AND8130 Datasheet, PDF (1/4 Pages) ON Semiconductor – Analog Switch Allows USB Switching at Low Voltages

AND8130/D
Analog Switch Allows USB
Switching at Low Voltages
Prepared by: Fred Zlotnick
ON Semiconductor
http://onsemi.com
APPLICATION NOTE
EXECUTIVE SUMMARY
The new NLAS2066 is a dual SPST (Single Pole Single
Throw) switch with over−voltage tolerance (OVT) in it’s
input pins. The OVT feature permits the device to be used
for the purpose of sharing of pins in size constrained
applications. Shared pins permit the designer to have a
smaller connector, saving cost on both male and female
portions.
INTRODUCTION
Our modern world is filled with many new devices that
permit the user to communicate, take photos and short
videos, and listen to music and a whole host of features not
yet on the market. The USB port of a modern computer is the
most convenient, easiest to use, high performance
connection point the consumer can deal with. Although
there are other useful ports, the USB port offers simple
hookup, up to 2.5 watts of power, and speeds from 100
Kbits/sec to 400 Mbits/sec.
A USB port has 4 wires, 2 for bidirectional data, and two
for power. A USB port can supply as much as 500 mA at 5.0
V. Many devices simply plug into the USB port with no need
for an external power supply. Most users are already familiar
with USB peripherals such as printers, pointing devices,
keyboard, and digital still camera. Most peripherals just
“plug and play”. Modern P.C.s take care of the interface with
minimal effort, only requiring the installation of software
drivers. In addition, the number of USB ports can be
increased by adding a hub. USB simply works very well and
is the simplest, most convenient port a consumer can deal
with.
USB 1.1/2.0
USB 2.0 adds a High Speed specification to the original
USB v. 1.1 specification. There are three speeds for USB v.
2.0. The three speed ranges are:
Low Speed: 10−100 Kbits/sec
Full Speed
500K−10 Mbits/sec
High Speed 25−400 Mbits/sec
All USB devices are backward and forward compatible
with both the older 1.1 and 2.0 revisions. If the user had a
device that he recently purchased that is rated as High Speed,
he can still use it with an older PC that only supports the Full
Speed mode.
With its ease of use, and inclusion on nearly all Windows,
Mac and Linux systems built since 1998, it is the ideal
interface for an enhanced feature cell phone. A phone with
a 64 MB card can be updated in a few minutes, even in the
Full Speed mode. Photos, music, address books can all be
updated in just a few seconds. When attempting to add USB
to a device like a cell phone the designer has several issues.
Adding an additional connector adds cost and takes up
space. Adding 4 more pins to the existing connector adds
cost to both the female portion in the phone and all the
various male connectors that need to be supplied, in the form
of “dongles”. One way to simplify the whole system is to
multiplex some of the pins.
MULTIPLEXING PINS
This article will only concern itself with the multiplexing
of the data pins. The power pins provide capability to
re−charge the phone, without need for a wall mounted power
supply. With the close proximity of the wires and the
possibility of a potential fault from the power line to the data
line, specification assumes the data lines can handle a
voltage up to 5.25 V at the data line¹ for up to 24 hours. The
data is sent differentially as NRZI at a maximum of 10
MBits/sec. The cell phone manufacturer must supply
interface cables. The standard USB Type B, at
approximately 11 x 11 mm, connector probably is too large
for a cell phone. Normally a dongle² is provided with a
non−standard plug on the one side and a standard USB type
“A” plug on the other. Depending upon the features of the
cell phone, the socket may provide audio, video, RS−232, or
other interfaces.
1. Universal Serial Bus Specification, Revision 2.0 April 26,
2000.
2. A flexible cable with appropriate connectors on both ends.
© Semiconductor Components Industries, LLC, 2003
1
August, 2003 − Rev. 0
Publication Order Number:
AND8130/D