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PCB Design and Layout Guide

Single Port 10/100/1000BASE-T

Introduction

This purpose of this application note in conjunction with the VSC8201 Datasheet is to provide information to assist in the design and lay-

out of the VSC8201 Gigabit Ethernet Transceiver.

Power Supply Organization and Decoupling

The VSC8201 requires a 3.3v and a 1.5v power supply source for operation using GMII, MII or TBI MAC interfaces. In RGMII and RTBI

modes, an additional 2.5v supply is needed as specified by the RGMI/RTBI standard. The VSC8201 can be powered using the following

options:

•

2 separate supplies, 3.3v and 1.5v respectively.

•

A single 3.3v supply. This is done by using the optional on-chip regulator control circuit, which drives a simple external series pass

type supply regulator (MOSFET) to generate the 1.5v core power supply.

PCB Power Plane Organization

It is recommended that the PCB power plane(s) in a system be divided into four separate regions:

Power Supply Filtering and Decoupling

For best performance, each power supply region should contain capacitors for both bulk decoupling and for local high-frequency decou-

pling. This is summarized in the following tables:

Table 1: Power Supply Plane Regions

PCB Power

Plane

Description

Nominal

Supply Voltage

regulator power dissipation but including external twisted pair termination; all worst case current figures have all nominal power supplies

scaled by +5%.

b. Refer VSC8201 Datasheet to correlate supply names with part pin numbers.

Typ

Max

V+IO

Digital Input/Output

buffer supply

3.3v/2.5v

8mA

11mA

VDDIO

V+A33

Filtered analog 3.3v

supply

3.3v

101mA

111mA

TXVDD, VDDREC33,

VDDPLL33

V+A15

Filtered analog 1.5v

supply

1.5v

41mA

48mA

VDDREC15, VDDPLL15

V+DIG

Digital core supply

1.5v

350mA

423mA

VDDDIG