Cypress Semiconductor Corporation • 3901 North First Street • San Jose, CA 95134 • 408-943-2600
Revised January 31, 2005
Migrating From EZ-USB FX2™ to EZ-USB FX2LP™
Abstract
The FX2LP is a next-generation USB high-speed controller.
FX2LP enhances the functionality of the FX2 while
minimizing the effects on existing designs. The purpose of
this application note is to expedite the developer’s learning
curve regarding the migration of a CY7C68013 (EZ-USB
FX2) design to use the CY7C68013A (EZ-USB FX2LP)
microcontrollers. This application note highlights the
difference between the two products and aids the designer in
migrating existing designs to FX2LP. The application note
also provides a brief description of the collateral available for
development work with FX2LP.
Hardware Changes
Changes on Crystal Specification
With the use of FX2LP one change is required. When a
crystal is used in the design, for proper operation the load
capacitance of the crystal is required to change. This effects
both the load capacitors and the crystal being used. The
CY7C68013 requires a crystal with load capacitors that are
between 20 pF and 33 pF. The CY7C68013A requires a
crystal with load capacitors of 12 pF. If redesigning an FX2
application with FX2LP, the crystal is required to change to a
load capacitance of 12 pF, and the matching load capacitors
must change to 12 pF. This is a requirement of all designs
using FX2LP.
Following is the spec on the crystal
• 24 MHz +
100 ppm
• Parallel resonant
• Fundamental mode
• 500 µW drive level
• 12-pF (5% tolerance) load cap
One of the parts we recommend is one from Ecliptek:
EC-12-24.000M
The above specification must betaken into consideration
while selecting both the load capacitors and the crystal. Using
a different crystal load capacitance with a crystal specified for
12 pF is expected to have some effect on the frequency shift.
It is recommended that the designer always make sure that
the power dissipated by the crystal is with-in the crystal
manufacturer’s specifications. Over-driving the crystal may
damage the crystal. Refer to the specific crystal manufac-
turer’s recommendations.
An article on crystal design and selection from Ecliptek's site
(http://www.ecliptek.com/crystals/glossary.html) states the
following
“The rate of aging is typically greatest during the first 30 to 60
days after which time the aging rate decreases. The following
factors effect crystal aging: adsorption and desorption of
contamination on the surfaces of the quartz, stress relief of
the mounting and bonding structures, material outgassing,
and seal integrity.”
One of the effects of over-driving the crystal out of its specified
conditions may be aging of the crystal which is expected to
result in frequency shift. From speaking to various crystal
manufacturers, we have been informed that the majority of
the shift due to aging usually occurs in the first 45–60 days or
so.
In general, it is recommended that a designer always make
sure that the power dissipated by the crystal is within the
crystal manufacturer’s specifications. Over-driving the crystal
may have adverse effects on the crystal performance and
accuracy. It is also recommended that the user refer to the
crystal manufacturer’s recommendations on the various
effects of driving a crystal beyond its specified values.
The CY7C68013 requires a crystal with load capacitors that
are between 20 pF and 33 pF, while the CY7C68013A
requires a crystal with load capacitors of 12 pF. During the
development phase, for test purposes, an existing BOM that
has a crystal with 20 pF to 33 pF should be used to operate
a CY7C68013A at room temperature.
There has been reports from few FX2LP customers that the
use of the same crystal with 16-pF or 20-pF load capacitance
does not seem to cause any problems. Please be informed
that even though the crystal with load capacitance of 16 pF or
20 pF appears to work (and most probably will work for a long
time) we are unable to provide test reports or any test data on
this, as the part was designed and tested to use the crystal
as specified above.
Using a 16-pF or 20-pF crystal, or for that matter any other
standard load capacitance, may and most probably will work
as indicated by the discussions we have had with various
crystal manufacturers. But using this is at the customers
discretion as the FX2LP part was only tested and designed
for a 12-pF, 24-MHz crystal. Please consult with the specific
crystal manufacturer for information on the various effects of
driving a crystal beyond its specified values. When a crystal
is used in the design using FX2LP, Cypress recommends that
for proper operation the load capacitance of the crystal should
be 12 pF.
Changes on AVCC/AGND Pin Functionality
As far as PCB changes are concerned, there are no major
ones. Both FX2 and FX2LP run on a single 3.3V supply.
There are two additional AVCC/AGND pins on the FX2LP that
can be re-routed on the PCB to provide additional filtering.
These two additional pins exist in the 56-, 100-, and 128-pin
packages.
For the 128-pin TQFP package, AVCC is pin 17 (was VCC on
the FX2), and AGND is pin 20 (was GND on the FX2). Pin 17
of the FX2LP128 pin package does not need a duplicate of
the pin 10 AVCC filter network. It can be wired in parallel to
pin 10.
(36 paginas)
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