AN2674 datasheet(14/22 Pages) STMICROELECTRONICS

부품명	AN2674

상세설명	PCB layout guidelines for SPEAr3xx

PDF	22 Pages

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제조업체	STMICROELECTRONICS [STMicroelectronics]

홈페이지	http://www.st.com

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14 / 22 page

USB interface

AN2674

14/22

Doc ID 14204 Rev 2

3.2

USB decoupling and reference resistor

Decoupling capacitors should be placed as close as possible to the power balls, preferably

directly under the power balls using short wide connecting traces. Placing decoupling

capacitors at a distance degrades the performance, which can result in interoperability

problems and compliance violations with the specifications.

Figure 5.

Example of USB decoupling capacitor bottom mounted layout

Legend:

Blue: top layer of PCB

Orange: bottom layer of PCB

Cyan traces: USB data pairs.

Table 4.

USB power, ground, and reference guidelines

Guideline

*VSS*

Connect all VSS pins directly to the internal PCB ground plane

*VDD*

Connect all VDD pins to 100 nF capacitors under the ball using a short wide

trace

USB_RREF

External reference resistor (43.2 ohm). Connect resistor to ground.

AN2674 데이터시트(PDF) 14 Page - STMicroelectronics