EVALUATION AND DESIGN SUPPORT
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Design and Integration Files
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 this 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
implement isolation buffer for medical and industrial
peripherals. The challenges that need to be met are
1.
2.
3.
4.
5.
6.
The circuit shown in Figure 1 isolates a peripheral device that
already supports a USB interface. Because the peripheral is
not explicitly defined in this circuit, power to run the
secondary side of the isolator has been provided as part of the
solution. If the circuit is built onto the PCB of a peripheral
Rev. A
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suitability and applicability for your use and application. Accordingly, in no event shall Analog Devices
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whatsoever connected to the use of any Circuits from the Lab circuits. (Continued on last page)
CN-0160 Circuit Evaluation Board
Schematics, Layout Files, Bill of Materials
ADuM4160
Isolate directly in the USB D+ and D− lines allowing the
use of existing USB infrastructure in microprocessors.
Implement an automatic scheme for data flow of control
that does not require external control lines.
Provide medical grade isolation.
Allow a complete peripheral to meet the USB-IF certifi-
cation standards.
Support full speed (12 Mbps) and low speed (1.5 Mbps)
signaling rates.
Support flexible power configurations.
provides an inexpensive and easy to
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 http://www.analog.com/CN0160.
Universal Serial Bus (USB) Peripheral Isolator Circuit
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781.329.4700
Fax: 781.461.3113
design, power could be sourced from the peripheral’s off line
supply, a battery, or the USB cable bus power, depending on
the needs of the application.
The application circuit shown is typical of many medical and
industrial applications.
CIRCUIT DESCRIPTION
Power for the upstream USB connector is derived from the 5 V
VBUS voltage available on the USB cable. The peripheral device
must provide all of the signals and pull-up or pull-down
resistors that would be required if the ADuM4160 were not
present. The downstream side power is provided by a wall wart
and an
provides very low dropout voltage, thereby reducing the
regulation requirements on the wall wart. Its small size
(SOT-223) and 1 A current capability are ideal for this general-
purpose circuit where the peripheral device mau require cable
power to operate.
The ADuM4160 has several options for power, speed, and
protection that must be determined. The first is the speed at
which the peripheral runs. Peripheral devices run at one of
three speeds: low (1.5 Mbps), full (12 Mbps), and high speed
(480 Mbps). The ADuM4160 does not support high speed
operation and blocks handshaking signals that are used to
negotiate that speed. High speed mode starts as a full speed
configuration, and the peripheral requests high speed support
through a process called a high speed chirp. The ADuM4160
ignores the high speed chirp; therefore, the request for high
speed operation is never passed on to the host, and the
peripheral continues to work at full speed.The speed of the
peripheral on the USB bus is either low speed or full speed. The
particular peripheral determines the speed required, and the
ADuM4160 must be set to match this speed via the state of the
SPU and SPD pins. In the current schematic, the SPU and SPD
pins are tied to the internally regulated 3.3 V power supplies,
VDD1 and VDD2, setting the part for full speed operation.
ADP3338
Devices Connected/Referenced
ADuM4160
ADP3338
LDO regulator (5 V option). This LDO
©2010 Analog Devices, Inc. All rights reserved.
Full/Low Speed USB Digital Isolator
High Accuracy, 1 A, Low Dropout
Regulator (5 V Output Option)
Circuit Note
www.analog.com
CN-0160