AN-5015 Datasheet, PDF (1/6 Pages) Fairchild Semiconductor – Transceiver and Specification Compliance

AN-5015
Fairchild Semiconductor
Application Note
December 1999
Revised December 2000
USB1T11A Transceiver and Specification Compliance
Introduction
The Universal Serial Bus (USB) specification has become
widely accepted as the preferred mechanism for low to
medium speed serial data interfaces. Older connections
like RS232 and parallel printer LPTx ports can only be con-
nected to one device at a time. USB allows multiple
devices to be attached to a single port enabling greater
system flexibility. The USB specification also allows for the
connection, immediate operation, and removal of these
devices with the system running. With widespread use
comes the need to develop low cost, specification compati-
ble, interface devices. An USB implementation example is
shown in Figure 1.
related to driving and receiving differential signals on
the USB cable.
2. Isolates the digital controller from the cable. Guaran-
teed ESD tolerance on the transceiver ensures the
expensive controller will not be damaged by adverse
signals on the cable.
3. Removes analog style signals from the digital control-
ler. This allows the design of the digital controller to be
optimized for USB logic functionality. Keeping the con-
troller completely digital reduces the design “risk” and
added cost of a mixed analog and digital design.
Transceiver Block Diagram and Pinout
FIGURE 1. USB with Integrated Transceiver
Benefits of
Standalone Transceiver
Removing the transceiver function from the Digital Control-
ler and Serial Interface Engine (SIE) has three main bene-
fits.
FIGURE 2. USB with Standalone Transceiver
1. Removes signal integrity concerns from the digital con-
troller. The standalone USB Transceiver is responsible
for meeting all compliance and signal quality issues
FIGURE 3. Functional Diagram and Pinout
Transceiver Features
1. Converts USB differential voltages to digital logic signal
levels.
2. Converts the D+ and the D− line to single ended logic
outputs for SE0 (single-ended 0) detection.
3. Converts logic levels to different USB signals.
• Runs at low or high speed
• Selectable output slope control
• Meets the USB 1.1 drive template
• Has low power standby mode
4. Small footprint at low cost.
© 2000 Fairchild Semiconductor Corporation AN500357
www.fairchildsemi.com