CompuLab Face, Руководство по конструкции, Страница: 15 / 17

Electrical design recommendations
Revised February 2012 FACE Module Design Guide
15
5.4 USB Design Guidelines

No termination resistors are required.

Target impedance for USB differential pairs should be 90 Ω ± 15%.

Trace spacing should be ≥ 4:1 on both sides of the pair.

Avoid stubs or test points on the signal pairs.

Provide ESD suppression components for any USB pair that is accessible to the end user, and
optionally for any USB pair that is not accessible to the end user. No stubs are allowed from the
USB signals to the ESD components. Place these components between the common mode choke
and connector. It is recommended to place ESD suppression components as close as possible to
the connector and at no further than 0.5” from the connector body.

Decouple the ESD suppression component with a high frequency capacitor placed directly across
the device power and GND pins, no further than 50 mils away.

Provide the option for a common mode choke for EMI suppression for any USB pairs that can be
connected to cabled devices. The chokes should be bypassed with 0-Ω resistors by default. The
resistors must be located under the choke to minimize stubs. Place the choke within 1.0” of the
USB connector.

Please refer to the reference schematics and layout designs available in the FACE module design
package.
5.5 Power Supplies Design Guidelines

Implement FACE module power supply rails with DC-DC switching regulators.

12V power rail should be used to supply the FACE module DC-DC switching regulators.

Maximal current consumption from the 12V power rail should not exceed 1A.

Maximal current consumption from the 5V power rail should not exceed 2A.

SLP_S3# signal may be utilized to implement power supply control. Please note SLP_S3#
polarity requirements.

Please refer to the reference schematics and layout designs available in the FACE module design
package.