PCB Design Recommendations Specification Sheet

ManualsBrandsCypress ManualsNetwork CardEZ-USB FX2 PCB

November 21, 2002 Document No. 001-43117 Rev. ** 1

EZ-USB FX2™ PCB

Design Recommendations

Introduction

This application note presents recommendations for design-

ing with the Cypress Semiconductor EZ-USB FX2™ compo-

nent. Techniques for high-speed design should be applied to

circuits using the EZ-USB FX2. Due to the packaging and

high performance characteristics of the EZ-USB FX2, consid-

eration of the PCB thermal design is required.

CY4611 EZ-USB FX2 USB to ATA Reference

Design

A complete design using the Cypress CY7C68013 EZ-USB

FX2 is available. The design implements the recommenda-

tions of this application note. It may be useful for the reader to

download the CY4611 Reference Design Files from the

Cypress Support page for Reference Designs.

Figure 1. FX2 (CY4611) USB to ATA Reference Design

Cypress offers the CY4611 EZ-USB FX2 USB to ATA Refer-

ence Design as an evaluation platform for developers wishing

to integrate a USB 2.0 Peripheral Controller into their applica-

tion. The kit includes the EZ-USB FX2 USB to ATA evaluation

board, USB cable, schematics, bill of material, PCB Gerber

files, and other documentation.

EZ-USB FX2 Package Description

The CY7C68013-56LFC EZ-USB FX2 component is pack-

aged as a 56-pad, 8-mm by 8-mm, 1-mm high, QFN (Quad

Flatpack No leads) package. Please refer to the latest

CY7C68013 EZ-USB FX2 USB Microcontroller High-speed

USB Peripheral Controller data sheet for the detailed pack-

age drawing. The data sheet is Cypress specification 38-

08012.

This package is comparable to the Amkor MicroLeadFrame™

package. It is a plastic encapsulated, near-chip scale pack-

age using solder lands instead of leads or balls. It uses a cop-

per leadframe substrate that provides for short die to frame

lead length giving good high-frequency performance. It has

an exposed die paddle that enables good thermal transfer out

of the package. For further details about this package and

methods and processes associated with its assembly to a

printed circuit board, please refer to the manufacturer's appli-

cation note identified in the References section of this docu-

ment.

Electrical Design Recommendations

USB 2.0 high-speed signaling is used to transfer data at 480

Mbps. This rate is 40 times higher than the highest speed of

the USB 1.1 specification, full-speed signaling that operates

at a 12-Mbps rate. High-speed signaling requires a greater

level of attention to electrical design than previously required

for USB designs. Careful attention to component selection,

supply decoupling, signal line impedance, and noise are

required when designing for high-speed USB. These physical

issues are mostly effected by the PCB design and is pre-

sented in the PCB Design Recommendation section.

One key measurement of USB data signal quality is the eye

pattern. The eye pattern is a representation of USB signaling

that provides minimum and maximum voltage levels as well

as signal jitter. Section 7.1 in the USB 2.0 Specification pro-

vides detailed explanation and requirements for a compliant

eye pattern. Figure 2 is an eye diagram of high-speed signal-

ing as measured on the EZ-USB FX2 component.

AN1196

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Summary of content (7 pages)

PAGE 1
EZ-USB FX2™ PCB Design Recommendations AN1196 Introduction EZ-USB FX2 Package Description This application note presents recommendations for designing with the Cypress Semiconductor EZ-USB FX2™ component. Techniques for high-speed design should be applied to circuits using the EZ-USB FX2. Due to the packaging and high performance characteristics of the EZ-USB FX2, consideration of the PCB thermal design is required.
PAGE 2
AN1196 Figure 2. FX2 Eye Diagram of High-speed Signaling The specific recommendation for the ceramic capacitor nearest each EZ-USB FX2 power pin is given in Table 1 below. Table 1. Capacitor Recommendation QFN Pin Number Capacitor Value QFN Pin Number Capacitor Value 0.1 µF 7 0.01 µF 43 11 0.001 µF 55 0.1 µF 17 0.1 µF 3 0.1 µF 27 0.1 µF 3 2.2 µF 32 0.
PAGE 3
AN1196 Maintain PCB Trace Impedance Designing the PCB traces for particular characteristic impedance is very important to signal quality. The USB specification requires controlled impedance among all elements in the USB data path. The differential impedance of each USB data pair should be 90 ohms with a 10% tolerance to match the differential output impedance of high-speed capable drivers. A common way to implement a differential pair is to use an edge-coupled, surface micro-strip line.
PAGE 4
AN1196 This figure shows the dielectric material thickness (“Prepreg”) between layers 1 and 2 and the thickness between layers 3 and 4. The dimensions between these layers are a key element in the design to set the proper characteristic impedance for the USB data traces. This is the “h” term mentioned in the prior section on PCB impedance design. The core material of the PCB lies between layer 2 and 3.
PAGE 5
AN1196 The design of the land area for the exposed paddle is critical to proper thermal transfer. A copper fill is to be designed into the PCB and under the QFN in order to assist thermal transfer. Figure 5 is the diagram of the PCB land area for the EZUSB FX2. Figure 7 shows the solder mask region at the package. Each of the 25 plated through-holes is in the center of each circle of solder mask. Black area indicates absence of solder mask. Figure 7. Solder Mask Figure 5.
PAGE 6
AN1196 EZ-USB FX2 Assembly Recommendations The solder stencil over the exposed paddle is required to permit at least 50% solder application coverage. Figure 8 is a graph from Amkor research showing how solder void much less than 50% has little influence on thermal transfer. The package is a smaller one than the EZ-USB FX2 8-mm 56lead package, but the values do scale. Figure 8. Thermal Performance versus Solder Void Figure 9 shows that the stencil area contains 25 holes.
PAGE 7
AN1196 References Cypress, CY4611 FX2 USB to ATA/CF Reference Design Kit, Cypress Semiconductor, California, 2002. Cypress, Cypress Semiconductor web site, www.cypress.com/, Cypress Semiconductor, California. USB-IF, Universal Serial Bus Specification, Revision 2.0, USB Implementers Forum, Oregon, 2000. USB-IF, USB Developers web site, www.usb.org/developers/, USB Implementers Forum, Oregon.