Layout Notes - Intel PXA27 Series Design Manual

20.4

Layout Notes

The USB power supply must be +5.0 V (per the USB specification). However, the PXA27x
processor does not have 5.0 V tolerant inputs. System designers must provide an external device to
interface the USBHPENx and USBHPWRx pins to the power supply and over current detection
circuits.
The C and R
P
USBH_N<3:1> signal compliance with the USB specification and must be placed as close as
possible to the PXA27x processor USBH_P<3:1> and USBH_N<3:1> ball pads.
The R pull-down resistors shown on the USBH_P<3:1> and USBH_N<3:1> signals are required
P
per USB specification.
Terminations and filtering for signal integrity and electrostatic discharge (ESD) protection circuitry
are recommended, but varies for different systems depending upon layout and end application
environment.
USBH_P<3:1> and USBH_N<3:1> are differential pair signals. Use these recommended layout
guidelines:
•
Route the signals close to each other as parallel traces on the PCB.
•
Match the trace lengths as closely as possible (within ±0.5 inches (12.7 mm)).
®
Intel PXA27x Processor Family Design Guide
components are required by the USB Host controller for USBH_P<3:1> and
S
Universal Serial Bus Host Interface
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II:20-5