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PDF CM2722 Data sheet ( Hoja de datos )
| Número de pieza | CM2722 | |
| Descripción | EMI Suppression | |
| Fabricantes | Steward | |
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Hay una vista previa y un enlace de descarga de CM2722 (archivo pdf) en la parte inferior de esta página. Total 4 Páginas | ||
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EMI Suppression for Firewire &
Overview
USB 2.0 Applications
A primary problem for the Firewire IEEE1394 and USB2.0 as with the USB1.1 port designer is
common mode noise conducted through the power and signal lines from various sources. EMI
susceptibility on data/power lines is also a major concern. The use of a common mode choke in
this application will provide a complete low cost, effective, modular, filter solution.
Steward’s CM2722 (for single and dual ports), CM3822 (for tri ports), and CM5022 (for quad
ports) series of components have the lowest normal mode impedance in the industry and
suppress a wide range of digital common mode noise. Normal mode impedance is net circuit
impedance i.e. the impedance seen by the differential signal.
Discussion
Firewire and USB2.0 is a serial data / power port providing a broad range of data and current loads. The initial USB industry
specification called for a serial port which operates in a hybrid full duplex mode and a power port that operates up to 1 amp of
current. This design has created several layers of EMI problems that must be corrected. Also, USB component performance
requirements have been stretched beyond initial specifications which has caused field failures of 1 amp and even 3 amp rated
ferrite chip beads. Firewire and USB2.0 have increased the expected design loading to a minimum of 4.0 amps to insure failure
free operation.
The source of most USB EMI problems is the two outside conductors in the connector for the power port. The primary problem is
conducted common mode noise on the power line and the best EMI solution is a common mode choke.
Common mode chokes have not traditionally been considered complete power and data line solutions because:
1. PROBLEM:
Traditional common mode choke geometry generates excessive normal mode impedance which causes failure in the
transmission signal integrity due to excessive net differential impedance in line. This is exacerbated with Firewire and
USB2.0 both of which are clocking at greater than 480 Mb/s, compared to USB1.1 which was operating @ 12Mb/s max.
STEWARD SOLUTION:
Steward’s unique product geometry minimizes net circuit Impedance at 500 MHz. The low normal mode impedance will
allow for video signals to pass through Steward’s common mode chokes without any perturbation to the picture quality.
Steward’s high performance common mode chokes have the lowest normal mode impedance in the industry today.
2. PROBLEM:
Traditional common mode chokes exhibit excessive amounts of crosstalk between data lines.
STEWARD SOLUTION:
Steward’s unique ferrite material used in all Steward multi-line common mode chokes has high volume resistivity (ohms
per cm) which eliminates electrical crosstalk. Also, Steward’s unique part geometry minimizes inter-winding capacitance
which is the primary source of crosstalk in most traditional wire wound common mode chokes. This is reflected in the
higher normal mode performance seen in other products.
3. PROBLEM:
The USB protocol is normally a fully differential serial data set in that D+ and D- are usually 180º out of
phase with each other. However, in low-Speed 1.5Mb/s and full-Speed 12Mb/s signaling as specified in
USB 1.1 there is a time period at the end of every packet of data called EOP. During this time period both
D+ and D- are held at approx. 0.8V for a specified period of time and this EOP signals an end of packet.
This state where both D+ and D- are held at the same potential is commonly known as the signal going
“single ended”. The “single ended” state can also be used as a reset to a downstream port and can wake
a USB device from the suspend state. The time period where D+ and D- are both at the same potential is
effectively a common mode signal and could be rejected by a high impedance common mode choke.
Steward North America - U.S.A. • Phone: +1 423 308 1690 • Fax +1 423 308 1622 • e-mail: [email protected]
North America - Mexico • Phone: +52 662 260-4832 • Fax: +52 662 216 1202 • e-mail: [email protected]
Europe - Scotland, UK • Phone: +44 (0)1506 414200 • Fax +44 (0)1506 410694 • e-mail: [email protected]
www.steward.com Asia / Pacific - Singapore • Phone: +65 6272 2646 • Fax : +65 6272 6165 • e-mail: [email protected]
China • Phone: +86-757-2563 8860 • Fax : +86-757-2563 8862 • e-mail: [email protected]
AN0007
REV 3 08/2004
1 page | ||
| Páginas | Total 4 Páginas | |
| PDF Descargar | [ Datasheet CM2722.PDF ] | |
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