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USB2229
Microchip USB2229 Handleiding
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SMSC AN 14.18 APPLICATION NOTE Revision 0.96 (06-01-06)
AN 14.18
Design Guidelines for
USB22XX/USB260X
High-Speed SD
1 Introduction
This application note provides information on Printed Circuit Board layout for High-Speed Secure-Digital
(SD) media sockets with USB22XX and USB260X.
2 Overview
Successful High-Speed operation of Secure-Digital media with USB22XX and USB260X requires
special consideration for Printed Circuit Board (PCB) layout. This application note describes the
important items to consider for layout of PCB.
3 PCB Layout Guidelines
The guidelines presented are applicable to all SMSC card-reader products that support High-Speed
Secure-Digital operation. Guidelines for both two-layer and four-layer PCBs are presented here.
3.1 Power and Ground Distribution to SD Socket
Ground connection between the card-reader and the media socket is important, both for supply return
current and signal return currents. The ground should be solid, have low impedance and few
constrictions between the card-reader and the socket. The card-reader supplies the power to the socket
in most applications since the power-FET is built-in to the SMSC card-reader.
SD socket VDD supply trace from card-reader should be 20 mils wide, 0.5 oz or thicker for a length
up to 3000 mils.
SD socket ground connection: plane, 0.5 oz or thicker, between socket and card-reader.
Note: No constrictions or cuts allowed in the ground between card-reader and socket.
3.2 Signal Traces to SD Socket
The Secure-Digital interface has a total of seven signals to the card-reader. Six of these signals are
critical for high-speed operation: SD_DAT[0:3], SD_CMD and SD_CLK and require special
considerations.
Signal traces must be above a solid and continuous ground plane along the path from card-reader
to socket.
SD_CLK trace requires two grounded guard-traces, one on each side spaced, at 3 times minimum
spacing.
SD_CLK guard traces must have a via connecting to the ground plane at both ends and every 500
mils along the path.
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Specificaties
| Merk: | Microchip |
| Categorie: | Niet gecategoriseerd |
| Model: | USB2229 |