Nxp Semiconductors ISP1562 User Manual

 

 

AN10050_4 

© NXP B.V.  2007. All rights reserved.

•  The maximum allowed length of the DP and DM lines for onboard solutions (or [trace 

+ cable length] for a front-panel solution) is 18 inches. 

•  A decoupling capacitor must be placed on V

BUS

 as close as possible to each USB 

connector. A value of about 150 µF/10 V is recommended on each port. 

•  The common-mode choke used, if really necessary, on the DP and DM lines must be 

placed as close as possible to the USB connector and must have  
Z

com

 < 8 

Ω @ 100 MHz and Z

diff

 < 300 

Ω @ 100 MHz. 

•  The common-mode choke, as well as the ElectroStatic Discharge (ESD) protection 

components will be used only if necessary (in case the design does not pass EMI or 
the ESD tests) because these may affect the signaling quality. Nevertheless, it is 
recommended that you include the necessary footprints for common-mode chokes 
and ESD protection components on the PCB as safeguards. The footprints must be 
placed as close as possible to the USB connector. Special attention must be given 
when placing additional components on the DP and DM lines and routing 
recommendations must be followed. 

•  Both V

DDA_AUX

 (analog) and 

V

CC(I/O)_AUX

 (digital) are derived from the PCI V

AUX 

voltage, 

found on pin A14 of the PCI connector. 

V

CC(I/O)_AUX

 can directly be connected to PCI 

V

AUX

. V

DDA_AUX

 is separated from PCI V

AUX

 by an inductor and each of 

V

CC(I/O)_AUX

 and 

V

DDA_AUX

 uses its own decoupling capacitors. 

•  The design must ensure that the V

DDA_AUX

 and 

V

CC(I/O)_AUX

 power planes are isolated 

from the main PCI 3.3 V power plane. This is achieved by creating two separate 
power planes that do not come in contact with the PCI 3.3 V power plane. 

•  The decoupling capacitors must be placed as close as possible to the ISP1562/3. A 

good choice is the four corners of the IC because these areas will not normally be 
occupied by traces or other components, according to the ISP1562/3 pinout. 

•  For good EMI testing results, it is recommended that you provide a good path from 

the USB connector shell to the chassis ground. The USB connector shell must be 
connected to an isolated ground plane. 

For more information, refer to the Intel document The USB 2.0 Platform Design 
Guideline, Rev. 1.0.