolation buffer for medical and industrial
peripherals. The challenge that must be met is to use this to
create a bus-powered cable isolator by pairing the
with a small isolated dc-to-dc converter such as the
ADuM5000. As with isolating any device, the services that
the
The goal of the application circuit shown in Figure 1 is to isolate
a peripheral device that already implements a USB interface. It
is not possible to make a fully compliant bus-powered cable
because there are no 100% efficient power converters to transfer
the bus voltage across the barrier. In addition, the quiescent
current of the converter does not comply with the standby
current requirements of the USB standard. This is all in
addition to the speed detection limitations of the ADuM4160.
What can be achieved is a fixed speed or switch-controlled
speed cable that can supply a modest power to the downstream
peripheral. However, it is a custom application that is not
completely compliant with the USB standard.
ADuM4160
ADuM4160
1.
2.
3.
4.
5.
Directly isolates, in the upstream, the USB D+ and
D− lines of a cable.
Implements an automatic scheme for data flow of
control that does not require external control lines.
Provides medical grade isolation.
Supports full speed or low speed signaling rates.
Supports isolated power delivery through the cable.
Devices Connected/Referenced
ADuM4160
ADuM1100
ADuM5000
provides are as follows:
provides an inexpensive and easy way to
©2010 Analog Devices, Inc. All rights reserved.
Full/Low Speed USB Isolator
Digital Isolator
Isolated DC-to-DC Converter
Circuit Note
www.analog.com
CN-0159
ADuM4160